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A Study of the - ----
Vegetation of Southeastern Washington
and Adjacent Idaho
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A THESIS PRESENTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR
OF PHILOSOPHY
BY
JOHN ERNEST WEAVER
SUBMITTED TO THE GRADUATE FACULTY OF THE UNIVERSITY
OF MINNESOTA. -
LINCOLN, NEBRASKA.
JANUARY, I917.
4.
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A STUDY OF THE VEGETATION OF SOUTHEASTERN
i:§
s WASHINGTON AND ADJACENT IDAHO
Q)
BY J. E. WEAVER
TABLE OF CONTENTS
PAGE
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Extent and position of area ....................................... 4
Physiographic regions and geology ................................ 4
Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Topography and drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
General plant-life conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I2
General vegetational distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I5
Outline of developmental series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I9
Evaporation and soil moisture in relation to succession . . . . . . . . . . . . . 2I
Soil temperature in relation to succession . . . . . . . . . . . . . . . . . . . . . . . . . . 37
The prairie-plains formation ...................................... 40
Agropyron-Festuca association . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Festuca consociation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Agropyron consociation ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Rhizocarpon-Lecidea associes . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Gyrophora-Parmelia associes . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Grimmia-Tortula associes .............................. 65
Poa-Polygonum associes . . . . . . . . . . . . . . . . . • • - - - - - - - - - - - 66
The desert scrub formation ........................................ 71
Artemisia-Atriplex association . . . . . . . . . . . . . . . . * * * * * * * * * * * * * * * * * * 72
Artemisia consociation . . . . . . . . . . . . . . . . . . . e s s is e e a e s e a e . . . . . 72
The Pacific Coast forest formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Thuja-Tsuga association ....................................... 74
Symphoricarpos-Opulaster associes . . . . . . . . . . . . . . . . . . . . . 75
Pinus-Pseudotsuga associes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Laria-Abies associes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Thuja consociation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Reprinted from UNIVERSITY STUDIES, Vol. XVII., No. 1, January, 1917.
33.37.4 ±
2 - A Study of the Vegetation of
Adsere. Alnus-Salix associes .......................... 90
Subsere. Natural reforestation in cut-over areas and in burns . . . . . . . 9I
Hydrosere . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . IOO
Chara-Potamogeton associes . . . . . . . . . . . . . . . . . . . . . . . . . . . IOI
Nymphaea-Potamogeton associes . . . . . . . . . . . . . . . . . . . . . . . IO2
Scirpus-Typha associes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IO3
Eleocharis-Carear associes . . . . . . . . . .‘. . . . . . . . . . . . . . . . . . . IO4
Wet meadow associes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IO5
Flood-plain forest associes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IO7
Ruderal vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I09
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III
INTRODUCTION
No one at all botanically inclined can travel through south-
eastern Washington without being impressed with the marked
changes which a distance of only a few miles may show in the
vegetation. Traveling eastward from a point fifty miles west of
the Idaho state line, one passes from a region of scab-land sage-
brush through one of rolling hills covered with bunch-grasses.
Upon steadily ascending the great Columbia Plateau, the bunch-
grasses give way to well developed prairies, and these in turn,
near the Idaho line, to forests of yellow pine, Douglas fir, white
fir, tamarack, and cedar. Or starting from Spokane in the central
part of eastern Washington and traveling southward, one soon
leaves the pine woodland of the Spokane gravels and passes again
through the rolling prairies. Projecting above the surrounding
sea of prairie-covered basalt are islands of quartzite, the tops of
lofty mountains almost buried under the basalt. These may be
covered with grass land on the windward side, while at a distance
of a few meters over the crest the prairie may give way to rather
dense forests. Cut through the layers of basalt, in a mighty
canyon, 1,600 feet deep, the Snake River winds its way through
the prairie belt. Upon descending into the canyon one finds the
bunch-grasses and sagebrush vegetation growing in a climate
markedly different from that of the plateau above. Far south-
ward from the canyon of the Snake River rise the pine-covered
foothills of the Blue Mountains.
Such is a brief glance at the wonderful field for investigation
2
Southeastern Washington and Adjacent Idaho. 3
offered the ecologist in southeastern Washington. It is a field in
which many stages in succession are offered within relatively easy
reach of a base station and one in which the vegetation so clearly
reveals adjustment to climatic and edaphic conditions that one
could scarcely wish for a better place in which to measure the
factors of the habitat and the vegetational responses. Moreover,
in this great inland province, practically no botanical work except
of a taxonomic character has been done (3, 9, Io, II).
Because of the high fertility of the deep basaltic soils, the
prairie region has largely been broken up for the growing of
wheat. Indeed, only isolated tracts of the best developed prairies
remain intact, while hundreds of acres of the drier bunch-grass
lands have been broken up during the time of the progress of
this work. It seemed unfortunate that a record of the rapidly
disappearing vegetation of this interesting region had not been
made. Accordingly, early in the spring of 1912, reconnaissance
work was begun, with Pullman, Washington, as the base station.
Ecological work was pursued vigorously in season and out
(with the exception of the summer of 1912) until the fall of 1914.
In the course of this investigation I have become indebted to
several persons to whom I wish to express my appreciation for
their services. I am pleased to express my appreciation first of
all to Dr. F. E. Clements, of the University of Minnesota, who
visited my field briefly in 1914, for many valuable criticisms and
suggestions. Dr. Raymond J. Pool, of the University of Ne-
braska, has read the first draft of this paper and I am grateful
to him for kindly suggestions. Thanks are due to Dr. T. C.
Frye, of the University of Washington, for the identification of a
number of mosses, and to the late Dr. H. E. Hasse of Santa Mon-
ica, California, who was kind enough to identify all of my lichens.
Wilting coefficient determinations of soils were made under the
direction of Dr. L. J. Briggs, of the United States Department
of Agriculture, to whom I wish to express my appreciation. The
chemical and physical analyses of soils were made by the depart-
ments of chemistry and soils respectively, of the Washington,
Agricultural Experiment Station at Pullman. I wish further to:
acknowledge my indebtedness to Mr. Walter L. Muenscher and
3
4. A Study of the Vegetation of
Mr. Earle Gibb, my one-time students, the former having assisted
me in the field during the entire summer of 1913, and the latter
during 1914. Finally, I wish to express my appreciation to Dr.
Harry B. Humphrey, now of the Bureau of Plant Industry, and
formerly my colleague in the Washington State College, for his
kindly interest in the work during the first year of the investiga-
tion. -
EXTENT AND POSITION OF THE AREA
The area under consideration includes approximately 4,OOO
square miles of territory located in southeastern Washington and
adjacent Idaho. On the south it extends toward the foothills
of the Blue Mountains, and reaches northward to the vicinity of
Spokane. Its western limit is about 50 miles from the Idaho
boundary, while in Idaho it includes a strip about 15 miles in
breadth. This area lies in the eastern part of the great Colum-
bia Plateau and extends eastward into the foothills of the Bitter-
root Mountains. The 47th parallel of latitude passes through
the center of this region, while it is bounded approximately on the
east and west by longitude II.7° and II.8° respectively. Alti-
tudinally, it ascends from about 1,175 feet on its western border
to a height of 4,000 feet in the mountains. The lowest point,
about 520 feet, is reached in the Snake River Valley, while Cedar
Mountain, near the Washington-Idaho line, reaches a height of
4,950 feet. While the above boundaries limit in a general way
the investigations recorded in this paper, without doubt the vege-
tation in adjoining regions is not far different from that here
described. - -
The peculiar topography, together with the range in altitude,
gives this area three clearly defined plant formations, ranging
from the desert-scrub formation, through the prairie formation
to the Pacific Coast forest formation. A brief statement of the
geology and topography of the region will help to make clear the
reasons for the present distribution of plant communities.
PHYSIOGRAPHIC REGIONS AND GEOLOGY
The part of the state of Washington lying east of the Cascade
Mountains is divided naturally into three great physiographic
4.
Southeastern Washington and Adjacent Idaho. 5
provinces. The Okanogan Highlands occupy the northeastern
part of the state, while the Blue Mountains cover a relatively
small area in the southeastern part. The remainder and larger
part of the area makes up the Columbia Plateau.
The Okanogan Highlands consist mainly of gently rounded
hills rising into peaks 4,900 to 6,600 feet high. Geologically, they
are similar to the northern part of the Cascades and are com-
posed largely of granite. They form, with the adjacent moun-
tains of British Columbia, a connecting link between the Cascades
and the Rocky Mountain system in Idaho. They are important
in connection with these studies mainly for the ameliorating effect
they exert upon the climate, and for the rôle they have played in
plant distribution in the foothills of the Bitterroot Mountains.
The portion of the Blue Mountains occurring in Washington
are composed wholly of basalt, and represent a great uplift of
this rock surrounding a central mass of granite peaks. In Wash-
ington they reach an elevation of more than 6,500 feet, while
in Oregon they rise about 3,300 feet higher.
The Columbia Plateau is thus bounded in Washington on three
sides by high mountain ranges, while in Idaho, on the east, it
merges into the Bitterroot Mountains. The plateau forms the
greater portion of eastern Washington, and is made up of an
immense mass of basalt, known geologically as the Columbia River
basalt. This basalt is the result of a series of lava overflows
which involved not only Washington, but also large areas in
Oregon and Idaho, and even northern California. In Washing-
ton it covered all of the region south of the Okanogan Highlands
and extended westward from the Bitterroot Mountains to the
Cascades. These basaltic lavas were extruded in a highly fluid
condition from numerous vents thickly strewn over the floor of
the region, and were spread over the surface in great flows (I,
I2, I3, I4). The apparently flat basaltic plains stand out in
sharp contrast to the mountain borders. The floor upon which
the lava was extruded had considerable relief and was not greatly
unlike the present Okanogan Highlands, with canyons, gorges,
and mountain peaks; the whole showing a state of vigorous dis-
section (14). The effect of the basaltic inundations was to fill
5
6 A Study of the Vegetation of
the valleys, and, to a large extent, bury the old topography. An
average thickness of at least 4,200 feet has been estimated for
the Columbia basalt in Washington. For the most part, the Co-
lumbia River lava completely covered all of the older rocks over
which it flowed. Exceptions to this appear in peaks which were
too high to be overwhelmed, such as Kamiak Mountain and Step-
toe Butte in eastern Washington. Likewise, old divides extend
into the basaltic fields as capes or promontories against which the
lava came to rest. These older rocks, like those of the foothills
of the Bitterroot Mountains, are mainly granites, gneisses, schists,
and quartzites. Canyon walls, notably those of Snake River, not
only reveal the older rock, but also expose the successive lava
flows with their beds of dust and lake deposits. Snake River
has cut down to a distance of over I,600 feet and has uncovered
in places the tops of buried mountains. Its canyon shows at
least ten overflows of the lava. Between some of these over-
flows sufficient time elapsed for soil to form and forests to grow.
The evidences of the latter appear either as charcoal or as silici-
fied tree trunks. Geological investigations indicate that the great
outpourings of lava were antecedent to the main uplift of the
Cascade Mountains. The appearance of these mountains so ef-
fectually modified the climate by cutting off the cool, moist, south-
west winds as to make much of the region eastward quite too
arid for forest growth. -
SOILS
The basalt, although hard and resistant to forces which abrade
it, yields with comparative rapidity to agencies which tend to dis-
integration and decay. The weathered basalt has decomposed
to form a rich residual soil which mantles the surface and gives
its slopes characteristically soft, rounded, flowing outlines. It
consists of a friable, dark-brown silt loam, with a depth ranging
from a few inches to several feet. The subsoil consists of a light-
brown silt loam. It is heavier and more compact and plastic
than the surface soil. Both soil and subsoil are extremely re-
tentive of moisture. They form a mantle usually many feet
deep, and only along the canyons of streams, or in the scab-rock
6
Southeastern Washington and Adjacent Idaho. *. 7.
in the western part of the area, is the basalt exposed. Westward
the soil becomes lighter in color, and in some cases is impregnated
with alkali.
Calkins (I) has advanced the theory that the soils in many
parts of eastern Washington have been formed by wind action
and are not of a residual nature. . His conclusion is based upon
the facts that in many parts of southeastern Washington there is
an absence of lamination in the soil, that it is extremely fine in
texture, that there is a remarkably sharp definition between the
soil and basalt, and that comparative chemical analyses indicate
soils not of the character naturally to be expected from the de-
composition of basalt in this climatic province. He believes the
principal source of the material was from the soft sedimentary
beds in the southwestern portion of the Columbia Plateau. How-
ever, the fact that there are no enclosed and undrained basins, as
there must be had wind been the only agent at work, leads one
to conclude that water erosion has also been an important factor
in forming the present topography.
By the action of water, and especially the prevailing southwest
wind, the plateau has been moulded into rounded hills not unlike
sand dunes. The soils are constantly shifting from south and
Southwest to north and northeast slopes. This gives better
weathering conditions on the exposed hillsides, while the soils
are deepest on the brows of the slopes where there is the most
favorable opportunity for the accumulation of wind-blown ma-
terial.
As is characteristic of dry regions, the transition from soil to
subsoil is not well marked, although the lighter-colored subsoil
appears nearer the surface on exposed than on sheltered slopes.
The proportion of clay is greatest towards the tops of the hills.
Humus increases as one goes down the slopes and is highest in
the valleys, where it forms a rich, black loam.
In contrast to the silt loam, grit-free soils covering the basalt, are
the sandy loam soils formed from the disintegration of quartzite,
granite, gneisses, and schists of the buttes and mountains. These
vary so widely in mechanical composition, water holding capacity,
7
8 A Study of the Vegetation of
and wilting coefficient, that they are considered in connection
with the plant communities which they support.
TOPOGRAPHY AND DRAINAGE
Viewed from the top of a bordering mountain, or, better, from
the summit of an isolated butte, the surrounding plateau looks

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FIG. I. Map of southeastern Washington and adjacent Idaho. The shaded
areas indicate coniferous woodland. Most of the outlying timbered areas are
characterized by yellow pine. West of the dotted line and in the canyon
of Snake River much of the area is characterized by scab-land covered
with sagebrush or bunch-grass. -
8
Southeastern Washington and Adjacent Idaho. 9
not unlike the billowy surface of the ocean. The fine silt loam
soil, from the disintegrated basalt, has been moulded by the ac-
tion of wind and water into a dune-like topography (Fig. 38).
Because of the constant shifting of the soils from the exposed
south and southwest to the leeward slopes, the latter are much
steeper. These hills reach a height of Ioo to 360 feet. Measure-
ments of a large number of slopes near the base station gave an
average gradient of I2° on the exposed sides, while the sheltered
sides were from 5° to 8° steeper. Indeed, in parts of the region,
many of the hillsides are so steep that they can not be brought
under cultivation. The intervening valleys are usually narrow,
but never form undrained basins. The general slope of the
region is westward. While Thatuna Hills, a low, outlying spur
of the Bitterroot Mountains, culminate in Cedar Mountain, 4,950
feet high, the eastern edge of the lava sheet reaches an altitude
of only 2,750 feet (Fig. 1). It descends at the rate of about 30
feet per mile, to 1,170 feet on the western border of the region
under consideration. *
Two main rivers with their tributaries drain the region except
the northeastern part which is drained by tributaries of Spokane
River. The Palouse River has its headwater tributaries in the
mountains of Idaho, and after passing into Washington the north
and south forks unite at Colfax. In the western part of the
region it turns southwestward and finally enters the Snake River.
At Colfax the river has cut a canyon into the basalt to a depth of
300 feet. -
In general, the river canyons, whether large or small, are char-
acterized by much steeper south and southwest than north and
northeast banks. This is due in part to greater exposure of the
north and northeast sides to temperature changes, and to wind
action which erodes and carries away the soil materials, and in
part to the constant covering of the sheltered sides by wind-
blown material. These processes have a striking effect upon the
vegetational cover. Locally the exposed canyon walls are known
as rim-rock.
Snake River is joined by the Clearwater as it enters Washing-
ton. Tributaries of the latter drain the extreme eastern part of
9
IO A Study of the Vegetation of
the region. Snake River flows westward through the region in a
canyon which is simply an immense gorge a mile and a half to
two miles wide hewn in the basalt. Although the canyon is
over 1,600 feet deep, the river has not yet, except in a very few
places, cut to the bottom of the basalt, for its present bed is still
like its bluffs. The soil of these bluffs, as is characteristic of
similarly exposed situations in the region, presents various stages
of decomposition from the coarse talus at the foot of the cliff to
well formed soil. The canyon at its bottom is scarcely wider
than the river, except at the bends, where bars of moderate area
have been formed. The soil of the bars is partially river-sand
of granitic origin and partially wash from the bluffs.
Except for the Clearwater, no large streams enter Snake River
in this region. Numerous small laterals have worked their way
back into the basalt, and it is along these that the main canyon
may be entered, especially from the south.
In general, the topography is young. The streams have not
advanced far in their task of cutting away the rocks from the
plateau and of reducing the land to base level. Especially south
of Snake River, in Garfield County, where the surface is less roll-
ing, one is impressed with the view of a land with a broad plateau
surface and an infantile drainage. Here the spaces between the
streams are flat-topped. -
In the northwestern part of the area occur numerous small
lakes, of which Rock Lake, about O.5 mile wide and 7 miles long,
is the largest. It is really a great crack in the basalt, with rocky
canyon walls and basalt bottom. It connects northward with
Little Rock Lake and is drained into the Palouse River by Rock
Creek.
About these lakes, as well as along the canyons of the streams,
the weathering of the edge of the basaltic sheets has caused them
to recede unequally and to form steps or terraces in the faces of
the precipices. Where the walls are steepest, they present a
series of narrow steps covered with talus and soils in all stages of
formation, separating vertical masses of bare and frequently
columnar rock 30 or more feet in height (Fig. 45).
In the drier western part of the region, where the disintegra-
IO
Southeastern Washington and Adjacent Idaho. I I
tion of the basalt is correspondingly of a smaller degree, the rock
often crops out upon the surface. Such rocky lands are known
locally as scab-lands. They often occupy what appear to be for-
mer river valleys, although they are now dry or contain only small
streams or small groups of lakes. These valleys may be of con-
siderable extent; the local names, “Eight-mile Flat,” “Twelve-
mile Flat,” etc., indicate their size.
Owing to the porous nature of the basalt, as well as to sheets
of clay, sand, and gravel interspersed between the successive
layers, springs are numerous throughout the region. Oftentimes,
wells dug merely into the soil afford a good supply of water,
although they are usually drilled into the basalt (8). In other
cases, as at Pullman, an abundant supply of fine artesian water
is obtained from beds of sand and gravel between the layers of
basalt.
Standing above the surrounding plateau are numerous isolated
buttes and several ranges of low mountains. These are the tops
of lofty mountains not overwhelmed by the flood of basalt.
Among the former, Steptoe Butte, a perfectly eonical peak with
an altitude of 3,613 feet, is a landmark to be seen for miles.
Likewise, Kamiak Mountain, running from east to west for a
distance of over two miles, and reaching an altitude somewhat
greater than Steptoe Butte, is equally prominent. In some cases,
only a few acres of the tops of buried mountains show them-
selves above the basalt. Such a butte may be seen just west of
Bald Butte, the culmination of a ridge of quartzite running out
southwestward from Thatuna Hills. Tekoa Mountains, near
Tekoa, Washington, are a low, outlying ridge of the Bitterroot
system. They reach a height of 4,000 feet. Gold Hill, not far
from Potlatch, Idaho, is the highest point (about 4,500 feet) of
another group, while Cedar Mountain (4,950 feet), northwest of
the Clearwater River in Idaho, is the highest point of a consider-
able range known as Thatuna Hills. These buttes and mountains
are very old geologically as compared with the basalt, and are
well eroded and mostly forest-covered. Southeastward their
streams empty into the Clearwater River. Elsewhere they are
I I
I 2 A Study of the Vegetation of
drained by the Palouse River and in the extreme northeast by
tributaries of Spokane River (Fig. 1).
GENERAL PLANT—LIFE CONDITIONS
Hemmed in on all sides by mountains the region under consid-
eration has a climate much warmer and much drier than one
would expect at this altitude and latitude. The Okanogan High-
lands on the north shelter it from cold winter winds, while on the
east and south it is protected by the Bitterroot Mountain system
and the Blue Mountains, respectively. The Cascades on the
west intercept the rain-bearing westerly winds from the Pacific
Ocean. Even where the prevailing southwest wind cutting
through the mountain gap of the Columbia River and rising over
the high plateau drops much of its moisture near the high eastern
border, the annual precipitation is only 21.6 inches. Westward
it decreases steadily with decreased elevation, giving an annual
precipitation of only IO-13 inches near the western boundary of
the region. * -
In this semi-arid region where evaporation rates are very high,
a knowledge of the distribution of rainfall and humidity is very
important, for it is well known that scanty rainfall throughout the
year, or relative dryness of the air and soil during the growing
season, favors a sparse vegetation and the development of xero-
phytic forms. Since vegetation is not only an expression of
present conditions, but to a greater extent a record of conditions
that have obtained during a period of years, and since the record
is not likely to be altered by a year or two in which conditions
may depart from the normal, a study of the precipitation in Fig.
2 is instructive. This gives the mean monthly precipitation at
Pullman, covering a period of twenty-four years, and is very
representative of conditions in the high prairies. It may be seen
at a glance that over two thirds of the precipitation occurs dur-
ing the non-growing season, and that the light showers of July
and August seldom have much influence upon the water content
of the soil. -
In order that the reader may realize the striking difference be-
I 2
Southeastern Washington and Adjacent Idaho. I 3
tween the distribution of rainfall of this region and that of the
Great Plains east of the Rocky Mountains, Fig. 2 also includes
the average monthly rainfall at North Platte, Nebraska. It also
gives the precipitation at La Crosse, a station in the western part
of the region. *
However, it is not the absolute rainfall figures alone which
furnish a criterion of climate, for the maximum duration of the

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FIG. 2. Mean monthly precipitation in inches at Pullman and La Crosse,
Washington, and North Platte, Nebraska.
drought period constitutes a limiting factor of the greatest im-
portance.
During the dry summer months the sky is usually cloudless.
At the base station the number of clear days during the growing
season (April–October) was 68 per cent. for the years 1914 and
I915. Bright, warm days are followed by cool nights. In fact,
a notable feature of the temperature of the region is the great
variation between day and night temperatures, especially in sum-
mer, when a variation of 20° to 40° F. is not unusual. These
cool nights naturally indicate rather late frosts in spring, and
early ones in autumn. On the plateau, killing frosts not infre-
quently occur as late as the middle of May, and, of course, much
later in the mountains. In the fall they may occur as early as
the middle of September, although light frosts sometimes occur
in August. The winters are mild and the prairie soils seldom
I 3
I4. A Study of the Vegetation of
freeze deeper than 4–6 inches. The snowfall normally is about
46 inches. The mean monthly and annual temperatures at the
base station are given in Table I. It is interesting to note that the
mean annual isotherms are approximately the same as those of
eastern Nebraska. These are 52° F. to 47° F. These figures
do not include the canyon of the Snake River, which has a dis-
tinctly warmer and drier climate. - -
TABLE I
TEMPERATURES AT PULLMAN, WASHINGTON

# | || 5 || 3 | #| 3 | } §
t; 3 | *
d z c |<
à
;
#
Mean daily maximum. . . . . . . 35 | 36||47 || 56 63 | 72 83 83 || 70 56 || 42 35 | 56
Mean daily minimum. . . . . . . 22 24 3I |37 || 43 |50 55 54 |46 ||38|31 || 24 || 38
Mean. . . . . . . . . . . . . . . . . . . 29 |32 ||38||47 | 53 59 | 67 | 66 58 49 38 |32 || 47
Since it is not the mean temperature of a region but rather the
extremes that exert the most profound effect upon plants, Table
I also includes the mean daily minimum and mean daily maximum
temperatures.
Another important climatic factor is the wind. It is prevail-
ingly from the southwest. Just as it has had such a profound
effect upon moulding the topography of the region, likewise it
has a marked effect upon the vegetation. Sweeping across the
many miles of open prairie and desert of northern Oregon and
South-central Washington, and not infrequently attaining a
velocity of 30–50 miles per hour, it has a marked effect upon
the evaporating power of the air. By increasing the latter, it
increases the saturation deficit and consequently accelerates
transpiration. During the growing seasons of IQI3–1914, the
wind blew from the southwest, or some southerly or westerly
direction over 60 per cent. of the time. The southwest winds
often assume the form of dust storms in summer. For days the
air may be so filled with dust that the sun is scarcely visible.
Such storms may become serious enough to cause much destruc-
tion. -
Because of the deficient rainfall and the low humidity through-
I4. -
Southeastern Washington and Adjacent Idaho. I 5
out the region, the vegetational distribution is markedly influ-
enced by the edaphic and topographic conditions. The influence
of rainfall upon the distributional and seasonal activities of plants
is obviously exerted chiefly through its power to replenish soil
moisture. While rainfall is only indirect in its relation to plants,
soil moisture is direct. The retention of moisture by soil de-
pends not only upon the kind of soil, but also upon the slope and
exposure. These regional differences in precipitation, together
with topography and soil depth, delimit in a more or less definite
manner the plant communities.
It may make the situation somewhat clearer if, before taking up
a detailed discussion of the structure and development of each
vegetational unit, a brief survey of the chief plant groups in the
succession is given.
GENERAL VEGETATIONAL DISTRIBUTION
The Festuca consociation of the Agropyron-Festuca associa-
tion occupies the extreme eastern rim of the basaltic plateau, in-
cluding the lower buttes and the exposed southwest slopes of
some of the higher buttes and mountains (Figs. 21 and 22). This
community extends from the yellow pine consocies of the Spo-
kane gravels southward beyond Snake River. It occupies the
part of the plateau having the deepest soils and the highest rain-
fall. Eastward it reaches to Tekoa Mountains, Thatuna Hills,
and other outlying spurs of the Bitterroot system. The breadth
of this belt is variable, depending upon the precipitation and soil
moisture. Perhaps at no point does it exceed 40 miles. West-
ward and southward it merges into the Agropyron consociation
(Figs. I9 and 20). -
In the Festuca consociation, besides the blue bunch-grass (Fes-
tuca ovina ingrata) and Balsamorhiza sagittata, Agropyron spica-
tum (including variety inerme) is the most important component
of the plant cover. In marked contrast to its bunch habit in the
consociation bearing its name, in the more mesophytic Festuca
community it is often a sod former. Other important grasses are
Koeleria cristata and Poa sandbergii, while numerous composites,
legumes, and other herbaceous species are abundant. Many of
I 5
I6 A Study of the Vegetation of
these do not occur in the Agropyron community, while indeed
several species are confined to the moist north hillsides occupied
by this consociation.
At lower altitudes westward and southward the well developed
prairie gradually merges into the Agropyron consociation. Like-
wise, on the rim-rock along the canyons of streams as well as on
dry mountain slopes this community is well represented. It is
characterized by the definite bunch habit of its chief species Agro-
pyron spicatum. These bunches are often more than 8 inches
in diameter, and may reach a height of over 3 feet. In addition
to the absence of numerous characteristically high-prairie species,
and the more open nature of the plant cover, the Agropyron con-
sociation is further characterized by the coming in of certain
plants of a more xerophytic stamp. Most conspicuous among
these are the rabbit brush, Chrysothamnus nauseosus (including
var. graveolens), C. viscidiflorus, and several species of Erio-
gonum. The bunch-grass not only occupies the deeper soils of
the drier region, but is represented in the scab-lands and on the
rim-rock where the soils, only a few inches deep, overlie deeply
fissured basalt.
On the unbroken rock, covered with only an inch or two of soil,
Agropyron gives way to the Poa-Polygonum associes, a still earlier
stage in development (Fig. 18). This latter associes is well rep-
resented on the rim-rock throughout the region, as well as over
large areas of the scab-lands westward. The June grass, Poa
sandbergii, Polygonum majus, and Plantago purshii, are the most
important species. The knotgrass and plantain play the rôle of
grasses ecologically. This associes is preceded in the succession
by communities of mosses and lichens (Fig. 17).
In the driest part of the region, in the scab-land, where the
basalt is almost free from soil, occurs the extreme eastward ex-
tension of the desert scrub formation. It is represented by the
Artemisia-Atriplex association of which Artemisia rigida, the
scab-land sage of the Artemisia consociation, is the characteristic
species (Fig. 16). In the deeper soils impregnated with alkali
the greasewood consocies, dominated by Sarcobatus vermicu-
latus, occurs.
I6
Southeastern Washington and Adjacent Idaho. I7
On the more mesophytic slopes of the treeless hills of the well
developed prairie a poorly developed shrub associes occurs. This
is made up of Symphoricarpos racemosus, Rosa nutkana, R. piso-
carpa, dwarfed specimens of Prunus demissa, Crataegus brevi-
spina, Amelanchier spp., and sometimes Opulaster pauciflorus,
and small trees of Populus tremuloides. These shrubs are better
developed in the canyons and are usually forerunners (especially
Opulaster pauciflorus) of the yellow pine; along the stream
margins they give way to the flood-plain forests of Populus,
Crataegus, Amelanchier, Salia, and Alnus (Fig. 35).
On the outlying buttes as well as in the mountains, the Opu-
laster consocies often occupies considerable areas between the
pines and the grass land (Fig. 23). It almost invariably occurs
on the sheltered sides of lower buttes and mountain ridges, while
its presence as a half-dead relict under the pioneer forest indi-
cates its former possession of numerous other situations.
The Prunus consocies is less abundant than the preceding, but
it is well represented in dry situations on butte and mountain
sides. Like Opulaster, it is replaced by the pines in the normal
succession. The chief species is the shrub-like tree, Prunus
emarginata.
On the higher mountains especially, the Ceanothus consocies
plays a rôle similar to the other shrubs of this associes. The two
species C. velutinus and C. sanguineus, of which the former is
the more important, act as forerunners for the yellow pine and
Douglas fir. {\
The Pinus consocies is represented by the western yellow pine,
Pinus ponderosa, the most xerophytic forest tree in the region.
This consocies not only occupies dry slopes and ridges on the
buttes and mountains, but has worked down along the Palouse
River canyons as well as along Rock Lake and Rock Creek and
Union Flat, to an altitude of only 1,500 feet (Figs. I, 24, and 45).
Everywhere the pine is the pioneer forest tree, and forms a fring-
ing belt along the prairie. While it is usually preceded by some
shrub consocies, yet it is able to invade the prairies, and especially
those with a more sandy soil, without such an intervening stage.
The Pseudotsuga consocies, when pure, occupies dry, rocky
17
I 8 A Study of the Vegetation of
slopes of the higher mountains, such as Gold Hill and Cedar
Mountain. More usually Douglas fir is mixed with yellow pine,
it being only slightly less xerophytic than the latter. Such mix-
tures of pine and Douglas fir frequently occupy large areas, the
dominance of the latter indicating more mesophytic conditions
(Fig. 25).
The Larix-Abies associes forms the chief forests of the region.
The western larch, Larix occidentalis, being more xerophytic than
the white fir, Abies grandis, is usually the first tree to appear
in the Pseudotsuga consocies. Mixed forests of Douglas fir and
larch are not infrequent. These often show relict pines and in-
vading white firs. Such exposed situations as Kamiak Moun-
tain and Tekoa Mountains are especially representative (Figs. 37
and 46).
Likewise, large areas of sheltered mountain slopes are charac-
terized by Larix and Abies in nearly equal abundance, with a
considerable admixture of Douglas fir on the drier slopes and
the appearance of cedar, Thuja plicata, in the moist ravines (Figs.
26 and 27). Finally, in the deep ravines and most sheltered situa-
tions, the giant cedar, representing the climax community of the
region, appears. Often it forms pure stands over local areas,
the low light intensity excluding other trees (Fig. 28). But more
frequently it forms a mictium with the white fir and larch, Abies
being the last to drop out. -
Each stage in forest succession is characterized by its particu-
lar group of shrubs and herbaceous vegetation. The story of
succession from one stage to the next is largely a story of in-
creasing water content and of decreasing light.
Perhaps this brief survey, together with a glance at the map
(Fig. I), will enable the reader to grasp the general vegetational
regions. Following is an outline of the units of vegetation and
their subdivisions in the order of their development.
The developmental basis for the analysis of vegetation as set
forth by Clements (2) is adopted here. Such a basis includes
physiognomy, floristics, and habitat. For those who are not
familiar with this basis of classification a few words of explana-
tion may not be amiss.
I 8
XEROSERE BIYDROSERE
Pacific Coast Forest Formation
Thuja-Tsuga Association
Thuja Consociation (Fig. 28)
Laria-Abies Associes
Larix-Abies–Thuja Mictium (Fig. 27)
Pseudotsuga–Laria-Abies Mictium (Figs. 26 and 37)
Pinus-Pseudotsuga Associes •
Pseudotsuga Consocies (Fig. 25). `alusai. Associes
Pinus Consocies (Fig. 24)
Symphoricarpos-Opulaster Associes
Ceanothus Consocies
Flood-plain Forest Associes
Opulaster Consocies (Fig. 23) N Populus Consocies
Prunus Consocies Salia-Crataegus Mictium (Fig. 35)
Symphoricarpos-Rosa Mictium -
Prairie-Plains Formation (Subclimax)
Agropyron-Festuca Association –Wet Meadow Associes
Festuca Consociation (Figs. 21 and 22) 4–T | Deschampsia Consocies
: Agropyron Consociation (Figs. Ig and 20) Wyethia Socies
Poa-Polygonum Associes (Fig. 18) - Heracleum Socies (Fig. 34)
Polygonum Consocies Iris Socies (Fig. 33)
Plantago Consocies . Quamasia Socies (Fig. 32)
Poa Consocies - Eleocharis-Carear Associes
Grimmia-Tortula Associes (Fig. 17) Carea-Juncus Mictium
Tortula Consocies Eleocharis Consocies (Fig. 31)
Grimmia Consocies Scirpus-Typha Associes
Gyrophora-Parmelia Associes (Fig. 17) Typha Consocies
Parmelia Consocies Scirpus Consocies (Fig. 31)
Gyrophora Consocies Nymphaea-Potamogeton Associes
Rhigocarpon-Lecidea Associes (Fig. 17) Potamogeton Consocies (Fig. 29)
Lecidea Consocies Nymphaea Consocies (Fig. 30)
Rhizocarpon Consocies Chara-Potamogeton Associes
Desert Scrub Formation (Subclimax) Potamogeton Consocies
Artemisia-Atriplear Association Chara Consocies
Artemisia Consociation (Fig. 16)
C


o
20 A Study of the Vegetation of
The formation is the unit of vegetation. It is the climax com-
munity of a natural area in which the essential climatic relations
are similar or identical. It is an organic entity, covering a defi-
nite area marked by a climatic climax. It consists of associations
which are actual parts of the area with distinct spatial relations.
The term association is restricted to those climax communities
which are associated regionally to constitute the formation. As-
sociations agree with their formations in physiognomy and devel-
opment and are recognized chiefly by floristic differences.
The consociation is the unit of the association. It is charac-
terized by a single dominant. While the association is actually a
grouping, the consociation is pure dominance. In the usual treat-
ment, most consociations appear as associations.
A society is a community characterized by one or more sub-
dominants, that is by a species dominant over portions of an
area already marked by the dominance of consociation or associa-
tion. It is a localized or recurrent dominance within a dominance.
The above units of vegetation are essentially climax. The fol-
lowing are developmental. To ecologists who regard the forma-
tion as an actual organism, it is essential to distinguish develop-
mental and climax communities. -
The associes is the developmental equivalent of the association.
It is composed of two or more consocies, i. e., developmental
consociations, just as the association consists of two or more con-
sociations. Like the association, it is based upon life-form,
floristic composition, and habitat, but differs from*t in as much
as all of these are undergoing constant or recurrent developmental
changes. While the association is permanent, in so far as de-
velopment is concerned, the associes is transient although it may
persist for many years.
A consocies is a developmental community marked by the strik-
ing or complete dominance of one species belonging to the life-
form typical of that stage of development. It differs from the
consociation only in that it is a developmental or seral, while the
latter is a climax community. -
A socies is a seral society characteristic of a developmental
2O
Southeastern Washington and Adjacent Idaho. 2 I
community instead of a climax one. Like the society it is a case
of subdominance within a dominance.
The following table shows the relation of climax and seral or
development units to the formation, as well as the relation of
the units of each series to each other and the correspondence of
units in each series.
FORMATION
Climax Units: Seral Units:
Association Associes
Consociation Consocies
Society Socies
EVAPORATION AND SOIL MOISTURE IN RELATION TO
SUCCESSION
Without question, the water relations of the habitat are the
most important cause of succession. This is especially true of
grass land communities, and even in forests where light is a con-
trolling factor, it is well known that the water relation has a
marked effect upon the tolerance of forest trees. As Fuller (4,
5) has pointed out, in a study of water conditions, two phases
of the subject are of importance.
They are the direct source and amount of the supply and the region
and cause of the loss. The latter is a climatic, the former largely an
edaphic problem, for it is evident that plants derive their moisture from
the soil and lose it into the air, and for the quantitative solution of these
problems it is necessary to measure the power of the air to extract water
from the plant; in other words, the evaporating power of the air, and the
amount of moisture in the soil available for the use of plants.
Fuller (4, 5) and others have pointed out that the evaporation
rates in the lower ačrial stratum and the range of water content
in the upper subterranean stratum are the most critical ones.
Within this (aërial) stratum develop all the seedlings, and upon their
death or survival depends the character of the succeeding vegetation.
Therefore, if the vegetation of an association so affects the evaporation
rate of this stratum that it permits the survival of seedlings of more
mesophytic species, it is evident that a more mesophytic association will
develop, and succession will be accomplished.
Measurements of the water content of the soil and the evap-
2 I
22 A Study of the Vegetation of
orating power of the air have been carried on in the various plant
communities and a relation has been established between the mois-
ture conditions and plant succession.
Livingston's standardized porous cup atmometers were used to
determine the rate of the evaporating power of the air. They
were always placed with the evaporating surfaces 17–23 centi-
meters above the surface of the soil, care being taken in all cases
to select spots which possessed the average amount of herbaceous,
shrubby, or tree vegetation characteristic of the community as a
whole. These cups were almost invariably run in duplicate,
sometimes in triplicate; they were frequently checked and re-
standardized, and the readings reduced to those of the standard
atmometer. In the following graphs, the ordinates give the aver-
age daily evaporation during the intervals indicated by the ab-
scissas. A preliminary report giving a detailed statement of a
part of these results has already been published (16).
Soil moisture determinations were made at the same stations
and at the same time that evaporation readings were taken. In
making the determinations, samples of IOO–150 grams were in-
variably taken in duplicate and from separate holes about 3 feet
apart. These samples consisted of a core of soil to a depth of IO
inches. They were dried in an oven at a temperature of Ioo-
Io5° C. and the water content calculated in percentages on the
basis of the dry weight.
In the following figures, the results are represented graphically,
the wilting coefficients being shown by lines of the same type as
the line showing the range of soil moisture for a particular com-
munity. The ordinates represent the percentages of soil mois-
ture and the abscissas indicate the intervals between readings.
The intervals between the graphs and the lines denoting the wilt-
ing coefficients (if these exist above the latter) give the amount
of available water.
During the summer of 1913 a group of stations were estab-
lished near Colfax, Washington. Here the south fork of the
Palouse River has cut a canyon in the basalt to a depth of 300
feet. Along the north bank of this canyon the Agropyron con-
sociation is well developed. The sheltered south bank is covered
22
Southeastern Washington and Adjacent Idaho. 23.
with a consocies of yellow pine, above which, and still on the
north slope, the Festuca consociation continues. The atmometers
in the Agropyron community were installed about half way up
the bank of the canyon. Those in the pines were placed in a

//57) || |yo//vº | Jazz r | #46437 || 5
l
#2 rzyrszkº -T – -- - - -"
34 ſesſwho copsoc/ yon.
P/203 corºdoc/es —— — —l— —
Q / Z– L-IT
/, /
5 4–4
Z||\LL/ / /-E-F-F-T,
5 * Y
Z} ( / /
ſo | N /
, - N —" Af
4-1-1 SSN- /
FIG. 3. Evaporation rates in the Agropyron, Festuca, and Pinus communi-
ties at Colfax, Washington.
similar position on the opposite bank, and about 60 feet beyond
these a station was established in the Festuca consociation.
Graphs of the data from these instruments have been plotted in
Fig. 3.
These graphs show a striking decrease in the evaporating power
of the air as the progressive stages of vegetational development
are approached. During IQI2 preliminary measurements indi-
cated just such conditions in these communities. Stations main-
tained at Pullman during 1913, showed similar differences in
evaporation between the Agropyron and Festuca consociations,
while during 1914 further data at Colfax confirmed in general
the above results.
23
24 A Study of the Vegetation of
Fig. 4 shows the comparative average daily evaporation rates
during 1913 in the three communities, respectively. These data
#7. proºfonsor Ž7,
s Zaz (d2s2&722
AE/P//5 ca.7soches
FIG. 4. Average daily evaporation rates in the Agropyron, Festuca, and
Pinus communities during IQI3. .
are averages of six stations located in the several communities.
The water content of the soils at the preceding stations at Col-
fax is indicated in Fig. 5. A glance shows that the soils covered
by the Agropyron consociation had at all times the lowest avail-
able water content. Those of Pinus and Festuca communities
are approximately the same, and indeed this condition has been
found to exist elsewhere in several similar situations. Isolated
determinations at the same stations at various intervals during
the following season showed a similar water content relationship.
Y cy///// J(/ſ y A///6 (/5 &
FIG. 5. Graphs showing the march of soil water to a depth of Io inches
in various plant communities at Colfax, Washington.





24
Southeastern Washington and Adjacent Idaho. 25
But the soil water reached its non-available point somewhat ear-
lier. However, the Agropyron consociation was the first to ex-
haust its available supply.
The enormous strain brought to bear upon these early develop-
mental plant communities may be realized when it is noted that
after the water of the first Io inches of soil became unavailable,
the evaporation throughout the remainder of the season was very
high. Two methods of meeting these adverse conditions are em-
ployed by plants of these communities. They either mature early
and become dormant upon the approach of drought, or develop
very extensive root-systems. But these had best be discussed
under structure and development of vegetation.
The mechanical analyses of these soils show that those of the
Agropyron consociation are of a coarser texture than those of
the Festuca consociation (Table II). Likewise the humus and
volatile matter were found to be lower in the former.
TABLE II
MECHANICAL ANALYSEs OF SOILs FROM VARIOUS PLANT Communities IN
SouTHEASTERN WASHINGTON AND ADJACENT IDAHO
jºkºlºr:#|##| #| | | Sº,
Station ove | 2.3 Jº | Sand O.25 Sand O.O5 O.OO5
*22 to Jolto oso.o.5o to oro o-ro |*.*.*5|*ºoo
Mm. | M. M. to 5.25. M. to o.o.5 Mm. | Mm.
º II]. Mm.
Agropyron consociation, Col-
fax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.40 | I.OO | I.80 || 34.48 || 54.20 7.04
Festuca consociation, Colfax | . . . . . . . . . . .80 | .40 | .40 || 23.30 | 66.00 9.oo
Festuca consociation, Ka- .
miak Mt. . . . . . . . . . . . . . . .68 .40 | I.40 | .42 || 5.80 26.80 || 54. Io | Io.83
Pseudotsuga–Larix commu- -
nity, Kamiak Mt. . . . . . . . .60 | . . . . . .I2 | .40 | I.72 21.60 | 61.80 || 4:34
Thuja consociation, Cedar
Mountain. . . . . . . . . . . . . . 6.08 .62 | 3.60 I.60 | 3.60 | 2I.65 57.60 | 5.7o
Pseudotsuga–Larix-Abies
community, Cedar Moun-
tain. . . . . . . . . . . . . . . . . . . . 3.56 | 1.04 || I.52 I.08 || 7.82 25.37 || 55.40 || 4.18
Festuca consociation, North- -
east slope, Pullman. . . . . . . . . . . .40 | .40 | .90 I.50 | 33.16 53.5o | Io.03
Festuca consociation, South- - -
west slope, Pullman... . . . . . . . . . . . . . . .60 | .60 | .40 || 23.58 | 73.30 | I.49
25
26 A Study of the Vegetation of
A chemical analysis not only confirms the low amount of vola-
tile and organic matter, but also shows, as one would expect, the
low nitrogen content of the new soil covered with bunch-grass
(Table III).
TABLE III
CHEMICAL ANALYSES OF SOILs FROM VARIous PLANT Communities IN
SouTHEASTERN WASHINGTON AND ADJACENT IDAHO

Phos- So- || Total Vola-
Lime, Pot- |phoric Soda dium | Soul tile and Insolu-| Hu- |Total
’ ash, Anhy-|Ash, Tri- Or- ble Nitro-
CaO * - ble - - IIlliS
K2O dride, |Na2O oxide, | Salts ganic |Matter gen
P2O5 SO3 Matter
Agropyron consocia-
tion, Colfax. . . . . . I.08 O.58 || 0.31 I.32|0.034. Iş.02| 5.35; 79.63| I.06 || 0.096
Festuca consociation,
Colfax. . . . . . . . . . . I.27 O.54 || 0.29 || 0.47 0.037. I3.77| 6.32| 79.91 2.88 |O.I.76
Festuca consociation, -
Kamiak Mt. . . . . . I.03| 0.45 | O.29 |0.06| 0.047. I3.5ol 5.95 80.55| 2.77 O.I.82
Pseudotsuga – L a r i <
community, Ka- -
miak Mt.... . . . . . . . o.85io.32 o.41 jo.41| O.030. I2.73| 4.95 82.32 I.I2 o.o.8I
Thuja consociation, |
Cedar Mountain. . . I.I.7| 0.23 0.59 || 0.07| O.O75|| I4.77| I3.65 71.58| 6.39 O.399
Pseudotsuga-L a r i <-
Abies community,
Cedar Mountain. . . o.52] O.23 O.33 O.O3|O.O44 I.4.62| 8.76 º 3.45 || O.2O7
A second set of stations was maintained on Kamiak Mountain,
a bold butte lying 9 miles north of Pullman, and one of a series
extending in a westerly direction from Thatuna Hills. This
butte running from east to west for a distance of over 2 miles,
and reaching an elevation of 1,000 feet above the surrounding
hilltops, is covered on the south side with prairie, while the
steeper north slope bears a dense forest of Douglas fir and west-
ern larch (Figs. 36 and 37).
On the south side trees occur only near the summit, where out-
cropping rocks furnish in their crevices a sufficient shelter and
water supply for the establishment of the seedlings. Here is a
very open growth of yellow pine which flanks the fir and tamarack
and also occupies the less sheltered north base below the fir–
tamarack community. In fact, this mountain offered so many
interesting conditions of slope, exposure, and vegetational cover,
that I3 stations were maintained here during 1913.
26
Southeastern Washington and Adjacent Idaho. 27
Eight miles east, near Viola, Idaho, on another butte slightly
lower than Kamiak, but with plant communities very similarly
distributed, records from a third set of stations were obtained.
Here again the south side is prairie, which the pines, occupying
the crest and northwestern slope, are gradually invading. The
sheltered northeast side is clothed with a forest of Douglas fir and
tamarack. These conditions are representative of numerous
other situations (Fig. 46). Only as the mountains become higher
and rainfall increases, does the prairie give way to a forest
growth. The prairies at Kamiak and Viola are not greatly un-
like those upon the basalt as far as kinds of species and their dis-
tribution are concerned, but, because of differences in soils and
greater exposure to the wind, the vegetation bears a more xero-
phytic stamp and there are fewer plants per given area, and con-
sequently more soil surface exposed.
Fig. 6 gives the evaporation rates in the various plant com-
munities on Kamiak Mountain, and also that of the pine con-
socies at Viola, Idaho. A glance at the chart shows at once a
direct relation between the evaporating power of the air and the
stage in succession. The station on Kamiak in the Festuca con-
sociation was on a south slope and only about 60 feet below the
edge of the pines. The station in the pines was in a decidedly
xerophytic habitat, as is shown by the evaporation graph, which
closely follows that of the prairie. The ground was covered with
pine needles which almost excluded undergrowth and the at-
mometers were shaded only indifferently by the open growth of
the trees. The evaporation data in a more typical yellow pine
habitat located on the northwest slope of the butte at Viola is
plotted on the same chart, for the sake of comparison. It corre-
sponds in general with evaporation records secured from a second
station in the yellow pines located at the north base of Kamiak
Mountain, but from which complete data were not obtained.
Two stations were maintained in the shrub community. One
of these was located on the south side of the mountain and on a
northeast slope which was occupied by a very typical consocies of
Opulaster pauciflorus, into which the pines were invading. The
evaporation graph is given in the chart. It may be noted that
27
28
A Study of the Vegetation of
this station was intermediate in xerophytism, as expressed by the
evaporating power of the air, between the two. stations in the
pines.
A second station in the shrub on the north slope of the
butte and near the western end was maintained in a dense growth

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FIG. 6. Evaporation rates in the various plant communities on Kamiak
Mountain, and in the Pine consocies (graph 4) at Viola, Idaho.
of Opulaster-Ceanothus chaparral. The evaporation rates, not
shown in the chart, were much lower, often being less than those
in the fir-tamarack forest.
In fact, it is not difficult to find situa-
tions in which shrubby growth is so dense as to greatly retard
evaporation and reduce the light to a point where pine seedlings
can not grow.
28
Southeastern Washington and Adjacent Idaho. 29
The station in the firs and tamarack on the north slope of the
mountain and only about 60 feet from the top, was in a forest of
nearly pure second growth Pseudotsuga and Larix. These trees
are mostly about thirty-five years old and are equally distributed,
with a few relict pines and about three per cent. white fir. It
may be noted that the graph of evaporation here is decidedly
lower than in any other habitat.
/7 (///
FIG. 7. Graphs showing the march of soil water to a depth of Io inches
in various plant communities on Kamiak Mountain.
The evaporation stations at Viola gave results comparable to
those shown on the chart for Kamiak. Without exception, the
average daily rate of evaporation in the prairie on the southwest
slope was higher than that of the pines on the northwest slope.
Likewise, the graph of evaporation in the fir-tamarack forest
showed a continuously lower rate than that in the pines.

29
3O A Study of the Vegetation of
At the stations on Kamiak Mountain where evaporation data
were obtained, water content samples were taken at the same
intervals of time. These data have been plotted in graphic form
in Fig. 7. The water content of the soils of the pine consocies
was obtained from the station at the north base of the mountain,
that of the shrub from the Opulaster consocies on the northeast
slope. The gradual depletion of the water content of these soils
to the end of the growing season is characteristic. To fully ap-
preciate the conditions represented on the chart, a description of
the soils is necessary.
. A mechanical analysis of the soils shows that those of the
prairie are somewhat coarser textured than those of the fir-
tamarack community (Table II). Likewise, a chemical analysis
of these two types of soil shows that among other differences
there is a markedly lower humus and total nitrogen content in the
soils of the forest (Table III). This is due to fires burning out
the organic matter.
The greatest difference in the soils, however, and the one which
most profoundly affects the vegetation in this semi-arid region is
their water holding capacity. An average of 6 tests showed the
prairie soils on Kamiak had a water holding capacity of 48 per
cent., while the finer soils of the north slope which support a
forest of fir and tamarack hold 78 per cent. of their dry weight
of water. The water holding capacity of the soil of the pine con-
socies was intermediate between the preceding. We may com-
pare the soils of this region to a gigantic reservoir replenished
mostly during the non-growing season and rather thoroughly
emptied of its water during the summer.
The actual amount of water available to the forest- and shrub-
covered soils of the protected slopes and ravines is often consid-
erably greater than that of the prairie. Snow is blown from the
wind-swept prairie and deposited on the sheltered slopes. I have
seen such drifts 20–25 feet deep along the brow of Kamiak Moun-
tain. The late melting of the snow makes a locally late spring
and consequently shortens the period of drought in late summer.
Soil samples taken on Kamiak Mountain in May and in July,
I914, bear out the conditions found in the previous year, but
3O
Southeastern Washington and Adjacent Idaho. 3 I
.*
here, as at Colfax, the available water was exhausted somewhat
earlier than in the summer of 1913. On July 14, 1914, and when
the available moisture of the surface ten inches had been depleted
in all habitats, samples were taken as usual at a depth of two
feet in the prairie and fir-tamarack communities respectively.
These showed that practically no water was available even at this
depth.
The relation of soil moisture to plant succession was likewise
determined at the stations already described near Viola, Idaho,
during 1913. The results are plotted in Fig. 8. These graphs
JUINE J /ſ/ Y Aſ Öſ
C
FIG. 8. Graphs showing the march of soil water to a depth of Io inches
in plant communities at Viola, Idaho.
appear somewhat different from those at Kamiak. This is due
in part to the longer intervals between readings. Also the fir–
tamarack station was somewhat less mesophytic than that at
Kamiak, but like the former, was covered with a second growth
of Douglas fir and tamarack. Likewise, the pine community was
of a much more open type than that on the sheltered base of
Kamiak Mountain. The water holding capacity of the soil at

3 I
32 A Study of the Vegetation of
this station in the fir-tamarack community was 60 per cent, that
of the prairie and pines about 45 per cent. On August I4, I9I4,
the water content at each station was found to be somewhat
lower than on the same date of the preceding year. Samples
taken to a depth of 3 feet in the prairie showed that all of the
available water had been used. Indeed, at this time, practically
all of the vegetation except Hoorebekia racemosa, Solidago mis-
souriensis, Carum gairdneri, and a few other serotinal bloomers
had dried up. An examination of the root-systems of numerous
prairie species shows, however, that many of them obtain water
at much greater depths than 3 feet (Figs. I5a, I5b, and 15c). In
the underlying rocky soil on this butte it is probable that consider-
able water was still available at this date. Because of the rocks, I
was unable to secure samples at greater depths than 2 feet in the
pine community, but these soils on August 13, 1914, were even
drier than those in the prairie. Likewise, the deeper soils in the
fir-tamarack community were very dry.
The close similarity in water content between the soils of the
prairie and pine communities is just what one might expect when
the latter consocies was still quite open and only small amounts
of organic matter had been added to the soil. There is a close
similarity between these graphs and those obtained at Colfax in
communities of about the same stage of development.
In order to determine the relation between the evaporating
power of the air and the water content of the soil in the cedar
community as compared with earlier stages in succession, a series
of stations was maintained on Cedar Mountain during the sum-
mers of IQI3 and IQI4. A station was maintained in an area of
the climax cedar forest which occupied a north slope and a ravine
through which flows a small stream. This forest is over 95 per
cent. pure cedar, mostly large trees from 2 feet to more than 3
feet in diameter. The rest of the trees are large white firs, most
of which are dead. The characteristic undergrowth of meso-
phytic shrubs and herbs need not be described here.
About 700 feet beyond the station in the cedars and occupying
a slope somewhat above the latter, a station in the fir-tamarack
community was maintained. The Douglas fir and tamarack are
32
Southeastern Washington and Adjacent Idaho. 33
the principal trees, but a considerable amount of white fir and
some spruce (Picea engelmanni) are also present. The under-
growth is rather sparse.
The evaporation in the cedar forest was always lower than that
in the preceding developmental communities. The data taken in
the cedars are shown in Fig. 9. Those of the other forest sta-
May || J/WE | July || Acus7 ||3
/7Sod/o/or *-*. |\
P/7 consocie; – + – H — | * - / \
ƺ £757f7a-Zºzr/77t"/7Z777
9/ PV / N \
.7/.4/4 confocofon --- + — / \
Ll-' NA2."
FIG. 9. Combined graphs showing the average daily evaporation rates
at all the stations in the prairie, pine, and fir-tamarack communities on the
buttes and mountains. The lowest graph gives the average daily evapo-
ration in the Thuja consociation.
tions are shown combined with all other readings taken in the
fir-tamarack forest. For the sake of comparison, the chart also
gives combined graphs showing the average evaporation rates in

33
34 A Study of the Vegetation of
the butte-prairie and yellow pine communities. These data show
a marked relationship between the evaporating power of the air
and the stage of succession. Fuller (4, 5) has determined a simi-
lar relationship for the plant consocies which culminate in the
beech-maple climax forest. It is interesting to note in this con-
nection that the evaporating power of the air in the Thuja climax.
forest is only slightly greater (o.5 c.c. daily in 1913) than that
of the beech-maple forest climax of the East.
In order to further check these results, evaporation readings
were taken again in the cedars and fir-tamarack on Cedar Moun-
tain during IQI4. To this series of stations was added one in a
very open yellow pine consocies on a wind-swept western slope.
The results are given in Table IV. -
TABLE IV
SHOWING THE AVERAGE DAILY EVAPORATION RATES IN THE PINE, FIR-
TAMARACK, AND CEDAR CoMMUNITIES DURING THE SUMMER of 1914

July 3–11 July 11–18 July 18–25 || 25-Aug. I Aug. I-7 || Aug. 7-14
Pines . . . . . . . . . . I9 C.C. 24 37 35 40 34
Fir-tamarack . . . . I3 c.c. I3 2O 2O 23 22
Cedars. . . . . . . . . IO C. C. IO I4. I6 I8 I7
A record of the water content of the soils at the stations in the
cedars and fir-tamarack on Cedar Mountain was kept from June
I4 to September 17, 1913. During 1914 this was repeated for a
period, and to this a record of the soil moisture at the station in
the pine community was added. The results are shown graph-
ically in Fig. Io. A glance shows that the cedars occupy by far
the most mesophytic habitat. The high wilting coefficient indi-
cates at once a fine textured soil with considerable organic matter.
A mechanical soil analysis (Table II) reveals just such charac-
teristics. This is in marked contrast to the coarse sandy loam of
the station in the pine. Likewise, a chemical analysis (Table III)
shows 13 per cent of volatile and organic matter in soils of the
cedar community, and 8 per cent. in those occupied by the firs
and tamaracks. The water holding capacity of these soils is re-
markably high. It was found to be over Ioo per cent. of their
34
sº-
Southeastern Washington and Adjacent Idaho. 35

C///ſ J' (ZAZ)^ //06//57 SAA7.
ON
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N \ Y---
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5 N \ -
nº N \\
O b *
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g Whdio consocio/o/7 –-|- —
40 N N %40 corsoch ſ
3á. \ N \
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—- – -- —— — — — — — — — — — — — —-
7. - —
10 - - - - - - --|--| = +------
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FIG. Io. Graphs showing the march of soil water in various plant com-
munities on Cedar Mountain.
3
5
36 A Study of the Vegetation of
dry weight. The chart shows that at no time did these virgin
forests of fir-tamarack or cedar exhaust all of the water in the
surface ten inches of soil. Likewise, samples at a depth of 2
feet on August 1, 1914, gave a water content of 66 per cent. and
I9 per cent. in the cedar and fir-tamarack forest respectively.
Similar determinations at 2 feet in the rocky pine-covered soils
gave a water content of about IO per cent., which is very near the
wilting coefficient. The slow growth and dwarfed appearance
of these trees reflect the unfavorable habitat conditions.
These studies on the evaporating power of the air and the
amount and range of soil moisture in different plant communities
may be briefly summarized. -
Evaporation at different stations within the same plant com-
munity exhibits variations similar both in character and degree,
and the variations in the rate of evaporation gradually become
less and less as the climax type of vegetation is approached.
The great amount of evaporation in the earlier stages of succes-
sion seems a sufficient cause for the xerophytic character of the
vegetation.
A study of the differences of the rates of evaporation in the
various plant communities shows that these differences are suffi-
cient to be important factors in causing succession, at least
through the earlier stages, where light does not play an important
rôle.” -
If sufficient light is available, there is no question but that
humidity of the air and the soil are the most important factors
1 While reading proof of this manuscript the recent paper by Gates came
to the writer's notice. (Gates, F. C. The relation between evaporation
and succession in a given area. Am. Journ. Bot., 4: I61–178, 1917.) As a
result of an investigation carried on at Douglas Lake, Mich., he concludes
that a decrease in evaporation is not a prerequisite to succession; lowered
evaporation being coincident with and not an antecedent to it. Gates
worked in a region with summer rainfall, where the average daily rates
of evaporation were low. The highest average daily summer evaporation
obtained on open ground was only 14.7 cc. Certainly his conclusions are
not applicable to a region of practically no summer rainfall and where, in
areas covered with bunch-grass, the daily evaporation rate for the whole
growing season averaged 28 to 37 cc., with the average daily rate for cer-
36
Southeastern Washington and Adjacent Idaho. - - 37
affecting the establishment of the different plant communities.
The progressive increase of the humidity of the habitat causes
a corresponding increase in the mesophytism of the plant associa-
tions. This change of plant population from the xerophytic to
the mesophytic type is a phenomenon called succession.
The evaporation rates and the amount of soil moisture in the
various communities vary in general directly with the order of
their occurrence in the succession, the climax community being
the most mesophytic in both respects.
SOIL TEMPERATURE IN RELATION TO SUCCESSION
The temperature of the soil gives in a general way a summation
of the heat factors of the habitat. It combines the effects of
direct insolation and radiation, cooling by the retention of snow
or by the evaporation of moisture, and variations in temperature
caused by the passage of currents of air. Since plant communi-
ties react directly on temperature, a large number of soil tempera-
ture readings were made in the various plant communities to de-
tain weeks in mid-summer, even in well developed prairie, reaching 64 cc.
(Gates highest evaporation rate on open ground for a single week is 21.6
cc. per day.) -
Students of succession should keep in mind that the evaporating power
of the air affects the possibility of water intake as well as water outgo.
High rates of evaporation rapidly deplete the surface soil of water as well
as desiccate the plant. Mesophytes can not establish themselves under such
conditions. It is only after a cover of xerophytes cuts down the great
evaporating power of the air in the stratum in which seedlings develop,
by shading and by inhibiting wind movement that mesophytic plants can
establish themselves. Mesophytes do not replace xerophytes in succession
until the reaction of the latter on the habitat is such as to make possible
the requisite conditions of soil and air humidity, i. e., a condition where
sufficient water is available in the soil and air, so that transpiration may
not exceed absorption. That evaporation is further reduced by the meso-
phytes is repeatedly shown in the preceding data. Conditions for plant
life are then less severe and even more mesophytic plants can establish
themselves and become dominant. .
This concept is in agreement with Fuller's conclusion, which he reached
after several years of study in the Chicago region (5). Further evidence
is brought forward in a recent paper dealing with the prairie-forest prob-
lem in Minnesota and Nebraska. (Weaver, J. E., and Thiel, A. F. The
Bot. Surv. Nebr., N. S., I : I-60, 1917.)
37
38 A Study of the Vegetation of
termine the relation between this factor and succession. Read-
ings at depths of 2 and Io inches respectively, were taken at the
same stations and at the same time that soil samples for moisture
determinations were secured. In addition to these a large number
of readings near the soil surface, in the soil surface, and at depths
of one and two feet respectively, were made from time to time.
Many of the temperature readings were made simultaneously, and
in all cases recorded the interval between the readings at the
various stations was so short that the error thus introduced is
almost negligible. This possible error was further reduced by
taking the readings in the various habitats at any set of stations in
varying sequence. te
An examination of these data shows almost uniformly a de-
crease in soil temperature as the climax communities are ap-
proached. The following tables, selected as representative from
these data, are illustrative:
TABLE V
SHowING THE RELATION OF SOIL TEMPERATURE to PLANT SUCCESSION
Colfax, Wash., 1913

4£ro- Festucal Pinus l 4&ro Festucal Pinus
£yro" || Conso. | Conso. I fly” | Conso. Conso-
Conso |ciation cies | Conso: ciation cies
Ciation Clatlon
Depth, 2 Inches Depth, ro Inches
May 7. . . . . . • * * * * * * * * 20.*C.| 8.7 || 15.0 | 13.o 6.0
June 6. . . . . . . . . . . . . . . 3I.O || 2 I.5 I2.5 || IQ.5 IS.O | I2.0
June 20. . . . . . . . . . . . . . 17.5 | 16.2 || I2.5 | 15.5% 15.0% I2.5* | 9 A. M.
June 20. . . . . . . . . . . . . . 22.5 I 7.5 | 12.5 || 20.0% | 16.5% | 12.5% 2 P. M.
June 20. . . . . . . . . . . . . . 21.5 17.5 | 13.o i 19.0% 17.0% 12.5% 6 P. M.
July 7. . . . . . . . . . . . . . . 29.0 19.5 I5.0 || 27.0% | 19.0% 14.5%
July 2I. . . . . . . . . . . . . . . 26.5 23.o I8.0 || 25.5% 22.0% 16.7% 9: I5 A. M.
July 2I. . . . . . . . . . . . . . . 28.0 22.5 I7.5 || 27.0% 24.0% 17.0% | 1:30 P. M.
July 2I. . . . . . . . . . . . . . 32.5 22.o 18.0 || 29.5% 25.0% 17.5% | 6 P. M.
July 30. . . . . . . . . . . . . . 35.o 22.o | I4.o 28.0% 20.0% 14.2%
August 13 . . . . . . . . . . . . 20.5% | 18.5% I5.0° 22.0 | 18.5 14.5
August 27 . . . . . . . . . . . 26.5 | 20.0 I5.0 || 22.5 | I 8.0 | I4.O
September Io. . . . . . . . . 22.5% 13.0% II.5* | 19.5 || 14.5 | 12.5
* Readings taken at a depth of 4 inches.
38 ''
Southeastern Washington and Adjacent Idaho.
39
Kamiak Mt., 1912
Festuca g Pseudo- Festuca * Pseudo-
e Pºntes f * Pizzes f sº
cºia. Consocies Ž. cºis. Consocies jº.
- Mictium . Mictium
Surface Depth, 12 Inches
May 3. . . . . . . . . . . . . . II.0° C. 7.5 6.o 8.0 7.0 S.O
May 12. . . . . . . . . . . . . . 27.5 I5.5 IO.5 I5.5 I3.O. 8.5
May 25. . . . . . . . . . . . . . II.5 II.O 9.5 I3.0 IO.5 7.5
June I. . . . . . . . . . . . . . 2I.5 I7.5 I4.O 3 I.5 I3.0 9.0
I913
Depth, 2 Inches Depth, 12 Inches
May 17 . . . . . . . . . . . . . Io.o° C. 7.5 5.2 9.5 7.0 5. O
May 24 . . . . . . . . . . . . . I6.5 I 2.2 9.5 I5.5 9.5 7.5
June 2 . . . . . . . . . . . . . . I8.5 I4.5 IO.2 I8.O II.7 IO.2
June 8 . . . . . . . . . . . . . . 24.5 I3.0 II. O I8.O II.5 IO.S
June 17. . . . . . . . . . . . . . 23.2 I2.5 8.5 I5.5 Io.7 8.5
June 26. . . . . . . . . . . . . . I4.2 II.5 9.5 12.5% IO.2% 9.5%
July 2. . . . . . . . . . . . . . . 9.7 II.5 9.2 Io.7% II.5% 8.7%
July 15. . . . . . . . . . . . . . I7.0 I 2.2 IO.2 I6.5% II.7% Io.5*
July 27. . . . . . . . . . . . . . 35.0 I7.5 I6.o 24.5 I4.5 I3.O
August 6. . . . . . . . . . . . . 22.0 tº tº gº tº I4.5 2.I.O tº & © tº II.5
August I5. . . . . . . . . . . . I9.7. I2.5 IO.5 17.5% 12.5% Io.5*
August 22. . . . . . . . . . . . 25.5% 16.5% I4.5* 22.5 I4. O I2.5
August 29. . . . . . . . . . . . 27.0% I6.0% I5.2% 23.0 I4.5 I3.O
September 5. . . . . . . . . . . 21.5% 13.2% II.2% I8.O I3.2 II.2
* Readings taken at a depth of 4 inches.
Viola, Idaho, 1913
Festuca Pºzzus *seudo- | Festuca Pºzzzz's Aseudo-
Conso- Conso- *suga- Conso- || Conso- tsuga-
ciation cies Zaria: ciation cies Zaria:
Mictium Mictium
Depth, 2 inches Depth, Io inches
May 3. . . . . . . . . . . . . . 9.5°C. 5.O I.5 6.5 4.5 I.5
May 24. . . . . . . . . . . . . I8.O IO.O IO. O. I3.5 8.5 7.5
June 18. . . . . . . . . . . . . I6.O I2. O II. O I5.O II.O 9.0
June 26 . . . . . . . . . . . . . 2I.O I2. O II. O I9.5* II.0% II.0%
July IO . . . . . . . . . . . . . 2.I.O. I3.0 I2. O 20.5% I2.5% II.7%
July 17 . . . . . . . . . . . . . 23.5 II.5 II.O 20.0% II.5% Io.5%
July 29 . . . . . . . . . . . . . I7.5 I2.5 I2. O I9.0 II.5 IO.5
August 8. . . . . . . . . . . . I8.5 I4.0 I3.0 2O.O I3.5 I3.0
August 20. . . . . . . . . . . 28.O I3.7 II.7 I9.0 I3.0 II.5
August 30 . . . . . . . . . . . 25.0% I6.0% I4.0% 2.I.O I5.0 I3.0
September 6. . . . . . . . . 24.0 I2.7 II.O I7.5 I3.0 II. O



* Readings taken at a depth of 4 inches.
39
4O
A Study of the Vegetation of
Cedar Mt., 1914
Pºzzes | Lazzar- Thuja. Pºzzus Larix- Thuja.
Conso- Abies Conso- Conso- Abies Conso-
cies Mictium ciation cies Mictium ciation
Depth, 2 inches Depth, ſo inches
July 3. . . . . . . . . . . . . . 21.0°C I4.5 I3.O I7.o IO.O IO.O.
July 18 . . . . . . . . . . . . . I8.5 I3.0 I2. O I6.0 II.o IO.5
July 25 . . . . . . . . . . . . . I9.5 I2. O II.O l . . . . . . . IO.5 9.5 .
August I. . . . . . . . . . . . I8.of 7.5i 6.5i 2.I.O I2.5 II.5

f Readings taken at a depth of 2 feet.
A discussion of light values as affecting succession had best be
given in connection with the study of the development of the
forest communities.
THE PRAIRIE-PLAINS FORMATION
The prairies represent an extreme westward extension of the
prairie-plains formation east of the Rocky Mountains.” This
great grass land area is here represented by the Agropyron-
Festuca association. It occupies a belt of varying width between
the desert Scrub formation on the west and the Pacific Coast forest
formation on the east. Thus three vegetational frontiers are seen
to meet within the region covered by the present investigation.
Altitudinally, it occupies an area whose westward boundary has
an elevation of 1,200–1,300 feet, while eastward it reaches an
altitude of about 3,500 feet. • - -
The prairies are limited on the east by that combination of
climatic and edaphic factors which make tree growth possible, a
type of vegetation with which the prairie can not favorably com-
pete. The changed climatic conditions are largely due to in-
creased altitude and are especially expressed in greater precipita-
tion. Likewise, coniferous tree growth is demarked more or less
1 At the present time, I am not quite clear whether we should properly
speak of the prairie-plains formation or whether, indeed, we have here two
grass land formations. In any case, the vegetation of the Agropyron-
Festuca association more nearly simulates that of the prairies proper,
Agropyron spicatum being an ecological equivalent of Andropogon sco-
parius east of the mountains.
4O
Southeastern Washington and Adjacent Idaho. 4. I
as
clearly by the edge of the great lava sheet. Exceptions to this are
seen especially along river canyons where xerophytic forest trees,
such as pines, may follow down the canyons, and extend out upon
the basaltic soils. Indeed, in the canyon of the Palouse River a
belt of such woodland extends clear across the prairie community
and drops out only at an altitude of 1,450 feet, and where it meets
the desert scrub formation. But because of the peculiar rigors
that forest frontiers meet, tree species invade the prairie with
extreme slowness, notwithstanding the fact that there may be
sufficient soil moisture in such situations for the maintenance of
a woodland cover.
On its lower and western border the prairie-plains. formation
gives way to the desert scrub formation. No sharp geographical
boundary can be drawn between the two formations. Under the
stress of low available soil water, the rainfall being here only I2
to 14 inches, soil depth plays a determining rôle. The prairies,
with the loss of their less xerophytic components, extend far
westward and to lower elevations upon deep soil. On the other
hand, the desert scrub formation, occupying the shallow soils of
the scab-lands and rim-rock, may extend far into the prairies.
Indeed, about Rock Lake and thence eastward along Pine Creek,
the scab-land sage is represented clear to the Idaho boundary.
Likewise, it occupies a zone in the warm Snake River Canyon,
extending through the prairie region. .
As would perhaps be anticipated from the nature of the transi-
tion zone occupied by the Agropyron-Festuca association, its com-
position in the drier portion is strikingly different from that of
the well developed upland part. The latter is characterized not
only by a greater number of important non-grassy species and a
denser plant cover as well as by the absence of certain character-
istic desert plants, but also by a change in habit of a dominant
grass, Agropyron spicatum (including var. inerme), which under
the less xerophytic conditions abandons its bunch habit in part
and becomes a sod former. Because of these differences the
formation may be separated into a more xerophytic part, the
Agropyron consociation, and a less xerophytic Festuca con-
sociation.
4 I
42 A Study of the Vegetation of
The Festuca Consociation
This consociation occupies the larger part of the area covered
by the prairie-plains formation. Along the thin soils of the
canyons the ecotone between this and the Agropyron consociation
is often very sharp, but westward and southward it shades im-
perceptibly into the latter. - -
The plants that share in the botanical composition of this con-
sociation in eastern Washington and adjacent Idaho are given
in the following lists of species which are classified into three
groups based upon their relative abundance and ecological im-
portance, - -
Composition of the Festuca Consociation
Dominant Species
Agropyron spicatum (includ- Festuca ovina ingrata
ing var. inerme)* Koeleria cristata
Balsamorhiza sagittata Poa sandbergii
Principal Species
Achillea millefolium lanulosa Leptotaenia multifida
Astragalus arrectus . Lupinus ornatus
Erythronium grandiflorum Potentilla blaschkeana
Geranium viscosissimum Rosa nutkana
Helianthella douglasii Sieversia ciliata
Hoorebekia racemosa Symphoricarpos racemosus
Hieracium scouleri
Secondary Species
Agoseris grandiflora Arnica fulgens
Agoseris heterophylla Aster fremonti
Allium acuminatum Aster laevis geyeri
Alsine nitens Astragalus spaldingii
Antennaria luguloides Bromus brigaeformis
Apocynum pumilum . Bromus hordeaceus
2 The nomenclature in this paper is that of the Flora of Southeastern
Washington and Adjacent Idaho, by C. V. Piper and R. Kent Beattie, 1914.
42
Southeastern Washington and Adjacent Idaho. 43
Calochortus macrocarpus
Carum gairdneri
Carea: geyeri
Castilleja lutescens
Circium foliosum
Circium palousense
Claytonia linearis
Clematis hirsutissima
dogswellia triternata
Collinsia tenella
Comandra pallida
Deschampsia calycina
Drymocallis convallaria
Elymus glaucus
Epilobium adenocaulon
Epilobium angustifolium
Epilobium paniculatum
Erigeron corymbosus
Fritillaria pudica
Galium boreale
Gaillardia aristata
Gentiana oregana
Gilia gracilis
Heuchera glabella
Hookera douglasii
Iris missouriensis
Linum lewisii -
Lithospermum ruderale
Lupinus leucophyllus
Lupinus wyethii
Mertensia oblongifolia
Olsynium grandiflorum
Orthocarpus tenuifolius
Pentstemon confertus
Phlow speciosa
Poa ampla
Senecio atriapiculatus
Sidalcea oregana
Silene douglasii multicaulis
Solidago missouriensis
Synthyris rubra
Trillium petiolatum
Vaccinium caespitosum
Valeriana edulis
Viola adunca
Wyethia amplexicaulis
Zygadenus venenosus
The prairies of eastern Washington, because of their grassy
verdure and sod-like appearance in spring and early summer, gave
rise to the term Palouse (Fr. pelouse, a land clothed with a short,
thick growth of herbage), a name applied by the Jesuit mis-
sionaries. However, as the dry summer season progresses the
prairies become quite brown and dry, except on the steeper north
hillsides and in the moist valleys. The south and southwest slopes
present a vegetational cover with a decidedly more xerophytic
stamp than the latter situations. Indeed, this is so pronounced
that rather careful and extensive investigations of the different
habitat conditions were made. Although a part of these results
43
44 A Study of the Vegetation of
have been published elsewhere (16, 17), it seems well worth while
considering them in a brief manner at this time.
Two stations were maintained in these prairies throughout the

P(A) || JUMA || || Jºr | Alſóws7 || SEP7.
u
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l
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55 | | J.' /
T
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if
/
M.
ſ / .
- - II/ / / I -
§4– - |\/ DS/ Y | \-ºl
N \ // / \ N
—PTN
15\- • * N. V -I
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2 /-
Yal N-- / f
{-12-tº- /
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& SR-4.
FIG. II. Evaporation rates on a southwest slope (solid lines) and a
northeast slope in the Festuca consociation during 1913 (heavy lines) and
1914. The dotted graph gives the evaporation rates on the southwest slope
and at a height of 50 centimeters during 1914.
44
Southeastern Washington and Adjacent Idaho. 45
growing seasons of I913–14. One was located on a southwest
slope about 65 feet from the crest of a hill somewhat less than the
average height, and another at an equal distance from the crest
of the same hill and on an average northeast slope. The average
daily evaporating power of the air at the two stations respectively
is shown in Fig II.
An inspection of these graphs shows a remarkable similarity in
the general course of either pair throughout the season. How-
ever, the difference in the amount of evaporation on north and
South slopes is just as striking. During 1913 the average daily
evaporation on the northeast slope was 16 c.c., which is only 64
per cent. of that on the southwest slope (25 c.c.). The season of
1914 was considerably drier and gave higher evaporation rates on
both slopes (23.9 c.c. on northeast, and 33 c. c. on southwest) with
a ratio on the two slopes of 72: IOO.
The evaporating power of the air on the southwest slope and at
a height of 50 cm. is also shown in the figure. It may be seen
that the evaporating power of the air at this height is increased
20 to 26 per cent. over that at 17 to 23 cm. This factor of in-
creased desiccation plays an important rôle in determining the
low stature of many of the prairie plants. Because of the cool
nights, about 8o per cent. of these high water losses occur during
the day. When we consider that the daily evaporation in July
and August often reaches 40 to 55 c.c., and at a time when the
available soil moisture is depleted to a depth of two feet, we can
see the necessity for extensive root-systems in the substratum
as well as aérial structures for enduring drought.
The greatest factor in causing the differences in evaporation on
the two slopes is the same one that has so profoundly influenced
the topography, namely, the wind. During the season of IQI3
(April 16 to September 3) the wind was from a southerly direc-
tion 68 per cent. of the time and a total of 13,605 miles passed
over the southwest slope at a height of 50 cm., while only 56 per
cent. as many miles were recorded by an anemometer similarly
placed on a northeast slope. In general, these conditions were
duplicated in the season of 1914 with the ratio of IOO: 49. Since
the factors of temperature, humidity, and wind movement are
45
46 A Study of the Vegetation of
quite satisfactorily summed up by measuring the evaporating
power of the air, the differences of temperature and humidity
shown in the two habitats need be discussed only briefly. Al-
though the plant community reacts directly upon temperature,
humidity, and wind, and these react upon each other, the response
of the plant is controlled by humidity.
The temperature of the air at a height of 8 cm. above the soil
surface as recorded by thermographs and checked by a large
number of thermometer readings shows a mean daily range vary-
ing from about 25° F. in April and May, to 38° F. in July and
August. The daily maximum air temperature is reached some-
what earlier on the north than on the south slope, and is from
2°–3° F. lower.
The steep hillsides are often in the shadow long before the
setting of the sun. For long periods during the winter months
the sun does not strike the steep north slopes, as is evidenced by
the presence of frost, which may soon be melted elsewhere.
A continuous record of humidity kept for more than two com-
plete growing seasons shows that the air is often 5–Io per cent.
drier on the exposed than on the sheltered slopes. It is not un-
common on dry slopes and during late afternoons for the humidity
to fall to I5–20 per cent., while during the night it may rise again
to 75 per cent. or even to 95 per cent.
These data on aérial physical factors show conclusively that
the plants on south slopes are subjected to much more severe
conditions as concerns water loss than those on sheltered hillsides.
Likewise the water supply of the former is usually less and this
supply is depleted much earlier in the growing season. Before
taking up the subject of soil moisture, however, other important
differences in the soil occupying the two slopes should be noted.
The wind has drifted much soil and humus materials from the
exposed south slopes and deposited it on the steeper north and
northeast leeward slopes. The difference in the mechanical com-
position of the first foot of prairie soils on the two slopes re-
spectively, is shown in Table II. -
The humus content of the soils of north hillsides is greater at
all depths to 5 feet, in some cases more than 12 per cent. greater,
46
Southeastern Washington and Adjacent Idaho. 47
than on the exposed slopes, as was shown by six sets of humus
determinations made for each foot of soil on the two slopes, re-
spectively. This combination of more clay and more humus on
the north and northeast slopes reflects itself especially in the
increased water holding capacity of the soil. An average of six
determinations gave a mean water holding capacity of 56 per
cent. (based on dry weight at 104°C.) for the first foot of soil
on north slopes, as compared with 48 per cent. On south slopes.
This margin of 8 per cent. is rather an important difference in
favor of the soils on the protected slopes, since the wilting coeffi-
cients of the two soils differ but little. These substratum differ-
NMAY JUNE JULY PAUGUsT || 5EPT.
FIG. 12. Graphs showing the march of soil water to a depth of Io
inches from April to September, 1913 (heavy lines), and from May to
August, 1914, on a northeast slope (solid lines), and a southwest slope,
respectively. - 47

48 A Study of the Vegetation of
ences are pointed out here since it will be shown later that cer-
tain plants are quite confined to moist north and northeast
hillsides.
Studies of the water content of these soils have been carried
on since the spring of 1912. It will be unnecessary to burden the
reader with all of the data and graphs obtained, and only enough
will be given to make plain the seasonal march of soil water. In
Fig. I2 are graphs giving the march of soil water from April 25
to September 25, 1913, on a typical northeast and southwest slope,
respectively. The ordinates represent percentages of soil mois-
ture in the first ten inches of soil. The rainfall between the in-
tervals of readings is also shown in inches, each ordinate repre-
senting or inch. The horizontal solid and broken lines show
the wilting coefficients of the soils on the northeast and southwest
slopes respectively. The greater amount of moisture on the
northeast slope (in some cases being twice that of the southwest
slope) may be noted at a glance, while the fact that the soil on
the exposed slope reached its wilting coefficient about July 15,
and more than five weeks before similar conditions obtained on
the sheltered slope is significant. Records for the fall of 1913
were discontinued when the rains of late September replenished
the parched soil. In 1914 these ten-inch soil moisture determina-
tions were made only at longer intervals and with the object of
determining the time at which the wilting coefficient was reached.
The water contents on the dates of these determinations are indi-
cated by the light lines, the solid line representing soil moisture
on the northeast slope. The rainfall for June, 1914, being ap-
proximately normal (and not I.6 in excess of the mean, as in
1913) the wilting coefficient of these soils was reached much
earlier than in the preceding year. An examination of these
determinations, together with the rainfall records at Pullman,
shows that at no time after June 8 and until September 14, was
there water available for plant growth in the first ten inches of
soil on the southwest slope. The autumn and winter rains
replenish the soil of the water lost during the long period of
drought and in the following spring it again shows a maximum
Water content.
48
Southeastern Washington and Adjacent Idaho. 49
It is apparent from these data that prairie plants must obtain
their water from greater depths than ten inches, at least during
the dry summers. In fact, some of these plants penetrate to a
depth of 12 or 13 feet, while most of them get the bulk of their
* * =
||8
FIG. 13. Graphs showing the march of soil water to a depth of 5 feet
on a southwest slope from April 18 to August 15, 1914; and the water con-
tent of the soil on December 13, 1913. The dotted lines indicate water
contents on a northeast slope.
water from the second to the sixth foot of soil (Figs. I5a, 15b,
and 15c). Consequently, a consideration of soil moisture at these
depths is imperative for a proper understanding of root environ-
ment. These deeper soil water determinations (many to a depth
of 8 feet) were taken at intervals from December, 1912, to
August, 1914. Fig. 13 (solid lines) shows the march of soil water
from early spring until late summer of 1914, on a southwest slope.
It is apparent that there was still a downward movement of water

49
5O A Study of the Vegetation of
at depths of 4 and 5 feet after April 18, but from June 3 to
August 15 the soil moisture was gradually depleted at all depths
to 5 feet. The heavy horizontal bars give the wilting coefficients
at the depths indicated. On July 6 no water was available in the
second foot of soil and only a small margin over the wilting co-
efficient was present at 3 feet. The broken line indicates that on
December 13 of the preceding winter the soil was drier at three,
four, and five feet respectively, than at any other time indicated.
The fall rains had not then penetrated beyond 2 feet. While ex-
cavating root-systems during the fall, winter, and spring, an ex-
cellent opportunity was offered to study the rates of penetration.
The water penetrated very slowly and at about equal rates on all
slopes. By October 18 only the surface layer of 8 inches was
wetted, and in late March the wet soil reached a depth of not more
than 4 feet. The dotted graphs in the figure indicate the soil
moisture on the northeast slope. -
Aside from the lower temperature and greater humidity of the
north slopes, the actual amount of moisture available to these
soils is important in explaining the observed differences in mois-
ture content. The wind drifts over to the sheltered slopes much
snow, which upon melting adds to the soil water. Two examples
will suffice. In February, 1914, exposed prairie slopes had a
blanket of snow from 5 to 8 inches deep, while on the sheltered
slopes at the same time drifts 48 to 52 inches were measured.
The second, while an extreme case, is illustrative. During Feb-
ruary and March, 1913, while only one foot of snow lay on the
south and southwest slopes, the protected northeast slopes were
covered with drifts of well-packed snow from IO to 13 feet deep.
In Fig. I4 is shown the march of soil water similar to that in
the preceding figure, but for soils of a northeast slope. Here
again, the downward movement of water at 3–5 feet after April
18 is apparent, as is also the gradual depletion of soil water at
all depths to 5 feet. Likewise, the broken graph indicates condi-
tions similar to those explained for the corresponding graph in
Fig. I4. On August 15 no soil water was available above the
two-foot level. If the graphs in this figure are compared with
the corresponding graphs in the preceding one it may be readily
5O
Southeastern Washington and Adjacent Idaho. 5 I
seen that a much higher water content was maintained in the
soils on the northeast slope.
18
Fig. 14. Graphs showing the march of soil water to a depth of 5 feet
on a northeast slope from April 18 to August 15, 1914, and the water con-
tent of the soil on December 6, 1913.
In order to further check these deep soil water conditions
samples were again taken in duplicate on the northwest and south
slopes of another prairie-covered hill. These findings, indicated
in Table VI, check very closely with the preceding, and the strik-
ing difference between soil water content on the two hillsides at
all depths is well shown. -
It may also be noted that at each determination the soil at any
depth was drier than at the same depth at the time of the preced-
ing determination. On the south slope, it is interesting to note
that without exception, the soil moisture increased with depth, and
that the same condition maintains in most cases for north-side soils.

5 I
52 A Study of the Vegetation of
Thus it may be seen that topography with soil texture is the great
middleman that distributes the soil moisture to fill the gigantic
earthen reservoir, which again is largely emptied during the fol-
lowing growing season. The common farm practice in the
Palouse Region of alternating season after season the growing
of wheat with summer fallow, is a method of storing the mois-
ture from one year for use in the growth of the next year’s crop.
TABLE VI
THE MARCH of Soil WATER on A Northwest AND SouTH SLOPE RESPEC-
TIVELY. I9I4
May 22 | July 6 August 15
o”— 6” N.W. . . . . . . . . . . . . . 23.4% I5.2 II.6
S. . . . . . . . . . . . . . . . . I2.5 II. I 6.7
6’—I2” N.W. . . . . . . . . . . . . . 25.7 I3.7 I2. I
S. . . . . . . . . . . . . . . . . I 7.9 II.4 IO.2
At 2' N.W... . . . . . . . . . . . . - 27.0 I8.9 II.8
S. . . . . . . . . . . . . . . . . I9.9 - I2.6 x IO.2
At 3’ N.W. . . . . . . . . . . . . . 30.2 23.7 I4.4
S. . . . . . . . . . . . . . . . . 20.2 I.3.2. - IO.6
At 4' N.W... . . . . . . . . . . . . ... 27.2 - 24.9 I8.O
S. . . . . . . . . . . . . . . . . 22.O I7.3 IO.5
At 5' N.W. . . . . . . • - - - - - - 24.3 2I.3 I9.5
S. . . . . . . . . . . . . . . . . 22.4 I9.6 I2.3
The differences in soil temperature on the two slopes and at
various depths may be briefly noted here. Table VII gives the
soil temperature at a depth of 3 inches on the two slopes respec-
tively, for three representative days in July, 1914. The higher
temperature prevailing on the south slope as well as the greater
range in temperature is very marked.
TABLE VII **.
Soil TEMPERATURE AT A DEPTH OF 3 INCHES
Station Minimum Time Maximum Time Range Day
- * - A. M. P. M.
N.E. slope . . . . . 63.5°F. 5 75.0 3 II.5 July 27
S.W. slope . . . . . 67.o 7 93.0 4. 26.0 July 27
N.E. slope . . . . . 59.0 5 7I.5 3 II.5 July 28
S.W. slope . . . . . 68.o 7 94.0 4. 26.O July 28
N.E. slope . . . . . 6I.O 5 73.5 3 I2.5 July 29
S.W. slope . . . . . 67.o 7 95.0 4 26.O July 29

52
Southeastern Washington and Adjacent Idaho. 53
A comparison of a large number of temperature readings at
one foot on the two slopes reveals the fact that at this depth the
soils on the south slopes are from 3° to 5° F. warmer in early
spring than those on the north slopes and that these differences
may increase by late summer to 7°–Io" F. In Table VIII the
soil temperature from I to 5 feet on the two slopes at the base
station is given. -
TABLE VIII
Soil TEMPERATURE AT I-5 FEET on APRIL 18 AND AUGUST 15, 1914, on A
NoRTHEAST AND Southwest SLOPE, RESPECTIVELY
April 18 August 15
Depth -
N.E. S.W. N.E. S.W.
I foot. . . . . . . . . . . . . . . . 45.7 °F. 50.3 65.o 73.0
2 feet. . . . . . . . . . . . . . . . 45. I 50.O 61.7 70.O
3 feet. . . . . . . . . . . . . . . . 45.0 48.2 58.0 66.2
4 feet. . . . . . . . . . . . . . . . 45. O 47.O 57.2 64.4
5 feet. . . . . . . . . . . . . . . e 45.0 46.4 54.5 62.6
The higher soil temperature prevailing on the south slopes
has much to do with the earlier seasonal activities of many
plants here than of those on north hillsides.
Summarizing briefly the habitat conditions in the prairie, we
find the north and northeast slopes less xerophytic than the south
and southwest slopes. This is due in part to actually greater
precipitation caused by blowing snow, and in part to soil texture,
which is more open, has more humus, and a greater water hold-
ing capacity. These factors are reflected in the greater amount
of soil water and in lower temperatures. Likewise, these slopes
are sheltered from the drying southwest winds, and from the
perpendicular rays of the sun. This is reflected in slightly lower
air temperature and greater humidity, and especially in the lower
evaporating power of the air.
These differences in habitat are reflected in the vegetational
cover in a number of ways. The resumption of growth in late
March or early April is often from Io to 17 days earlier on the
warmer exposed slopes. Likewise, the same species flower and
dry up correspondingly earlier than on the sheltered slopes. The
vegetational cover is less dense on the exposed slopes, often 16 to
53
54 A Study of the Vegetation of
30 per cent. of the ground appearing bare by mid-summer. Closer
investigation, however, reveals that much of this space was for-
merly occupied by prevernal and vernal plants which have by this
time become dry and brown. However, relict xerophytic mosses
and lichens indicate the more open nature of the ground cover.
A careful census of the plant population consisting of scores of
list quadrats reveals striking differences, not only in the number
of individuals, but also in the floristic distribution of species.
On an average it was found that south slopes are clothed with
about II5 individuals per square meter, while the north slopes,
with only about 3 per cent. of unoccupied soil space, showed
more than 200 individuals in the same unit area.
Perhaps the most pronounced difference is the smaller number
or total absence of more mesophytic plant-forms which thrive in
moist situations. Erythronium grandiflorum, Trillium petiola-
tum, Capnorea villosula, Vaccinium caespitosum, and Viola
adunca are examples of species characteristic of moist north hill-
sides. Numerous species, such as Sidalcea oregana, Circium
foliosum, Valeriana edulis, Gentiana oregana, and others seldom
occur on south slopes.
The blue bunch-grass, Festuca ovina ingrata, ranking in im-
portance with Agropyron spicatum, is the most characteristic
grass of the region (Fig. 48). The slightly pale-green plants are
densely tufted into bunches from I to 4 inches in diameter. The
low, bushy, setaceous leaf blades scarcely exceed a height of I2
inches. It is not unusual to find as many as IO to 13 of these
bunches in a single square meter. The bunch habit, an aspect
of prairie vegetation which is found more or less developed in
practically all prairie regions, and one which has succeeded in a
remarkable degree in withstanding xerophytic conditions, is most
pronounced on the drier slopes. In moist situations the clumps
are smaller, but I have never found Festuca producing rhizomes.
Like the other prairie grasses Festuca flowers by the middle of
June. Since its root-system draws the water supply from the
upper 18 inches of soil, its drying out in July and resumption of
growth upon the arrival of the autumn rains can easily be ac-
counted for.
54
Southeastern Washington and Adjacent Idaho. 55
The June grass, Poa sandbergii, one of the pioneers of herba-
ceous vegetation in the moss consocies, is also perhaps one of the
most important interstitial plants of the prairies. It grows in
small tufts usually only about O.5 to I.5 inches in diameter but
as many as 30 to 40 of these may occur in a single minor quadrat
between the bunches of Festuca and Agropyron. It is called
June grass because of its habit of flowering in May or early June
and remaining dormant until the advent of the fall rains. This
means of evading drought is necessitated by its very shallow
root-system, which seldom exceeds 8 inches. Its xerophytic
tendencies are shown by its less abundance in mesophytic situa-
tions.
The sod-forming habit of Agropyron spicatum in the prairies
of eastern Washington is in marked contrast to its well developed
bunch habit on the rim-rock or in the shallower and drier soils
westward. I have found the soil quite filled with rhizomes of
considerable length connecting smaller clumps of this grass.
It may well abandon this marked xerophytic character, for
its long roots extend into the fourth and fifth foot of soil, and
tap the earthen reservoir far below the root limits of competing
grass species.
Another common bunch-grass, which, with the three preceding,
completes the list of dominant grass species, is Koeleria cristata.
Like Poa, the bunches are often small, but numerous. It com-
pletes flowering in early July and remains dormant until revived
by the autumn rains. Its well developed but short root-system
gets water from the first I5 inches of soil only.
The entire absence of late blooming grasses, such as An-
dropogon, Sorghastrum, Bouteloua, and others of the prairie-
plains region, may be accounted for by the peculiar distribution
of the precipitation. .
A most characteristic plant of the prairies, and one which for
a time often outranks the grasses, is the prairie sunflower, Bal-
samorhiza sagittata (Fig. 42). Its abundance, size, and duration
all unite to make it a very important ecological species. It is not
unusual to find a dozen of these plants in an area of four square
meters. Only on the steeper northeast slopes and moist valleys
55
56 A Study of the Vegetation of
is it absent. A medium-sized mature plant occupies an area of
4-5 square feet; it may have as many as 50–80 of the large sagittate
leaves and a total transpiring surface of 30 square feet. From
the short, thick, multicipital stem (I have counted 39 individual
leafy shoots on a stem 9 inches in diameter) the new leaves appear
in April. By the first of May the plant is often in full bloom.
Then, with its large, yellow flowers, it is the most conspicuous ob-
ject of the vernal aspect, which lasts until about June 1. After this
Ft.
71-
FIG. I.5°. This and the two following figures (15° and 15°) are bisects
showing the root and stem relations of important prairie plants. These
figures were drawn from photographs and from data obtained by the
excavation and examination of 325 root-systems of these eighteen species.
H, Hieracium scouleri. K, Koeleria cristata. B, Balsamorhiza sagittata.
F, Festuca ovina ingrata. G, Geranium viscosissimum. P, Poa sandbergii.
Ho, Hoorebekia racemosa. Po, Potentilla blaschkeana.
the whole aérial part dries up, but the dead leaves are conspicuous
throughout the year. It has a strong, woody tap-root, sometimes
reaching a diameter of 4 inches, which may penetrate into the soil
for a distance of 8 feet. Not only is it deep-rooted, but the ex-
tensive and wide-spreading laterals lay hold upon a very large
area of soil.
In another place will be found a detailed report of a study of

56
Southeastern Washington and Adjacent Idaho. 57
the root-systems of many of the most important prairie plant
species and it is there pointed out that the response of many of
the plants to severe environmental conditions is met by well de-
veloped and extensive root-systems (17). Figs. I5a, I5b, and
I5c show in part the results of these investigations as regards
root type and depth of penetration.
Standing well above most other prairie vegetation and con-
spicuous not only for its size but also often for its great abun-
dance is Leptotaenia multifida. This large, much branched, un-
belliferous plant occurs quite commonly on both dry and moist
# T-
gº º —ſ
º º -
º - º .
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FIG. I59. S, Sieversia ciliata. W, Wyethia amplexicaulis. L. l, Lupinus
leucophyllus. L. o, Lupinus ornatus. P, Poa sandbergii. L., Leptotaenia
multifida. A, Agropyron spicatum. -
hillsides. It often characterizes rather large areas, but even if
occurring sparsely it is nevertheless very conspicuous and espe-
cially in June, when, after flowering, the leaves turn yellow be-
fore drying up. - - -
Erythronium grandiflorum constitutes a well-marked prevernal
aspect society on moist north hillsides from early April to the first
week in May. Even before the plants open their large golden






57
58 - A Study of the Vegetation of
yellow blossoms, their great numbers, often more than IOO indi-
viduals in a square meter, give a distinct tone in contrast to the
gray background of dead vegetation. -
Later on by the blossoming of Amelanchier, Crataegus, Prunus,
and Rosa especially, the developmental shrub community be-
comes very conspicuous. But the prairies become veritable
flower gardens during the month of June. Then the large red
º: -
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sl-
FIG. I.5°. Hu, Heuchera glabella. A, Astragalus arrectus. S, Sidalcea
oregana. H., Helianthella douglasii. Ag, Agropyron spicatum.
blossoms of Geranium and Rosa mingle with the yellow of Poten-
tilla, Gaillardia, Castilleja, and Helianthella. Senecio, Astragalus,
Arnica, and societies of Wyethia brighten the landscape with their
yellow blossoms, while the tall, widely spaced, sentinel-like plants
of Cirsium foliosum with their showy red flowers add pleasing
variety. -
Likewise the purple flowers of various lupines are conspicuous.
Lupinus wyethii is only locally abundant. It is especially no-
ticeable in the vernal aspect. It often covers areas of the driest
hillsides and the whole aérial part dries up early. Lupinus or-
natus is very cosmopolitan over the high prairies and is an im-
portant species. Lupinus sericeus is confined to the warmer







58
Southeastern Washington and Adjacent Idaho. 59
valleys southward and westward. Here its size and abundance
make it an important floral component. Lupinus leucophyllus
is the most mesophytic of the group and is found at home typ-
ically on moist north slopes or in the valleys.
In the lower ground considerable areas are given tone by the
white flowers of Galium. But with the increasing stress of
drought the aestival aspect passes, lingering only in moister situa-
tions. Then the leaden landscape of dry balsam-root, drying
grasses, and silvery-leaved lupines and hawkweed is relieved only
by the yellow and the blue of sparsely spaced goldenrods, asters,
and Hoorebekia. -
I have described very briefly the well developed prairie repre-
sented by the Festuca consociation. Westward and southward
as the altitude decreases and the rainfall is correspondingly less,
many important species either become fewer in individuals, or
are found only in the most mesophytic situations, or indeed dis-
appear entirely. Among these the following may be enumerated:
Astragalus arrectus. Leptotaenia multifida
Carew geyeri Lithospermum ruderale
Cirsium foliosum - Potentilla blaschkeana
Drymocallis convallaria Rosa nutkana
Gaillardia aristata Rosa pisodarpa
Galium boreale Sidalcea oregana
Geranium viscosissimum Sieversia ciliata
Helianthella douglasii Symphoricarpos racemosus
Heuchera glabella Trillium petiolatum
Hieracium scouleri Viola adunca
Hoorebekia racemosa Wyethia amplexicaulis
The Agropyron Consociation
This community in an early stage of development covers hun-
dreds of acres of the thin soil in the scab-lands. The characteris-
tic plant is Agropyron spicatum. Areas characterized by this
consociation are peculiar because of the growth form of the domi-
nant species as well as a number of the commoner interstitials
which show various degrees of the same bunch habit. Numerous
59
6O A Study of the Vegetation of
other plants are mat-formers, while a few are more or less
shrubby in character. -
The bunches of Agropyron are often 1–2 feet apart, perhaps
only 2–5 occurring in a square meter (Fig. 47). The individual
bunches or tufts are composed of from Ioo—35o or more stiff,
erect stems, reaching a height of 2–3 feet. Several generations
of dead stems are to be seen in these persistent bunches, the old
leaves and culms forming a tangle at the bushy base. Conse-
quently the landscape appears just as characteristic in late sum-
mer when this dominant is drying out as in the fall when it takes
on renewed growth, or in early spring when a host of inter-
stitials for a time cover the ground with a green carpet. Agro-
pyron is the one grass best adapted for such situations. Its well
developed roots penetrate the moist crevices in the underlying
basalt to a depth of 4 or 5 feet. -
Grasses like Festuca ovina ingrata and Koeleria cristata with
rather short root-systems find this an uncongenial habitat. How-
ever, a few grasses with very short root-systems and an early
blooming habit are very successful interstitials. Of these, Poa
sandbergii and the low annual, Festuca pacifica, are by far the
most important. Hundreds of individuals of the latter fre-
quently occur in a single square meter. Mats of Antennaria
dimorpha and dense growths of Plantago purshii are likewise
common between the scattered bunches of the dominant. These
interstitials, together with numerous others are quite as common
in the preceding Poa-Polygonum associes of which this, indeed,
except for the dominance of Agropyron, might be considered a
late developmental stage. However, the presence of the rabbit
brush, Chrysothamnus nauseosus, C. viscidiflorus, Tetradymia
canescens, Erigeron hispidissimus, and various lupines, espe-
cially in pockets of deeper soil, indicates the developmental trend
toward the more typical Agropyron community. -
In the deep soils of the hills bordering the scab-lands the Agro-
pyron consociation is better developed. (Fig. 20). The appear-
ance of Festuca ovina indicates more favorable life conditions.
Indeed, the latter sometimes assumes equal importance with
Agropyron on the more moist slopes. But the larger amount of
6O
Southeastern Washington and Adjacent Idaho.
6 I
unoccupied soil surface, from 30 to 40 per cent., and the appear-
ance of several new species of a decidedly xerophytic stamp gives
this consocies quite a different physiognomy from the well de-
veloped prairies eastward. The following lists indicate the
dominant, principal, and secondary species: -
Composition of the Agropyron Consociation
Dominant Species
Agropyron spicatum
Principal Species
Achillea millefolium var. lanu- Festuca ovina ingrata
losa
* Chrysothamnus nauseosus
---
Chrysothamnus nauseosus gra-
veolens
Chrysothamnus viscidiflorus
Festuca pacifica
Lupinus ornatus
Lupinus sericeus
Poa ampla
Poa sandbergii
Tetradymia canescens
Secondary Species
Agoseris heterophylla
Allium acuminatum
Alsine nitens -
Antennaria dimorpha
Artemisia rigida”
Astragalus collinus
Astragalus spaldingii
- Balsamorhiza sagittata
Elymus condensatus
Carew filifolia
Cirsium undulatum
Clarkia pulchella
Cogswellia triternata
Epilobium paniculatum
Erigeron corymbosus
Erigeron hispidissimus
Eriophyllum lanatum
Gilia pharnaceoides
Koeleria cristata
Lupinus wyethii
Madia exigua
Madia glomerata
Phloa longifolia
Plantago purshii
Potentilla biennis
- Stipa comata
The rabbit brush, although more common westward, is an abun-
dant and conspicuous component of the bunch-grass community.
3 Relict,
62 A Study of the Vegetation of
Its shrubby growth-form, numerous, erect, fascicled, and dense,
white-woolly branches and white-woolly leaves, combined with a
greater height-growth than most of its associates, make it a con-
spicuous plant in the landscape. The non-woolly variety, Chryso-
thamnus nauseosus graveolens, not less conspicuous, is also very
abundant. Both plants extend well up the warm valleys and
canyons but are practically absent from the high prairies eastward.
Tetradymia canescens, with a growth form similar to the pre-
ceding half-shrubs, likewise lends a decidedly xerophytic tone to
the dry scab-lands. It reaches its eastward extension in this
region. - -
A plant which forms a rather distinct consocies is Elymus
condensatus. On moist flood-plains this grass reaches a height
of 3–5 feet. In such situations the stout stems are densely
tufted and areas of many acres may be dominated by this species.
In deep soils on the dry hillsides it is not infrequent, but here it
usually occurs in more or less isolated clumps. -
In the eastward extension of the Agropyron community along
the rim-rock of the streams into higher altitudes, many of the
species being confined to the warmer valleys, drop out. In such
situations Balsamorhiza sagittata is often abundant between the
bunches of Agropyron.
In conclusion it may be said that the plants of this consocies
live typically not only in a climate of lower rainfall but also one in
which the period of drought, owing to the warmer climate with a
growing season several weeks earlier, is correspondingly increased
as compared with that of the well developed prairies of the
higher altitudes.
In the preceding pages I have treated the Festuca and Agro-
pyron communities as climax units of vegetation. Without ques-
tion, favorable changes of climatic conditions, such as a slight in-
crease in rainfall, would cause an extension of the Festuca com-
munity into the area now occupied by the Agropyron consocia-
tion. The latter in turn would extend its area downward and
westward into the desert scrub formation. Indeed, such move-
ments of plant populations are easily traced in the new areas of
rim-rock and scab-land where they are brought about as a result
62
Southeastern Washington and Adjacent Idaho. 63
of favorable modifications of the edaphic conditions such as an
increase in amount or an increase of the water holding capacity
of soils. - -
Likewise, on its high eastern border the Festuca consociation
contains a potential shrub community. Almost everywhere Sym-
phoricarpos, Rosa, and Spiraea are present but are held in check
by competing herbs and grasses. A local disturbance of the
habitat such as the building of a fence or the burrowing of squir-
rels modifies it favorably by increasing the water holding capacity
of the soil and swings the balance in favor of the shrubs. Once
established the shrubs may furnish a suitable nursery for seed-
lings of the yellow pine and thus the prairie may give way to
forest. These modifications of edaphic conditions foreshadow
those which would be caused by a favorable swing of climate,
while the reverse of these conditions would follow an unfavor-
able change. Indeed, the balance between prairie, shrub, and
forest is so nicely adjusted that even a few years of exceptionally
dry or unusually wet weather would be recorded in the movements
of the vegetation. -
The seral stages of the Agropyron-Festuca association will next
be considered, and in this place we shall discuss those of the
xerosere only. This will be followed by a brief treatment of the
desert scrub formation, after which the xerosere will be traced to
its culmination in the climax cedar forest. \º
(See outline of vegetational units, page 19.)
LICHEN-Moss CoMMUNITIES
Where the basaltic rock is exposed along the canyon walls and
in the scab-lands, as well as upon outcropping ledges of crystalline
rocks on buttes and mountains, a flora of lichens and mosses
abounds. During the dry summer months the rocks appear quite
bare and devoid of vegetation, but upon the advent of the autumn
rains, not only lichens and mosses, but also the June grass, which
closely follows the latter in point of succession, takes on renewed
growth. Then these situations, with their new verdure, become
quite inviting. Three associes are easily distinguishable, of which
that dominated by various crustose lichens is the pioneer.
63
64 A Study of the Vegetation of
Composition of the Rhizocarpon-Lecidea Associes
. Dominant Species
Rhizocarpon geographicum Lecidea lapicida
Principal Species -
Acarospora chlorophana Lecidea fuscocinerea
Blastenia ferruginea Rinodina oreina
Lecanora calcarea -
Rhigocarpon geographicum is by far the most abundant and
widely distributed species. It occupies the most exposed situa-
tions and forms a well defined consocies. The greenish-yellow
color of the rocks is due to its presence. The characteristic
checking of the dry thallus undoubtedly aids greatly in the ab-
sorption of water.
Lecidea lapicida often covers areas of several square inches ex-
clusively. Like Rhigocarpon it is of sufficient abundance and im-
portance to be ranked as an associes. On the quartzite rocks
Rinodina oreima often replaces Rhizocarpon, dominating large
areas with its orange-colored thallus. It is often accompanied
by the cinnamon-brown Lecidea fuscocinerea. Further investiga-
tion will probably show these to be dominants of a distinct as-
socies. -
Often large areas of vertical cliffs of basalt appear as if painted
lemon-color because of the presence of the crustose Acarospora
chlorophana. -
Crustose lichens not only exert an influence at the contact of
thallus and rock, but the corroding effect of carbon dioxide and
other secretions extends beyond the thallus margins during moist
weather. This permits slow extension of the thalli or furnishes
the starting place for new ones. Thus lichens corrode and de-
compose the rock and by mixing its particles with their own re-
mains give opportunity for the growth of other vegetation. Cen-
ters of crustose thalli break up and folious lichens get in. Espe-
cially on the more weathered rocks and in slightly less exposed
situations a number of foliose lichens replace crustose forms.
64
Southeastern Washington and Adjacent Idaho. 65
About the foliaceous species, water not only has a better chance
to collect and be absorbed but evaporation is also less rapid. In-
deed, it is probable that the change from crustose to foliose lichens
is as great a change of habitat as happens anywhere in the sere,
although too minute in extent to be impressive.
Gyrophora-Parmelia Associes
This community is in general less marked than the preceding
and is characterized by the following foliose forms:
Dermatocarpon miniatum Parmelia conspersa
Gyrophora phaca Parmelia pubescens
Lecanora rubina -
Gyrophora phaca may easily be found invading the areas of
the preceding crustose forms and because of its growth-form
actually causing them to disappear on account of decreased light.
Thus it comes to dominate areas of greater or lesser extent.
Parmelia conspersa takes possession of new areas in a similar
manner. Dermatocarpon miniatum is characteristically found in
situations where water seeps out of the rock ledges during a part
of the year.
As soon as soil and humus begin to accumulate in the crevices
and larger pores of the rock, the more xerophilous mosses begin
to appear. The pores in the basalt vary from those microscopic
in size to those several inches or even feet in diameter. On a
single rock one may come across an infinite variety of stages from
the dry exposed top of the rock with its crustose lichens to the
creviced or roughened lower portions where foliose forms are
mixed with mosses, grasses, and other flowering plants. .
Grimmia-Tortula Associes
The moss of most common occurrence on the..rocks and the one
which is able to live in the most xerophytic situations is the black
moss, Grimmia montana. This moss, with its minute rhizoids and
power of withstanding desiccation, quickly follows the lichen stage
and even precedes several species of the foliose lichens in point
65
66 A Study of the Vegetation of
of succession. Starting from the vantage ground of a crack or
crevice, the small tufts collect wind-blown soil and lichen remains
about them and building upon this substratum increase their
area. Well-worn rocks are frequently covered with the blac
mats of the Grimmia consocies. - - -
Less xerophytic but far more abundant is Tortula ruralis.
Growing in places less dry than those occupied by Grimmia, it
surrounds the base of rocky outcrops and occurs on thin stony
Soil where its soft cushiony mats may cover areas of many square
meters. While Tortula is very abundant on basaltic ledges it is
sometimes partly or wholly replaced, especially about quartzite
rocks, by species of Polytrichum, especially P. piliferum and P.
juniperinum. -
In other situations, and especially on canyon walls with north
and northeast exposure other mosses are abundant, often covering
large areas of sheer rock surface or growing luxuriantly over the
thin stony soil. The following lists include the most important
of these together with a number of lichens which usually occur
with the mosses. Some of these lichens are less xerophytic than
the foliaceous forms already mentioned. Indeed, they are the
most exacting members of the foliose lichen community.
Brachythecium albicans - Ceratodon purpureus
Brachythecium erythrorrhizon Encalypta ciliata
Camptothecium aeneum Grimmia apocarpa
Camptothecium lutescens Mnium affine
Cladonia pyxidata - Ochrolechia upsaliensis
Diploschistes scruposus Peltigera canina
Pou-Polygonum Associes
In the thin soil between the fragments of broken rock, an area
over which Tortula ruralis and other mosses for a time have
control, bunches of June grass and plants of Polygonum majus
and Plantago purshii begin to appear (Fig. 18). Changes of
light and root competition react unfavorably upon the mosses,
while shallow-rooted plants are well adapted to dominate just
66
Southeastern Washington and Adjacent Idaho. 67
such areas. The broken rock fragments not only aid in the
percolation of water and prevent run-off, but also tend to reduce
evaporation. - -
The xerophytic character of Poa sandbergii has been discussed.
Polygonum majus with its wiry stems and diminutive leaves
answers well ecologically for a grass. Likewise, the linear-leaved,
spiked, densely hairy Plantago may be so considered.
Polygonum majus must be a plant of very low water require-
ment for, in spite of its shallow roots, it blossoms and appears
to thrive throughout the summer and fall in these stony soils. It
is especially noticeable among the rocks when most other plants
are dried out, and its abundance makes it showy notwithstanding
its tiny flowers. I have counted more than 1,000 individual plants
from 2–8 inches high in a single square meter. In deeper soils
of talus slopes it becomes a bushy plant, sometimes more than a
foot in height. r
In the scab-lands especially, Plantago purshii characterizes
large areas with its leaden color. •
The following plant lists include those especially characteristic
of this community:
composition of the Pod-Polygonum Associes
Dominant Species (Consocies)
Plantago purshii Polygonum majus
Poa sandbergii - -
Principal Species
Antennaria dimorpha - Eriogonum heracleoides
Antennaria luguloides Epilobium paniculatum
Clarkia pulchella . . . Festuca pacifica
Cogswellia grayi Madia exigua
Cogswellia gormani - Madia glomerata
- Secondary Species
Agoseris heterophylla Allium acuminatum
Agoseris grandiflora Alsine nitens
- 67
. 68 A Study of the Vegetation of
Alyssum alyssoides Festuca megalura
Arabis sparsiflora - Platyspermum scapigerum .
Arabis holboellii Ranunculus glaberrimus
Athysanus pusillus . Sedum douglasii
Bromus brigaeformis - Selaginella wallacei
Cogswellia macrocarpa Tellima tenella
Draba verna - Tellima parviflora
Eriogonum niveum Thysanocarpus curvipes
Eriogonum compositum
A number of the above species form more or less well de-
veloped socies. Cogswellia gormani, one of the earliest of pre-
vernal plants, though inconspicuous as an individual, grows in
such great numbers on the thin soils as to become quite promi-
nent in early spring. When 500–800 of these plants occur in a
square meter, as is often the case, with perhaps a third of them
in blossom, they indeed make the landscape appear as if covered
with “salt-and-pepper.”
Cogswellia grayi is much more important than C. gormani. It
covers large areas of rim-rock almost to the exclusion of other
species. Its large umbels of yellow flowers make it very con-
spicuous. -
Moist places on the thin soils are dominated for a time in early
spring by great patches of Ranunculus glaberrimus, a small plant
but one with large and showy flowers.
The Poa-Polygonum associes gives way to the community
dominated by Agropyron. The chief cause for the transition is
the accumulation of soil and the presence of rock crevices of
sufficient depth and width to furnish soil and water for the deep-
rooted bunch-grass. The early stage of the Agropyron con-
sociation, already described, well illustrates this change. Often
however, in the rim-rock throughout the less arid region, the
transition is more abrupt. Belt transects only a few meters long
often show zones of vegetation dominated by the characteristic
species of the Poa-Polygnum, Agropyron, and Festuca com-
munities respectively. These zones extend in a parallel manner
along the upper edge of rocky outcrops. Below the transition
68
Southeastern Washington and Adjacent Idaho. 69
may be even more abrupt, a linear distance of one or two meters
giving the necessary differences in soil depth. Consequently the
zones are narrower, but no less distinct.
The uneven disintegration of canyon walls and scab-land and
rocky butte ledges and the differences they offer in slope and
exposure and in depth and moisture of soils furnish so many
habitat conditions that perhaps two-thirds of the total flora find
here more or less congenial homes. In the crevices of a lichen-
covered rock and separated only a few inches from the lowly
inhabitants of the former may thrive a shrubby member of a far
more advanced community. An analysis of the habitat shows
each is growing in its proper place, the crustose lichen on the bare
rock, the shrub in a small area of rich, well moistened soil.
Striking differences are offered by habitats on sheltered and
protected slopes. Near Pullman, during the summer of 1913,
a station was maintained on a south slope in the Agropyron
community and a second in a rather open growth of low shrubs on
the opposite slope about half-way between the rock ledge and the
flood-plain thicket. Not only was the evaporating power of the
air found to be twice as great in the former situation, but the soil
moisture was only about half as great throughout the growing
season. Temperature differences were also striking. The soil
between the bunches of Agropyron frequently gave noonday
temperatures of 90° to Ioo° F., as compared with 70° F. at the
opposite station.
These illustrations of diverse habitat conditions will make plain
the fact that in addition to the plants already mentioned as
belonging to the Agropyron or Poa-Polygonum communities,
many others occur. *
Characteristic shrubs and lianas found either as crevice plants
on rocky talus slopes or forming thickets about springy places
are enumerated in the following lists: the numerals indicate their
relative importance. In the drier regions the shrubs are notably
fewer.
Amelanchier florida 2 Berberis repens I
Amelanchier cusickii I Clematis ligusticifolia 2
69
7O A Study of the Vegetation of
Crataegus columbiana 2 Ribes cereum I
Opulaster pauciflorus 2 Ribes cognatum 2
Philadelphus lewisii I Rosa nutkana I
Prunus demissa I Rosa pisodarpa 2
Rhus glabra 2 - Sambucus glauca 2
Rhus towicodendron 2 Spiraea corymbosa 2
Ribes aureum 2 Symphoricarpos racemosus I
In springy places among the rocks, which are often surrounded
by thickets, the following herbs are especially plentiful: ,
Alsine media Hydrophyllum capitatum
Cerastium vulgatum - Mentha canadensis borealis
Claytonia parviflora. Mimulus langsdorfii
Equisetum arvense Saarifraga columbiana
Equisetum hyemale robustum Scutellaria angustifolia
Galium aparine Vagnera sessilifolia
Galium asperrimum - Veronica americana
Among the most typical crevice plants other than those previ-
ously enumerated may be mentioned two ferns, Cheilanthes gracil-
lima and Woodsia oregana. The former is especially character-
istic of stony outcrops on the buttes and mountains. Heuchera
glabella should also be mentioned here. -
Other species peculiar to thin soils of rocky ledges are:
Amsinckia intermedia Phacelia heterophylla
Arabis holboellii Sisymbrium altissimum
Crepis gracilis Thalesia uniflora
Gilia aggregata Valerianella macrocera
The kaleidoscopic character of scab-land vegetation may well
be anticipated by a glance at Fig. 39. -
In the thin soil surrounding lichen- or moss-covered basalt may
be found herbaceous plants characteristic of the Poa-Polygonum
community. Or these may alternate with the shrubby growth
of scab-land sage. In the crevices of the rocks may be seen
7o
Southeastern Washington and Adjacent Idaho. 7 I
dwarfed bunches of Agropyron which is better developed on the
talus slope below. This gives way in the deeper soils of the
depressions or on protected slopes to various lupines, species of
Poa, Balsamorhiza, Hieracium, Gaillardia, and other species. The
depressions, if alkaline, may be clothed with dense growths of
Distichlis spicata, Spartina gracilis, or Poa brachyglossa and these
surrounded by a more or less distinct zone of Elymus condensatus.
The vegetational differences often occur in areas so local as
to be seen at a single glance. Alternating with a talus slope of
lichen-covered basaltic blocks and only a few feet away, may be
seen other slopes which at a little distance appear well clothed
with herbaceous vegetation. Such are the interesting situations
offered by the rocky soils of canyons and scab-lands.
DESERT SCRUB FORMATION
In the region under investigation the above formation is repre-
sented only in the extreme western part. This formation oc-
cupies much of the Columbia Basin, extending eastward to an
altitude of about 1,200–1,300 feet, and on southerly slopes much
higher. Excepting such species as are confined to the moist
ground along perennial streams, the great majority of plants are
either shrubs or thick-rooted perennial herbs or short-lived
annuals. The most conspicuous and ecologically important plant
is Artemisia tridentata. Other dominant species are the rabbit
brush, Chrysothamnus nauseosus, C. viscidiflorus, the scab-land
sage, Artemisia rigidia, the antelope brush, locally known as the
black sage, Kungia tridentata, and, in alkaline situations, the
greasewood, Sarcobatus vermiculatus. -
The life conditions in this region are strikingly more severe
than in the region of the high prairies eastward. During the
summer of 1914, Mr. James G. Dickson, my one-time student,
made determinations of water content, evaporating power of the
air, and soil temperature for a period extending from July 5 to
August 15, at Moxee, Washington, in the heart of this formation.
He found that the average daily evaporation throughout the
period from standard atmometers was 5I c.c., while during several
days in August it reached 74 c.c. The soil moisture at 6 and 12
71
72 A Study of the Vegetation of
inches respectively, never exceeded 2.8 per cent, while that at a
depth of 2 and 3 feet was only slightly higher. Conversely, the
soil temperature at 3 inches ranged from 77° F. to over 112° F.
Even at 12 inches the temperature was usually above 78° F.
The Artemisia-Atriplex association is represented in this region
by the Artemisia consociation.
The Artemisia Consociation
This consociation, dominated by Artemisia rigida, is a very
characteristic type of vegetation over large areas of scab-lands.
The scab-lands, as elsewhere indicated, are areas of basalt, prob-
ably the flood-plains of former streams, in part, thinly covered
with soil. These extend as long tongues over the branching sys-
tem of river tributaries between the hilly divides. While many
of these flats in this region are dominated by communities of
Agropyron or Poa-Polygonum, still large areas are characterized
by the scab-land sage. This perennial, low, scrubby growth is
well adapted to the driest situations on the thin, rocky soil (Fig.
16). Many species typical of the above mentioned communities
occur associated with the sage, as might be expected in this zone
of transition. Plants characteristic of the desert scrub forma-
tion occurring with the sage are Chrysothamnus nauseosus in-
cluding the variety graveolens, C. viscidiflorus, and Tetradymia
canescens. It has already been pointed out that some of these
play an important rôle in the Agropyron consociation.
In the Snake River Canyon beautiful examples of the abrupt
transition from the sage to the Agropyron community are abun-
dant. Rocky, exposed slopes reveal the former, while sheltered
slopes only a few meters distant show a well developed Agro-
pyron community. -
In passing from the prairie into the scab-land the change in
animal population is no less striking than that of the vegetation.
In the drier region the Townsend squirrel, Citellus townsendi,
replaces the larger Columbian squirrel, C. columbianus, so plenti-
ful eastward. Likewise the presence of the burrowing owl and
rattlesnake is characteristic.
72
Southeastern Washington and Adjacent Idaho. 73
The Sarcobatus Consocies
Communities of the greasewood, Sarcobatus vermiculatus,
occur in alkaline soils of the flood plains or depressions in the
scab-lands. This scrubby growth, with its pale branches and
fleshy leaves, stands out in distinct contrast to surrounding vege-
tation. The consocies is represented only locally and careful
study of it was not made.
THE PACIFIC COAST FOREST FORMATION
The coniferous woodland occurs in the eastern part of the re-
gion and chiefly in Idaho. While the forests in the main grow
on the soils produced by the weathering of old crystalline rocks,
it is not uncommon in certain parts of the region to find under-
lying rocks of basalt. Likewise, the sheltered slopes of isolated
quartzite buttes may be clothed with trees, or woodland may ex-
tend as tongues along the deeper canyons far into the prairie.
There exists a close relation between the development of the
physiography of a region and the life history of its forest com-
munities. This is nowhere better shown than in semi-arid cli-
mates where a slight change in elevation may so modify the pre-
cipitation and other life conditions as to turn the balance slightly
or wholly in favor of a tree form of vegetation. -
A study of the chemical composition of the soils of basaltic
origin as compared with those originating from quartzite, granite,
and other crystallic rocks, shows that they are not greatly dissimi-
lar (Table III). I am convinced that it is not the chemical com-
position of the soils of this region but rather their physical char-
acters that determine the type of vegetation which they support.
Of course the controlling factor of the physical composition
is, in this region of dry summers, their ability to hold water, pro-
vided always that sufficient humus is present to furnish the neces-
sary nitrates. Not only do these forest soils have a higher water
holding capacity than those of the basaltic prairies, as has already
been shown, but this property increases, due to increased humus
content, proportionally as the succession advances toward the
climax stage. That coniferous forests will grow upon the basaltic
soils is evidenced by their presence over considerable areas in the
73
74 A Study of the Vegetation of
upper Palouse Valley, but the best example is to be found in the
woodland growth of that high upfold of basalt in southeastern
Washington known as the Blue Mountains. Under the present
climatic conditions, the prairies appear to be a subclimax forma-
tion. .
The higher elevation of these forest-clad foothills and moun-
tains is sufficient to considerably increase the precipitation. The
prevailing southwest winds sweeping across the many miles of
open prairie and desert of northern Oregon and south central
Washington, but gradually ascending, here lose much of their mois-
ture. It is not unusual to observe on a morning in autumn or
late spring the surrounding mountains covered with snow while
no moisture has fallen upon the lower hills. Sometimes even iso-
lated buttes only 700–1,000 feet higher than the lava plateau are
snow clad and stand out in bold relief in contrast to the surround-
ing country. sº r
A rain gauge of the government pattern placed with Mr. J. B.
Kissinger 4 miles northeast of Viola, Idaho, showed, during the
years 1912—1914, an annual increase over the rainfall at Pullman
during the same period of 3 and 4.5 inches respectively. A simi-
lar gauge placed with Mr. Stratton on Cedar Mountain and at
an elevation of about 4,000 feet gave 4 inches greater precipita-
tion during the months of July and August, IQI4, than was re-
corded at the base station. Not infrequently, I have witnessed
rather heavy summer showers in the mountains while no rain fell
upon the plateau I,500 feet below. & . -
Not only does the change in altitude affect the amount of pre-
cipitation, but it also shortens the growing season. Snow lies on
the ground until late in May or indeed on the more protected
slopes even until June. Thus the season of drought is consider-
ably shortened. Likewise, the cool nights lessen the evaporating
power of the air. . -
The forests of the region make up a part of the Pacific Coast
forest formation. This formation is represented by the Thuja-
Tsuga association. A single consociation, dominated by Thuja
plicata, forms the climax community. Tsuga heterophylla, an
74
Southeastern Washington and Adjacent Idaho. 75
important member of the climax communities elsewhere, is not
represented in the area under consideration.
Symphoricarpos-Opulaster Associes
A shrub community usually occupies the transition zone be-
tween prairie and forest or at least is intimately associated with
the earlier stages of development of the latter. I have already
mentioned that on the most mesophytic hillsides a more or less
well developed scrubby mictium may compete with the grasses.
These shrubs are even better developed on the protected slopes
of the canyons, where, seepage from the rocks may form a very
congenial habitat, and where, indeed, they often entirely replace
the prairie. }Likewise, the sheltered sides of the lower buttes
and the more exposed slopes of those of greater elvation may be
covered with a rather dense chaparrall The presence of such a .
shrubby growth indicates increased soil moisture. This at first
may be due to slight unevenness in the topography such as a ridge
over which snow may be blown and accumulate in sufficient
quantity to furnish considerable additional moisture, or, it may be
due to biotic factors such as the loosening of the soil by squirrels
and other burrowing animals. The water holding capacity of
such worked-over areas is considerably increased and results in
an immediate dominance of various shrubs, especially roses, Sym-
phoricarpos or Spiraea, which show a much poorer development
in the drier, compact soils. The shrubs once present tend to
make conditions more mesophytic, a phase which constitutes their
most important rôle in succession. Not only do their fallen
leaves but also their decaying roots and rhizomes add considerable
humus to the soil, while their shade lowers the rate of evapora-
tion from the soil and at the same time prevents the too rapid
oxidation of the decaying organic matter. Such enriched soil
forms an excellent seed bed for species of xerophytic trees which
may invade the sodded prairies only with difficulty. Thus in the
normal succession the shrubs may prepare the way for tree
growth. The trees in their turn, because of their shade, espe-
cially if they are in dense stands, cause the shrubs to disappear.
The Symphoricarpos-Rosa Mictium.—The members of this
75
76 - A Study of the Vegetation of
community although present generally throughout the less xero-
phytic portion of the prairie region seldom come into dominance
except on moist sheltered slopes or ravines. In such situations,
dense tangles of shrubby growth consisting of the following
species may occur: . -
Rosa nutkana Spiraea corymbosa
Rosa gymnocarpa Vaccinium caespitosum
Symphoricarpos racemosus Prunus demissa
Here, as along sheltered canyon slopes, they may dominate local
areas almost to the exclusion of grasses and herbaceous plants.
They are frequently accompanied, especially in the latter situa-
tions, by dwarfed specimens of Crataegus brevispina, Amelan-
chier spp., or Populus tremuloides. Where pines occur the pre-
ceding trees and shrubs are invariably accompanied by Opulaster
pauciflorus, the latter usually becoming the dominant shrub.
The roses are especially conspicuous in May, when their large
showy blossoms fill the air with a delicate perfume. Spiraea is
always less conspicuous, while Symphoricarpos is much more
noticeable in the fall when it is covered with its large white fruits,
than throughout its flowering period. Vaccinium caespitosum
often covers large areas and while its reddish leaves may add tone
to the vernal aspect, later, because of its low stature, it is more or
less hidden by other vegetation.
Opulaster Consocies.—As already indicated Opulaster pauci-
florus is the shrub par excellence of the scrub community. It
often covers large areas in almost pure growth especially in the
deeper canyons and on the outlying buttes. Its well developed rhi-
zones enable it to invade the grass land which soon gives way be-
cause of the dense shade, if the shrubs are well developed. In
most situations, the balance between chaparral and prairie is so
nicely adjusted that for a long time the shrubs occupy places in
swales, ravines, or other irregularities of the surface, while
tongues of grass land extend down on the slightly higher eleva-
tions (Fig. 23). Among the last herbaceous plants to give way
are those of the more mesophytic type such as Geranium, Dry-
76
Southeastern Washington and Adjacent Idaho. 77
-
mocallis, and Sidalcea, but not infrequently Opulaster grows in
such situations as to replace the more xerophytic grasses and
Balsamorhiza.
Chaparral that is so dense as to almost exclude other vegetation
is characterized in early spring and before the leaves appear by a
layer society of Erythronium grandiflorum. These lilies are
often so numerous as to give the appearance of a yellow carpet
under the shrubs. In less shaded areas Ranunculus glaberrimus
and Olsynium grandiflorum are plentiful. The Opulaster con-
socies is very conspicuous in May, when its countless white blos-
soms give a distinct tone to the landscape. Likewise, in late
August and September the reddish-tinted drying leaves form a
pleasing variety to the monotonous brown of dry vegetation.
While Opulaster frequently characterizes considerable areas
alone, it is not infrequently associated with the buckbrush,
Ceanothus sanguineus. Indeed, the latter shrub may sometimes
become so abundant as to make up half of the mictium. The
buckbrush because of its oily seeds, is a very important and fat-
tening food for sheep on the summer range. Numerous other
shrubs, such as Holodiscus discolor, Prunus emarginata, and
species of Ribes are less important components of this consocies.
Prunus Consocies.—Local areas on the buttes are often charac-
terized by growths of Prunus emarginata. These vary from a
rather open growth of stunted shrubs only three feet high to
dense copses in which the cherry takes on the stature of a small
tree. The characteristic occurrence of this community in dry
open places is of considerable ecological significance. I have not
infrequently found invading pines extending their territory from
sheltered slopes into the drier areas under cover of these shrubs.
Frequently the pines may be overtopping the cherries and indeed
beginning to replace them, yet a count of annual rings usually
shows that the latter were the pioneer woody plants.
Ceanothus Consocies.—On the exposed slopes of Cedar Moun-
tain and adjacent buttes, but seldom found elsewhere in the re-
gion, the sticky laurel, Ceanothus velutinus, often dominates.
This evergreen, semi-procumbent shrub, while seldom reaching a
height of over 4–6 feet, has numerous long branches which spread
77
78 - A Study of the Vegetation of
in all directions so that a single plant may cover an area of sev-
eral square meters. It is frequently so abundant as to form a
dense tangle very difficult to penetrate. Other common shrubs
associating with it are Ceanothus sanguineus, Pachistima myr-
sinitis, Salia scouleriana, Holodiscus discolor, and Spiraea corym-
bosa. On these steep, gravelly slopes the rôle of the shrubs in
catching surface washed materials including coniferous seeds
which are frequently buried under the debris, and in shading the
soil against excessive evaporation, is an important one in the
establishment of the tree stage in succession. Of the forest trees,
Pinus ponderosa and Pseudotsuga mucronata are most likely
to be found in such situations.
The Pinus-Pseudotsuga Associes
Although much of the forest in this region has been cut over
and still larger areas swept by forest fires, yet large tracts repre-
senting all the consocies and mictia of the region are still found
in their primeval condition. This is due to the rough topography
which makes them inaccessible to the lumberman, while certain
areas have been set aside by the federal government as mineral
lands. - .
The above associes represents types of forest which occupy the
drier mountain slopes and are the transition stage from the grass
land and shrub to the more mesophytic forest communities.
Here are included the yellow pine and the Douglas fir consocies
and a pine-fir mictium. The former is the earliest in point of
succession and will be considered first.
Pinus Consocies.—Of all the forest trees of the region the
yellow pine is best fitted for the pioneer work of foresting prairie,
chaparral, or rocky areas. It overcomes xerophytic conditions in
part by striking its root-system deeply and spreading it widely,
thus laying hold upon large areas of soil. Rooted in rock crev-
ices it may make a height growth of only a fraction of an inch a
year and at the age of 40 or 50 years be only a few feet high, yet
such examples bear witness to its wonderful powers of resisting
adverse conditions. - . .
The difficulties of pines in invading grasslands should be recog-
78
Southeastern Washington and Adjacent Idaho. 79
nized. Many of the seeds which are overlooked by rodent popu-
lations never germinate. Of those that do germinate many dry
out before they have become well established. Other seeds are
prevented from reaching the soil because of the sod. However,
under a combination of favorable conditions a few seedlings be-
come fairly established. Surface wash may lodge the seeds
against a rock or bush or other obstacle and at the same time
cover them with soil. Opportune showers may so favor their
growth that they become well established. Having gained a per-
manent foothold they may reach maturity. These pioneer trees
establish a more congenial habitat for their offspring. The fallen
needles and branches catch more surface water and debris, and
decaying, aid the grasses in increasing the humus content and
consequent water holding capacity of the soil. Likewise, shading
prevents the rapid oxidation oft humus and at the same time
lowers the evaporating power of the air. It is not unusual to
find parent trees in prairie openings establishing about themselves
just such areas of ecesis. In this way forests may replace
prairies. *
The invasion of pines into chaparral is accomplished with less
difficulty, especially if the latter is of not too dense a growth.
The shrubs not only modify the edaphic condition in a manner
already indicated but also the aërial plant parts are greatly shel-
tered, especially from drying winds. I have noted scores of situa-
tions where shrubs were advancing up butte slopes into the prairie,
while numerous pine trees of all sizes and ages had established
themselves in the chaparral. However, the chaparral is often
so dense as to prevent the establishment of the pines. This
happens when the light under the shrubs falls to an intensity of
O.I.5. But usually, even in such situations, there are open places
in which forest growth may occur provided tree seeds are present.
It is probable in this semi-arid region that during the more
-favorable years of a climatic cycle the forest trees are able to
gain a foothold in situations where growth conditions would be
too severe ordinarily. An investigation along this line would
probably throw considerable light upon the puzzling problem of
an isolated stretch of yellow pine in the canyon of Union Flat
79
8O A Study of the Vegetation of
Creek, at a distance of I2 miles from any contiguous body of
timber. However, this is a phase of the problem which I found
little time to study. -
The yellow pine consocies forms the transition zone from
prairie or shrub to other types of woodland. In the mountains
it occupies exposed south or southwest slopes or only the tops of
these if the lower slopes are sheltered. Not infrequently it is
accompanied by Douglas fir. . -
On the exposed buttes only scattered trees may occur among
the shrubs on north slopes. In other cases well developed for-
ests may be found. On higher buttes, the rocky tops, ravines,
and sheltered bases may be clothed with a pine forest, while large
stumps, or isolated pines towering above the Douglas fir and tam-
arack now in possession of the moist, sheltered slopes, tell the
story of a former occupation by a pine forest. Thus all stages
of development are strikingly shown on these butte ramparts of
the forest frontiers. Often on wind-swept ridges a sheltering
spur permits the growth of pines, while a slight descent from a
pine-clad ridge may reveal an entire change in tree dominants,
the Douglas fir and tamarack replacing the pine.
As already indicated, the pines have worked their way down
the Palouse River and along Rock Lake. In the shallow canyons
they are practically confined to the sheltered canyon sides. Doug-
las fir and Larix accompany them in the deeper canyons of the
Palouse River, but I have found only the former with the pine
about Rock Lake. Opulaster pauciflorus invariably accompanies
these forest outposts and its distribution is undoubtedly due to
chipmunks and squirrels, which are likewise ever present in pine
woods. Numerous plants, which otherwise are found only in the
mountains also occur in these pine-clad canyons. Among others
Aconitum columbianum, Actaea spicata arguta, Thermopsis mon-
tana, and Veratrum viride may be mentioned. In fact, the study
of plant populations upon wooded buttes isolated by a distance.
of from only a few to several miles from the forests proper is
fascinating and instructive, but one into which we can not well
enter here. *
The xerophytic conditions under which the pines grow about
8O
Southeastern Washington and Adjacent Idaho. 81
Rock Lake are remarkable. Upon the thin soils which seem able
to support only a Poa-Polygonum community and where even the
bunch-grass seems dwarfed, pine seedlings establish themselves,
rooting in the crevices, and eke out an existence for years. On
the rocks in early August, everything is dry and burned. Even
Amelanchier, cherry, and Spiraea become defoliated, still the
pines hold on until relieved by the advent of autumn showers.
Their stunted condition stands in marked contrast to their well
developed companions in the more protected places with deeper
soil.
In the open park-like growth of the yellow pine in the moun-
tains it is not unusual to find fine clean-boled trees 2.5–3 feet in
diameter towering above one or two younger generations. In
other situations the forest is less open, and is then usually mixed
with Douglas fir. In such situations, as one would expect in a
transition region from prairie to forest, the ground cover is com-
posed more largely of prairie than of forest forms. The follow-
ing lists indicate the more important shrubs and herbs of open
pine woods: ->
Amelanchier florida Rosa gymnocarpa
Arctostaphylos uva-ursi Rosa nutkana
Ceanothus sanguineus Salix scouleriana
Holodiscus discolor Spiraea corymbosa
Opulaster pauciflorus Symphoricarpos racemosus
Pachistima myrsinites Vaccinium macrophyllum
Prunus emarginata
Achillea millefolium lanulosa Aster conspicuus
Agropyron spicatum (including Astragalus mortoni
var. inerme) * Bromus marginatus
Anemone piperi Calamagrostis rubescens
Antennarid dimorpha Campanula rotundifolia
Antennaria luguloides Deschampsia elongata
Antennaria racemosa Deschampsia calycina
Apocynum pumilum Drymocallis convallaria
Arnica cordifolia Epilobium angustifolium
8 I
82 A Study of the Vegetation of
Erythronium grandiflorum Leptotaenia multifida
Fragaria bracteata Lupinus laviflorus
Fragaria platypetala : Lupinus ornatus
Frasera fastigiata Moehringia macrophylla
Galium spp. Pentstemon pinetorum
Geranium viscosissimum Potentilla blaschkeana
Helianthella douglasii Pteridium aquilinum pubescens
Hieracium albiflorum Sedum douglasii &
Juncoides campestre
As the pine forest becomes more closed the shrubs tend to dis-
appear, and usually considerable Douglas fir and tamarack are to
be found. The transition from pine to the pine-Douglas mictium
or Douglas-Larix mictium takes place in this manner. Not only
has the closed pine forest established more congenial conditions
for tree seedlings, but it has made its own reproduction difficult
if not impossible by a cutting down of the light intensity. In
order for yellow pine to thrive, the sun must strike the seedling
the greater part of the day. Small openings in forests made by
the removal of a few trees by windfall or natural death do not
furnish sufficient light. However, the slightly more tolerant
Douglas fir and tamarack can not only grow here, but actually
shade out competing pine species. Thus the physiognomy of the
forest may gradually change from pine to Douglas fir or to Doug-
las fir and tamarack with all intermediate combinations in mic-
tium. Consequently, mixed forests of pine and Douglas fir into
which Larix is invading are common. The shrubby and herbace-
ous flora, of course, is intermediate between that already given
and that of the more mesophytic Pseudotsuga–Larix mictium to
be described. -
The Pseudotsuga Consocies.—Well developed communities of
Douglas fir occupy the upper exposed slopes in the mountains.
Frequently the stand is 90 per cent, or more pure Douglas fir but
lower down the slopes it is almost invariably mixed with Larix
and white fir, to which, along the ravines, it may almost entirely
give way. Likewise, in more open places it is accompanied by
yellow pine.
. 82
Southeastern Washington and Adjacent Idaho. 83
Where the growth is rather pure, the trees, a foot or more in
diameter, are pruned high and the dense shade permits of a very
sparse ground cover. In such situations, the light intensity may
fall to O.OI or even lower. Except for a few specimens of Coptis
occidentale, Anemone piperi, Moehringia macrophylla, Thalictrum
occidentalis, or Vaccinium macrophyllum the ground may be
quite bare. Douglas fir grows only poorly at light values of O.O25.
Such forests may completely surround bare rock-topped moun-
tain peaks, but more often give way to shrubs or small areas of
grass land. Except in such situations I have never seen Douglas
fir invading prairie.
Douglas fir is far more common in mixture with Larix and
white fir than in forests of which it is the dominant. The per-
centage of Douglas fir is usually determined by the slope and ex-
posure and consequent soil moisture. While Laria and white fir
do not grow in as dry soil as Douglas fir, the latter is less domi-
nant in moister situations because of its greater light requirements:
Larix is slightly, and white fir much more tolerant than Douglas
fir. -
The Laria-Abies Associes -
This associes makes up by far the most important forests of
the region. Great stretches of moist mountain slopes are covered
with forests of which either Larix or Abies are dominant or more
often the two form a mictium. The Larix consocies, dominated
by Larix occidentalis, occupies the higher slopes of lower water
content intergrading from the Douglas fir above to the more meso-
phytic white fir-cedar mixture of the moister slopes, ravines, and
valleys. • -
It has already been pointed out that the larch is only slightly
less xerophytic than the Douglas fir. Its place in the succession
is intermediate between the Douglas fir and the white fir. Its
ability to withstand the wind-storms that uproot white pine and
white fir is an index of a well developed root system, and this
probably accounts for its ability to grow in soils where the surface
layers are quite dry. -
The absence of Larix seedlings in a mature forest shows that
83
84 - A Study of the Vegetation of
the young trees can not endure shade. However, openings of
greater or lesser extent constantly occur in primeval forests due to
the dropping out of old trees, to windfalls or to fires. Since
Larix seedlings can do well in openings where the sunlight enters
during the middle of the day, the chances for reproduction are
always present. The tamarack, because of its thick bark, is dis-
tinctly a fire-resistant tree, often remaining unscathed where
white pine and white fir are killed. Hence, large tracts of burned
areas, where the tamarack was abundant, now appear to form
nearly pure Larix communities. However, an examination of the
new tree populations, together with comparisons with unburned
contiguous areas, reveals the true mixed nature of the original
forest. In such places the white fir is especially prominent.
Abies grandis is not only more tolerant of shade but is also more
mesophytic than the larch. I have not infrequently found fir
seedlings in shade so dense as to exclude all other trees except
the cedar. White fir seedlings can grow in light as low as O.O2
to O.ors. Under such conditions, however, growth is poor. While
it can develop in open places in rather dry soil, it is more exacting
in soil moisture requirements than either Douglas fir or Larix.
The position of Abies in the normal succession is beautifully
illustrated on sheltered slopes of outlying mountain spurs and
buttes. Passing from the dry open pine forest one can find all
stages from pine-Douglas fir mixture dominated first by the pine,
to a pine-fir-tamarack mictium where the tall, spindly, bushy-
topped pines, many of which are dead, tell the story of the lost
struggle for light. Areas of higher water content on the same
slope may show Pseudotsuga–Larix mixtures with the fir losing its
dominance and Abies grandis appearing. The next stage is that
of a Laria-Abies mictium with the coming in of cedar. Charac-
teristic plants of these drier Larix-Abies forests are given in the
following lists: - * -
_*
Ceanothus sanguineus - Ribes viscosissimum
Holodiscus discolor Rosa gymnocarpa
Opulaster pauciflorus Rubus parviflorus
Pachistima myrsinites Salia scouleriana
84
Southeastern Washington and Adjacent Idaho. 85
Vaccinium macrophyllum Fragaria platypetala
Anemone piperi Linnaea borealis longiflora
Arnica cordifolia Micromeria chamissonis
Calamagrostis rubescens Pyrola picta
Chimaphila umbellata Thalictrum occidentale
Coptis occidentalis Trillium ovatum
Cytherea bulbosa Vagnera amplexicaulis
Fragaria bracteata
While Opulaster pauciflorus is the most abundant undershrub
in the pine consocies, in the Larix-Abies community it remains
only as a relict. It is not unusual to find areas of dead nine-
bark under a growth of tamarack or white fir.
Ribes viscosissimum while occurring sparingly in the earlier
stages of succession is frequent in these dry fir-tamarack forests
but is a more typical undershrub of the more mesophytic fir-
tamarack community. In the cedar consociation it gives way to
the more mesophytic Ribes lacustre.
Likewise, Arstostaphylos uva-ursi, common in pine woods, is
seldom found here. Linnaea borealis longiflora replaces it, cover-
ing large areas with a carpet of trailing stems. The twin-flower
is less abundant in the deep shade of well developed fir-tamarack
forests and drops out completely in the cedars.
In well developed forests the white fir not infrequently reaches
a diameter of 2.5–3.5 feet, while neighboring tamarack trees reach
diameters of similar proportions. Likewise, Douglas fir fre-
quently attains a diameter of 3 feet, a relatively small tree com-
pared with the dimensions it reaches in the humid Washington
region west of the Cascades. Under the closed canopy of such a
forest, shrubs are almost excluded and herbaceous plants are not
abundant. The light values may drop to an intensity of only O.OI
or even O.OO7.
In more open places a poorly developed shrubby layer may
overtop an upper layer of herbaceous plants, which like the former
is not well developed. Indeed, both may be absent and then a
scattered growth of low-growing herbs with a few fungi and
mosses may partially cover the ground. The sparse growth of
85
86 A Study of the Vegetation of
fungi as well as such saprophytes as Corallorhiza spp. and Ptero-
spora andromedea appears meager indeed to one accustomed to
the rich fungal flora of an eastern deciduous forest.
The following lists indicate the shrubs, herbs, and some fungi
commonly found in well developed mesophytic forests:
Chimaphila umbellata
Lonicera utahensis
Menziesia ferruginea
Pachistima myrsinites
Pyrus sitchensis
Ribes viscosissimum
Actaea spicata arguta
Adenocaulon bicolor
Anemone piperi
Arnica cordifolia
Asarum caudatum
Clintonia uniflora
Coptis occidentalis
Disporum majus
Fragaria spp.
Galium spp.
Boletus sp.
Clavaria spp.
Coprinus comatus
Gyromitra esculenta
Ribes lacustre
Rosa pisodarpa
Rubus parviflorus
Sambucus melanocarpa
Vaccinium macrophyllum
Linnaea borealis longiflora
Mitella stauropetala
Osmorhiza divaricata
Pyrola spp.
Streptopus majus.
Thalictrum occidentale
Tiarella unifoliata
Trillium ovatum
Vagnera amplexicaulis
Morchella bispora
Morchella spp.
Peziza spp.
Sarcosoma globosum
These changes in the shrubby and herbaceous populations from
the less mesophytic to the more mesophytic members as the suc-
cession advances are no less characteristic than the changes in the
lichen flora which abounds on the trees. While in open pine
woodland the trees are often covered with the yellowish and gray-
ish patches of Letharia vulpina and Parmelia physodes, in the
early stages of the Douglas fir-tamarack community these lichens
give way especially to species of Alectoria. Of these the long
pendant thallus of A. fremonti is especially characteristic, while
86
Southeastern Washington and Adjacent Idaho. 87
A. oregana is less abundant. As conditions become more meso-
phytic in the Laria-Abies community, Usnea dasypoga begins to
predominate, while in the climax cedar consociation the trees are
often beautifully draped with the long yellow strands of this
species. Under such conditions species of Alectoria are not fre-
quent.
Other trees which are more or less important components of
these forests are the white pine, Pinus monticola, lodgepole pine,
Pinus murrayana, yew, Tarus brevifolia, and Engelmann spruce,
Picea engelmanni.
The white pine, although more abundant and of greater value
on the bottom lands of streams in northern Idaho than anywhere
throughout its range, is not an important tree in the area under
consideration. It occurs only sparingly throughout and where it
is best developed on the moister slopes, seldom makes up more
than 5 per cent. of the forest and reaches this abundance in only
local areas. It appears to require a moister soil than white fir, but
its seedlings can stand considerable shading. Perhaps the drye
ness of the climate combined with the ravages of forest fires
which may kill it and leave larch and red fir uninjured, combined
to make it an unsuccessful tree in this region.
The lodgepole pine, Pinus murrayana, occurs very sparingly
throughout the western forest frontier of the region. Eastward
and northward, especially in cut-over and burned-over regions, it
assumes considerable importance, occurring in mixture through-
out all types of forest, and frequently forming dense even stands
over considerable areas. Unlike the yellow pine it seldom plays
the rôle of pioneering in grass land and since it is distinctly a “fire
tree” of a weedy nature, it had best be considered in another
place.
Taarus brevifolia is very rare in this region, occurring only oc-
casionally along ravines and then taking on only a scrubby form.
Its rôle in the forests of the region is insignificant.
Engelmann spruce, so characteristic of high mountain slopes
elsewhere, while never found in great abundance, is rather a fre-
quent forest tree at the highest altitudes, especially in wet ravines
and about the edges of alder swamps. It does best in soils where
87
88 - A Study of the Vegetation of
the deeper strata are very moist. Outside of meso-hydrophytic
situations it does not flourish in the region and even here it does
not reach the usual size of the species. It sometimes forms a
very broken and fragmentary zone between the alder-willow com-
munity and the climax cedar forest. Its ability to tolerate shade
to a greater degree than Douglas fir or tamarack probably ac-
counts for the presence of its seedlings in drier situations, for I
have shown that conditions under typical stands of white fir and
tamarack are, as regards the seedling stage, fairly mesophytic.
Likewise, its power to germinate in the open, providing there is
sufficient soil moisture, accounts for its presence, often in dense
stands, in situations where drifts of melting snow keep the soil
well moistened in otherwise apparently rather dry, rocky situ-
ations. Like other shade-enduring species, it makes a more rapid
growth in these situations than in the shade.
The Thuja Consociation
The climax forest community of the region and the one in the
xerosere with the lowest light intensity, greatest soil and air
humidity as well as lowest temperature, is that dominated by the
cedar, Thuja plicata. The best protected and most mesophytic
mountain slopes as well as the well watered ravines are clothed
with a growth of this cedar. These often form 90 per cent. or
more pure stands and the trees may reach diameters of 3–5 feet.
In such well developed forests, the light intensity ranges from
o.OI5 to o,005 and even to O.Oo3, and except for the seedlings of
the cedar the ground may be quite bare. But usually the forest
canopy is sufficiently open to permit a growth of a few shade-
enduring shrubs and numerous herbs. Of these the following are
typical of the consociation: -
Ribes lacustre - Rubus parviflorus
Aconitum columbianum Circaea pacifica
Anemone piperi - Claytonia asarifolia
Asarum caudatum Clintonia uniflora
Athyrium cyclosorum Coptis occidentalis
88
Southeastern Washington and Adjacent Idaho. 89
Galium sp. Viola glabella .
Streptopus majus. Viola orbiculata
Tiarella unifoliata Vagnera amplexicaulis
Trillium ovatum
The high humus content and consequent great water holding
capacity of the soil is probably due in part to the lack of forest
fires. For it is easy to see how the more moist areas in the deep
ravines would be less subject to burning than the drier slopes
with their proportionally greater amount of undershrubs. The
forest floor supports the best developed fungus flora of the region.
This includes species previously enumerated. However, even
here the fungus flora is relatively scanty. -
Because of the shade the trees are often pruned high, while the
branches are draped with long strands of Usnea. Often at higher
altitudes Picea engelmanni accompanies the cedar down the moist
ravines but never assumes very great importance.
The greater mesophytism and tolerance of the white fir as con-
trasted with that of the tamarack and Douglas fir are shown by the
presence of the former in the mixed cedar-white fir forest. It is
the last of these trees to give way to the cedar, certain communi-
ties showing gigantic relict white firs while all of the saplings are
those of the cedar. Proceeding up the slope from a cedar com-
munity the white firs become dominant as the cedars become
smaller and less frequent on the drier soil, then a zone of white
fir and tamarack is passed, while further up in this mixture
Douglas fir becomes more abundant. Of course, the illustration
is rather overdrawn for the accidents of windfalls, and especially
fires, may often greatly alter these conditions.
The formation as a living developing entity has reached its
maturity in the cedar consociation. Because of the low light
intensity the establishment of the seedlings of the other forest
trees of the region in the cedar community is impossible. Hence,
the adult stage will go on indefinitely repeating itself generation
after generation, unless disturbed by some outside factor as a
forest fire or the hand of man. -
Having traced the normal development of the forest through the
89
90 * A Study of the Vegetation of
xerosere to its climax community, we will next consider briefly
a hydrophytic adsere, after which we will take up the secondary
*
succession or subsere.
The Adsere. Alnus-Salix Associes
Distinctly hydrophytic plant communities characterized by
Alnus sinuata, Salia scouleriana, and Pyrus sitchensis occupy
broad wet ravines and springy places often high up on the moun-
tain sides. The weight of the great banks of snow which drift
over the trees and sometimes almost bury them, pushes them into
a semi-procumbent position leaning down the slope. The alder,
which is usually dominant, reaches a diameter of 2–5 inches and
a vertical height of only 12 or 15 feet, while not infrequently it
attains a length greater than twice its height. Likewise, the
willow and mountain ash and also the mountain maple, Acer
glabrum douglasii, which accompany it in this habitat, are
bent down the slopes by the weight of the snow. Because of
the late melting of the snow in such situations and the resulting
springy nature of the soil, coniferous tree seedlings are excluded.
Engelmann spruce, as already indicated, often borders such alder
thickets and in turn gives way to the cedar.
In this tangle of semi-prostrate trees, shrubs are nearly ex-
cluded, although Sambucus melanocarpa and Ribes lacustre occur
rather infrequently. A dense herbaceous undergrowth which
almost completely conceals the ground is made up of the follow-
ing mesophytic species:
Aconitum columbianum Disporum oreganum
Actea spicata arguta Mertensia membranacea
Athyrium cyclosorum Osmorhiga divaricata
Circaea pacifica Senecio triangularis
Claytonia asarifolia Streptopus amplexifolius
Clintonia uniflora Thalictrum occidentale
Disporum mafus . Trillium ovatum
The preceding plant species together with certain other meso-
phytic shrubs and herbs and hydrophytic mosses border the moun-
90
Southeastern Washington and Adjacent Idaho. 9 I
tain streams, which, indeed, may be fringed with a more or less
fragmentary alder community.
SUBSERE. REFORESTATION OF CUT-OVER AREAS AND
BURNS
Since the direction of development is always forward and
toward the climax community of a region, the removal of the
plant cover, such as a forest, makes possible the repetition of
the story of normal succession. This, however, may be consider-
ably modified and the amount of repetition determined by the
degree of completeness of the destruction.
In studying the natural reforestation of the region, it will be
advantageous to consider first the secondary succession or sub-
sere after cutting, and afterwards the reëstablishment of forests
following burns.
Naturally many of the outlying pine-covered areas were early
cleared by the settlers and the land used for the cultivation of
crops. Where small tracts have been allowed to “go back” after
removing the yellow pine and burning the brush, the first years
show a rapid growth of shrubs while the intervening spaces are
dominated largely by prairie species. Opulaster pauciflorus,
Spiraea corymbosa and other shrubs, which in the denser stands
have been suppressed by the shade, spring rapidly into dominance,
while Epilobium angustifolium, Cirsium palousense, Pteridium
aquilinum pubescens, and Deschampsia spp. mingle with various
prairie species already designated as occurring in yellow pine
forests. Among these, yellow pine seedlings grow vigorously
and the forest, finally reëstablishes itself. Of course, repeated
fires kill the pine seedlings, burn off the shrubs, and favor the
invasion of prairie plants. Although prairie fires in the Palouse
Region were never so severe as those of the Great Plains, it is
probable that they played an important rôle in preventing the in-
vasion of conifers into the grass land.
In most of the more accessible canyons of the mountains,
lumbering has been carried on and in some places the operation
of the lumberman has been followed by ground fires. In prac-
tically all cases, except in the lodgepole region eastward, where
9I
92 A Study of the Vegetation of
reforestation has occurred, the new forest has usually about the
same composition as the old. In these cases, the composition
of the previous forest was determined, of course, by a study
of the stumps, by checking with the adjacent forest, especially
primeval forest areas on similar adjacent slopes. The following
case, found by repeated trials to be rather typical, is illustrative.
Belt transects through a second growth forest occupying an
area in Thatuna Hills cut over about twenty-five years ago gave
the following percentage composition: -
Moist North Slope Dry South Slope
Yellow pine . . . . . . . . O.5 per cent. Yellow pine ........ 36.0 per cent.
Douglas fir . . . . . . . . 4.0 per cent. Douglas fir . . . . . . . . I4.0 per cent.
Tamarack ... . . . . . . . 30.0 per cent. Tamarack ... . . . . . . . . IO.0 per cent.
White fir . . . . . . . . . . 26.0 per cent. White fir . . . . . . . . . . 40.0 per cent.
Cedar . . . . . . . . . . . . . . 39.5 per cent.
Superficially such moist slopes appear to be clothed with nearly
a pure tamarack forest, due to the more rapid height-growth of
this species. In such young forests the cedars are often small,
in fact, many are mere seedlings. A count of the annual rings
shows that they came in after the other trees had, by their shade,
made conditions less xerophytic. Their importance in the general
composition of the forest might be overestimated from their high
percentage. Farther up the slopes they are scattering, and only
near the moist base are they present in great abundance. Like-
wise, the white fir on the south slope occurs mostly in dense
thickets near the base. On the open south slope trees averaged
only I per square meter, while on the north slope the average was
3.5 per unit area. -
No less characteristic of the two types of forests are the shrubs
and herbs of the undergrowth. Opulaster pauciflorus, Ceanothus
velutinus, and Salix scouleriana make up the chief shrubby growth
on the south slope, often covering many square meters exclusively.
On the north slope both Opulaster pauciflorus and Ceanothus
velutinus occur but rarely, while Vaccinium macrophyllum is
more abundant than Salia scouleriana. Coptis occidentalis,
Clintonia uniflora, Thalictrum occidentale, Mitella stauropetala,
92
Southeastern Washington and Adjacent Idaho. 93
Galium sp., Asarum caudatum, Anemone piperi, Pyrola bracteata,
Cytherea bulbosa, and species of Vagnera, all found here, are
typical plants of the moister slopes, and contrast markedly with
Calamagrostis rubescens, Bromus marginatus, Pteridium aqui-
linum pubescens, Pentstemon pinetorum, Astragalus mortoni, Aster
conspicuus, Anaphalis margaritacea occidentalis, Antennaria
racemosa, Pedicularis racemosa, and Berberis repens, found on
the more open south mountain side.
Cut-over areas in the northeast part of the region, where as
a result of fires lodgepole pine is frequently abundant, showed in
addition to the usual herbaceous and shrubby growth and tree
seedlings of all the common tree species, a frequent dominance of
Pinus murrayana. The numerical dominance is a result of its
prolific seeding habit, brush fires being sufficient to open many
of the cones, while its rapid height-growth makes it stand out
prominently when mixed with other species. The developmental
history of such areas will be considered under reforestation of
burns.
A report of the study of the natural reforestation of burned
areas in the mountains of northern Idaho has already been made
(6). Although much of the area there included lies outside of
the boundaries of the present investigation, still conditions are so
similar that a brief statement may be included here.
During the month of August, 1910, the greater part of northern
Idaho and much of eastern Montana was swept by one of the
most extensive and destructive forest fires ever experienced in
that part of the country. In many heavily wooded canyons the
draft was so violent during the fire and the heat so intense as to
destroy every vestige of life above ground.
The town of St. Maries, Idaho, lies against the slopes of foot-
hills, which, prior to 1910, were covered with a more or less mixed
forest of coniferous trees comprising the following species: Pseu-
dotsuga mucronata, in practically all situations; Pinus ponderosa,
abundant on south slopes and in exposed and rocky situations;
Larix occidentalis associated with Abies grandis and Pseudo-
tsuga; Pinus monticola and Thuja plicata accompanied by indi-
93
94 A Study of the Vegetation of
viduals of Pseudotsuga and Abies, confined generally to the
canyons and rich levels at the bases of north slopes. .
These mountain slopes were overrun by fire on August 21 and
22, 1910. As they seemed to represent fairly the average forest
conditions for northern Idaho, it was decided that here would be
a most satisfactory place to carry on a study of the problem of
natural reforestation.
Among the first pioneers to reclaim the unshaded and charred
soil were Funaria hygrometrica and Marchantia polymorpha.
Cirsium palousense, Erigeron acris, and Epilobium angustifolium
were the chief herbs, whose wind-blown fruits afforded them an
early entrance. Likewise, the numerous seedlings of Salix
scouleriana may be accounted for in the same manner, while
numerous others sprang up from the underground parts of the
older willows characteristic of more open areas. The presence of
Opulaster pauciflorus, Arnica cordifolia, and Erythronium grandi-
florum may likewise be accounted for by the fact that the fire
left unharmed the rootstocks of the shrub and of Arnica and the
corms of the lily. - -
In the spring of 1911 and the second year after the fire, Epi-
lobium angustifolium was predominant everywhere. The indi-
viduals varied from mere seedlings to plants 12–18 inches in
height, often as many as 30 to 50 individuals occurring in a single
square meter. Thousands of the smallest were succumbing to an
epidemic of Aecidium. Next in importance to the fireweed was
the thistle, Circium palousense, which with Antennaria luguloides
and the species enumerated as occurring the preceding year,
formed a considerable herbaceous carpet over the burned area.
Every inch of the ground otherwise unoccupied seemed covered
with Funaria hygrometrica. The following shrubs, Opulaster
pauciflorus, Rosa gymnocarpa, and Rubus parviflorus, which were
more or less abundant, had, like several of the herbs in the fol-
lowing list, been able to survive the fire by means of underground
propagative parts. The bulbs of Zygadenus venenosus and Fritil-
laria lanceolata, and the corms of Erythronium grandiflorum, all
of which were present in considerable abundance, were found at
depths of 5–7 inches below the surface of the soil. Other plants
94
Southeastern Washington and Adjacent Idaho. 95
present in greater or lesser abundance were Potentilla sp., Mitella
stauropetala (abundant), Leptotaenia multifida, Disporum majus,
Moehringia macrophylla, Coptis occidentalis, Viola spp., two
species of Lathyrus, and Vicia sp.:
It is of interest here to note that in spite of the terrific heat
which must have prevailed over those mountain slopes, except
where the undergrowth was dense, a considerable depth of humus
remained intact. Where this was wholly consumed and the soil
had been washed bare by rains there was a fairly complete turf
of Funaria and Marchantia along with certain herbaceous plants
already given. The effects of this forest fire were more pro-
found in certain parts of the forest than in ‘others, depending
Somewhat upon the topography of the devastated region. In the
“draws” or small lateral canyons where growth conditions were
such as to produce the most excellent stand of white pine, Douglas
fir, white fir, and cedar, the fire was most destructive, leaving no
trees alive. Whereas, on lateral or secondary ridges it was fre-
quently observed that from 25 to 75 per cent of these species, in-
cluding yellow pine, survived the heat. These constituted the
seed trees so valuable in the reforestation now going forward.
A diligent search was made for any seedlings of the cone-
bearing trees characteristic of the region under observation, and
a few were found. A limited number of these (all were Laria.
occidentalis) were from seed germinated in 1911, but the majority
were but a few weeks old at the time of observation. They were
indeed scarce—not more than 60–80 per acre on north and east
slopes and none at all on south and southeast or southwest ex-
posures. In two instances it was observed that as many as 15–2O
seedlings were growing in one spot as though a cone had become
planted and all its viable seeds had germinated. The area in-
vestigated seemed to show no signs of any other conifer, which
fact corroborates observations of a similar nature made in cer-
tain denuded sections of Thatuna Hills. However, by the fall
of the same year, many seedlings of Thuja, Larix, Pseudotsuga,
and a few of Abies had sprung into existence. -
It is probable that some of these seeds were furnished by
scattered surviving parent trees in the vicinity, although it is
95
96 A Study of the Vegetation of
equally certain that others buried in the moister duff escaped burn-
ing. Hoffman (7) has shown that seeds of Thuja plicata may
remain dormant in the soil for two years, while those of Pinus
monticola and Pseudotsuga mucronata may be buried in the duff
for six years and still remain viable.
The distribution of the seedlings was very irregular. In some
areas of a square meter or more none could be found, while in
other more favored spots the seedlings would average as many
as 8 per square meter. The ground occupied by these seedlings
was well covered with a mulch of the dead leaves and stems of
such herbaceous plants as have already been described for the
region.
On the denuded south slopes where the original forest growth
consisted of an abundant stand of Pinus ponderosa with scattered
individuals of Pseudotsuga mucronata, notwithstanding the pres-
ence of a growth of Symphoricarpos, Pteridium, Epilobium,
Cirsium, Achillea, and other plants in considerable abundance
and so intermingled as to form a semi-shaded protected area, no
coniferous seedlings were present. Their absence was no doubt
due to insufficient soil moisture and excessive evaporation.
These south mountain sides and their ravines and canyons will
in the course of time be reclaimed by a new growth of yellow pine
and Douglas fir unless ground fires occur and natural growth
conditions are obliterated. -
Reforestation studies in areas swept by fires of all degrees of
severity were made, especially in Thatuna Hills. In some cases
only very local areas were concerned, while in others the fires
covered considerable territory (Fig. 43). In practically all cases
sufficient seed trees were either left standing in the burned area
or on unburned ridges in close proximity to furnish the seed for
reforestation. - -
About twenty-nine years ago, many square miles of these hills
were overrun by a fire which destroyed more or less completely
much of the virgin timber, leaving here and there a few living
trees representing the different species to serve as seed trees in
subsequent years. These burns covered chiefly the north and
northeast slopes of the mountains. In these mixed forests of
96
Southeastern Washington and Adjacent Idaho. 97
white fir, tamarack, Douglas fir, and cedar, the thick-barked
tamarack suffered least, and often only the trees of this species
less than 6–8 inches in diameter were killed. This gave rise to
what are apparently nearly pure forests of tamarack; but in most
cases sufficient seed trees of the other species were left to in-
sure re-seeding, and at present a new generation of white fir and
tamarack are especially prominent. -
Notwithstanding the now open nature of the forest, the ground
being covered with the blackened and charred remains of fallen
white firs and cedars, many of the smaller tamaracks, though
dead, are still standing. The larger ones, often fire scarred, but
living, are not usually more than 12–14 inches in diameter. They
reach a height of 85—IOO feet, and, like the fir, reveal by their
high pruning a former forest with a closed canopy.
On the upper and middle slopes the ground is more or less com-
pletely covered by a thin layer of raw humus, consisting mostly
of the leaves of the tamarack. Numerous quadrats in various
areas revealed a predominance of the seedlings of the white fir,
often 20–25 per square meter, while Douglas fir and tamarack
were less abundant. In many places the mineral soil was destitute
of vegetation, while only a sparse growth represented by Hier-
acium albiflorum, Clintonia uniflora, Adenocaulon bicolor, Galium
sp., Chimaphila umbellata, Micromeria chamissonis, Pyrola picta,
and a few other scattered species occurred elsewhere.
The severe conditions under which the tree seedlings were
growing were shown by the fact that even the oldest, which came
in at least three or four years after the fire, did not exceed a
height of I5–18 inches. - • * * ,
Judging from adjoining and unburned forests of a similar com-
position it appears that the remaining tamaracks by a spreading
of their crowns had considerably increased the shade, the light
value often falling to o.2, and thus offering considerable protec-
tion to the tree seedlings. - •
Farther down on similar slopes, where the fire left fewer trees
standing, both because fewer tamarack trees were present and
because the fire was more severe, quite a different stage in repro-
duction is to be seen. Here, because of more moisture and the: '
97
98 A Study of the Vegetation of
open light, average major quadrats revealed as many as 200 tree
seedlings. Of these nearly four-fifths were white fir and tam-
arack, about equally distributed, while the rest were Douglas fir,
white and yellow pine. Many of these were 19–20 years old, with
a height-growth of 6–13 feet, the tamarack as usual in the lead.
In the moist ravines young cedars were abundant. The early his-
tory of this forest was probably the same as that of the St. Maries
region already described.
In heavy burns in other parts of the region where big cedar,
spruce, white fir, and tamarack timber have been completely de-
stroyed, various species of shrubs, especially Vaccinium macro-
phyllum, Menziesia ferruginea, Salix scouleriana, and thickets of
Alnus, Rubus parviflorus, Ribes lacustre, Rubus macropetalus,
and maple had sprung up and almost completely covered with
their dense growth the fire blackened tangle of fallen trees. How-
ever, they form a good protection for the tolerant cedar and
spruce, and while they may shade out other seedlings for a time,
still there are always openings, and especially in drier soil where
the less tolerant but also the less exacting fir and larch can get a
foothold. -
Without further details the general story of reforestation of
burns in the region is as folows: Soon after the fire the ground
is more or less completely covered with cryptogamic vegetation of
which Funaria hygrometrica and Marchantia polymorpha are
dominant. Soon plants with wind-blown fruits appear. Of these
the following are most important: -
Epilobium spicatum Hieracium albiflorus
Salia scouleriana Antennaria luguloides
Cirsium palousense Anaphalis margaritaceae occi-
Erigeron acris - dentalis
Certain grasses, as Bromus marginatus, and fire grass, Agrostis
hyemalis, may predominate for a time but later give way to other
herbaceous growths, especially of Epilobium (Fig. 44). After
one or more years, varying with the severity of the burn and
degree of exposure, tree seedlings begin to become established.
Southeastern Washington and Adjacent Idaho. 99
These may be shaded by too dense thickets of various shrubs,
which may spring up from underground parts, and largely re-
place the herbaceous vegetation. But usually the shrubs form a
protection against wind and excessive evaporation. The trees in
turn suppress the shrubs and the mature forest, usually similar
to the one preceding, is replaced. -
Studies of reforestation in burns of varying severity show
more or less incompletely the several stages of the subsere. How-
ever, continued investigation in these and in completely burned
areas indicates the following seral stages, some of which may be
telescoped or even lacking in any one particular burned area.
Salix-Vaccinium Associes
Vaccinium consocies
Rubus consocies
Salia consocies
Epilobium-Cirsium AssociFS
Cirsium consocies
Epilobium consocies
Agrostis-Bromus AssociFS
Bromus consocies
Agrostis consocies
Funaria-Marchantia Associes
Marchantia consocies
Funaria consocies
There remains only to be considered briefly reproduction in
the burns in the northeastern part of the area and especially
along the Palouse River where the lodgepole pine plays a sig-
nificant rôle. The wide range of the lodgepole habitat from very
moist to very dry soil, its rapid growth and early reproduction as
well as its inability to withstand fires or to endure shade are too
well known to necessitate discussion here. - -
The forests of this part of the region, where lumbering oper-
ations have been going on for a long time and burns of all ages
occur, are mixed throughout with lodgepole pine, the amount of
which may vary from a few towering relict trees to nearly pure
stands. - :
:
i
*
&
99 - - • .
:
IOO A Study of the Vegetation of
In case of a limited but severe burn in the midst of a mixed
forest, provided a few lodgepole seed-trees are present, the fol-
lowing generation is usually predominated by the lodgepole pine.
Provided the various tree seedlings have an equal start, the lodge-
pole, because of its more rapid height-growth, gains an ascend-
ency over its neighbors. Likewise, by its habit of early repro-
duction (I have frequently found trees only seven years old bear-
ing cones) it furnishes seeds for any unoccupied areas or for the
entire area if seeds of other trees for any reason fail to be present.
I have seen a few such areas dominated by lodgepole pine bu
comparatively they are not abundant. ... - - -
But because of its early maturity and its inability to reproduce
in its own shade, in spite of the advantage gained in the middle-
aged forest, the lodgepole is the first tree to drop out of the
mature forest. Unless aided by another fire before its competitors
portant tree.
reproduce, it assumes a less and less important rôle. Indeed, in
most of the forests it occurs only as scattered individuals, al-
though, as previously stated, in areas cut and burned-over thirty
to fifty years ago the lodgepole pine is not infrequently an im-
THE HYDROSERE
We shall now take up the development of the hydrosere. An
outline of the vegetational units of this sere together with their
relation to the xerosere may be found on page 19. Because of
the peculiar topography of the region, combined with the arid
climate, hydrophytic and meso-hydrophytic communities are not
widely represented. However, along the streams and in small
ponds and lakes, the latter occurring especially in the north-
western part of the region, the following communities are found.
The three well marked associes of the water sere showing strik-
ing changes of habitat and life form as well as definite floristic
• *
• *
tºp
* *
* 9. tº
* @
differences, are those dominated by submerged, floating, and
swamp plants respectively, in their successional sequence. The
last, stage is succeeded by a wet meadow community which is
usually followed by a consociation of the Agropyron-Festuca
* = ..association but may be replaced by the flood-plain forest associes.
IOO . .
Southeastern Washington and Adjacent Idaho. IOI
The Chara-Potamogeton Associes
In shallow ponds and small clear streams it is not an unusual
sight to find the water rather completely filled with various sub-
merged plants, of which sometimes Chara and sometimes Pota-
mogeton pectinatus or P. californicus are dominant. Perhaps
there occurs more often a mictium of the dominants of the two
consocies respectively. - . . . .
In addition to Vaucheria, Stigeoclonium, and other algae, which
are frequently very abundant in such situations, Najas flewilis,
Zannichellia" palustris, and Batrachium aquatile, also help make
up the tangle of submerged plant life. . . . .
The water crowfoot shows great plasticity in its habitat re-
quirements, and as the ponds become shallower it is not unusual
to find it dominating considerable areas of muddy banks. The
aerial leaves with their well developed blades appear in striking
contrast to the filiform submerged ones.
The rôle of these submerged plants in the preparation of a
suitable substratum for later stages in succession is frequently
very marked. As a result of the dense aggregation of the indi-
viduals of the constituent species of this community, bodies of
water often exhibit a pronounced accumulation of debris consist-
ing for the most part of the remains of former generations of
aquatic plants and animals but mixed with fine soil particles
brought in by the action of wind and water, the whole being
effectively held in position by the expanding tangle of living
plants. The accumulation of humus decreases the total amount
of water in the substratum and the habitat gradually approaches
a little nearer the mesophytic. . As the bottom of the pond is
slowly raised by the accumulating debris, the substratum be-
comes relatively more compact. -
A continuation of these processes reacts unfavorably upon the
submerged plants and they thus prepare the way for their own
elimination. Not only is the reaction of initial stages of succes-
sion unfavorable to the pioneer plant community but it also actually.
favors invaders. Plants with slender stems and floating leaves,
such as Potamogeton and pond lilies, for a time take possession
IOI
Io2 A Study of the Vegetation of
of the shallowed water, while through the agency of further
humus accumulation, a suitable foothold is eventually afforded
for the development of cattails, sedges, rushes, and other mem-
bers of the marsh community. -
About the margins of shallow ponds and streams and often
growing in shallow water are to be found Mimulus langsdorfii,
Veronica spp., Radicula spp., Ranunculus alismaefolius, or Steiro-
nema ciliatum. If the ponds are larger, the shallower water near
the margins is often dominated by plants of the following com-
munity: - -
The Nymphaea-Potamogeton Associes
Typically this associes is composed of plants rooted in the mud
below but with a part or all of the leaves floating on the water
surface. Their general position in the sequence of succession is
following that of the submerged forms, whose reaction upon the
habitat, as previously pointed out, is to shallow the water and
thus make it less fit for themselves and more fit for the anchored
floating forms. -
The Marsilea community is well represented in certain small
ponds but is most conspicuous in the rock pockets in the beds of
streams during the dry season. The ability of Marsilea vestita
to float on the surface of water of varying depth or to live rooted
in the mud or even in rather dry soil fits it to occupy just such a
changing habitat. However, it is far less important than mem-
bers of the following consocies. - -
The Potamogeton consocies consists of various species of Pota-
mogeton of which P. americanus often is dominant (Fig. 29).
Frequently associated with it are the submerged P. pectinatus
and P. californicus. In late summer ponds containing the latter
species are sometimes margined for considerable distances from
the shore with the broadly expanded leaves and the dense spikes
of P. americanus. Associated with it are Polygonum amphibium
and the duckweeds, Lemma minor, L. trisulca, and locally, Spiro-
dela polyrhiza. - -
Other ponds and especially lagoons along the upper Palouse
River are characterized by an abundance of Nymphaea poly-
I O2
Southeastern Washington and Adjacent Idaho. IO3
sepala, whose broad leaves and pretty yellow flowers almost com-
pletely cover the water for many square meters (Fig. 30).
Additional floating-leaf aquatics are occasionally seen in mix-
ture with the lily. The commonest of these are species of
Potamogeton and Alisma plantago-aquatica. -
Where the current is swift enough during a part of the year
to keep the bottom relatively free from debris, the lily community
may continue for years. But by continued humus accumulation
and elevation of the bottom, the habitat becomes invaded more
and more completely by plants of the marsh community and
finally the lilies disappear entirely. -
The Scirpus- Typha Associes
Like the preceding, the associes characterized by Scirpus and
Typha is found covering only very limited areas considering the
region as a whole. I have rarely seen the two dominants grow-
ing together, and, in fact, Typha is not abundant. However, ob-
servations on Typha in its limited habitat together with a study
of its relict associates in shallow water show rather clearly its
place in the succession.
The Scirpus consocies is more widely represented. The domi-
nant species are the western tule, Scirpus occidentalis, and Scir-
pus microcarpus. While often growing in rather deep water
about lake margins where they are sometimes associated with
relict Nymphaea and Potamogeton, they likewise occupy boggy
places, which in late summer may become mere mud flats (Fig.
3I). Among the tall stems of the bulrushes is often revealed a
distinct layer of Alisma plantago-aquatica, Sagittaria arifolia,
and Mentha canadensis borealis, while among these various
species of creeping buttercups may be seen.
Sometimes, as at Tule Lake, a slightly higher and consequently
drier habitat gives a fine zonation of Eleocharis palustris and
other members of the Eleocharis-Carew community. The pres-
ence of the latter among the tule in the drier portions of its area
indicates the next stage of development. -
IO3
IC 4 - A Study of the Vegetation of
The Eleocharis-Carew Associes
This plant community covers areas along the flood plains of
smaller streams which are wet during the rainy season but often
quite dry during the late summer months. Likewise, about the
borders of lakes and springs it occupies situations of lower water
content than those characterized by Scirpus or Typha.
The Eleocharis consocies is dominated by E. palustris. It some-
times covers considerable areas with a pure growth (Fig. 31).
Its rhizomes form extensive mats which abound at the edge of
ponds as well as in the shallow water. Associated with it is E.
acicularis. It likewise has well developed and extensive root-
stocks, while those of E. acicularis bella are very short so that
the mats assume the form of dense round tufts. Because of its
lesser height-growth the latter species is easily distinguishable
from the former.
Frequently occurring in mixture with Eleocharis are various
sedges and rushes of the following community.
The Carew-Juncus Mictium.—I have never seen in this region
any considerable area dominated by one species of Carew or
Juncus. However, a study of the fragmentary areas charac-
terized by this community reveals the dominance of Carea ne-
braskensis and Juncus balticus locally. More often the follow-
ing species occur in a puzzling mictium: -
Carea lanuginosa Juncus bufonius
Carea monile pacifica Juncus ensifolius
Carew nebraskensis - Juncus suksdorfii
Carex pachystachya Juncus tenuis
Juncus balticus
In addition to relicts of the preceding communities, associated
with the above species are to be found numerous other plants of
which the most important are Beckmannia erucaeformis, Radic-
ula curvisiliqua, Alopecurus californicus, Epilobium adenocaulon,
Carew utriculata, and Mentha canadensis borealis. The last-
named plant is very important ecologically. It has well devel-
oped and extensive rhizomes. It not only thrives in very wet
IO4.
Southeastern Washington and Adjacent Idaho. IO5
situations but likewise occurs abundantly on the thin soil of the
stony bottoms of intermittent streams.
The Wet Meadozw Associes
The wet meadows occupy a zone lying intermediate in succes-
sion between the Eleocharis-Carew associes on the one hand and
the more mesophytic type of prairie on the other. As would be
anticipated, it shows all stages of the disappearance of relict
members of the Eleocharis-Carea community which it frequently
borders, as well as the invasion of the more mesophytic prairie
species.
However, the community as a whole is well defined and is es-
pecially characterized by numerous socies. These wet meadows
often occupy considerable areas, especially near the mountains,
and under cultivation furnish an excellent yield of timothy.
Omitting relicts of earlier communities, and many species
found typically on moist hillsides, the following list gives the
principal wet meadow species:
Species Forming Distinct Socies.—
Deschampsia caespitosa
Hookera hyacinthina
Heracleum lanatum
Iris missouriensis
Polygonum bistortoides
Other Species.—
Calochortus mitidus
Carea aperta
Castilleja miniata
Cicuta occidentalis
Cogswellia triternata
Delphinium simplex
Epilobium adenocaulon
Equisetum spp.
Galium boreale
Hordeum nodosum
IO5
Quamasia quamash
Ranunculus platyphyllus
Veratrum californicum
Wyethia amplexicaulis
Hypericum scouleri
Lupinus leucophyllus
Mentha canadensis borealis
Orthocarpus tenuifolius
Poa annua
Poa triflora
Polygonum emersum
Polygonum polygaloides
Potentilla rectiformus
Prunella vulgaris lanceolata
*
<!
:
º
*
º
•'
;
IO6 A Study of the Vegetation of
Rumer meanicanus Steironema ciliatum
Rumex occidentalis Trifolium douglasii
Senecio serra Zygadenus venenosus
Sidalcea oregana
In this region the associes is represented by a single consocies,
namely that dominated by Deschampsia caespitosa. This char-
acteristic grass with its densely tufted perennial stems, which
often reach a height of over 3 feet, often occurs in nearly pure
growth. In favorable situations, the clumps may reach a diame-
ter of 9 inches.
The Quamasia socies is well marked in the early spring when
large areas in the wet meadows are characterized by the dark
blue flowers of Quamasia quamash (Fig. 32). These scapose
plants, reaching a height of 2–2.5 feet, are terminated by elongated
racemose clusters of as many as 30 large, blue flowers. The in-
dividuals frequently occur as abundantly as 35–45 in a square
meter. The edible bulbs, which are nearly an inch in diameter and
buried only 4 inches in the soil, are a favorite food of the Indians.
Heracleum lanatum, the cow parsnip, is very abundant in wet
meadows along streams (Fig. 34). It not only reaches far above
other herbaceous vegetation, but its large size and numerous,
large, white-flowered umbels, which bloom for weeks, make this
socies a very conspicuous one for the major part of the growing
SeaSO11.
Wet meadows in early spring are characterized by the great
abundance of Ranunculus platyphyllus. Its great numbers, com-
bined with its profuse flowering habit, makes this socies one of
the most important of the vernal period. The plant has rather a
bushy habit. Growing about 2 feet high, it often spreads at the
top over a diameter of 3 or more square feet. The golden yellow
flowers are 2.5 centimeters in diameter. -
Many parts of the wet meadows are dominated by large areas
of Iris missouriensis. The growth habit of this cosmopolitan
species is too well known to need further comment here (Fig. 33).
The black sunflower, Wyethia amplexicaulis, often found in
rather dry prairies, is typically at home in the wet meadows.
• * * IO6
ºr
• * * * *
* * & ©
• * • ‘p
º *
*
Southeastern Washington and Adjacent Idaho. Io?
Often the gregarious growths almost exclude other plants. Its
large, dark-green, shiny, resinous leaves, more than a foot long
and as many as 20 on a single individual, are no less characteris-
tic than its numerous, large yellow flowers. A single plant may
occupy an area of more than 2 square feet although 20–30 plants
often occur in a single quadrat. It possesses a strong tap root,
5–9 inches in circumference, which may penetrate the soil to a
depth of over 6 feet.
The wet meadow is gradually replaced upon its higher lying
borders by typical prairie species.
It should be mentioned in this place that in the drier regions
large areas of low-lying ground are dominated by dense growths
of rye-grasses, especially Elymus condensatus. In low ground
such as dried basins of shallow ponds and where the soil is alka-
line, socies of salt grass, Distichilis spicata, or of Spartina gracilis
are to be found.
The Flood-plain Forest Associes
The flood-plains along the streams, because of the seasonal dis-
tribution of the precipitation, are peculiarly apt to be subjected to
periodical submergence. Growing in these rich, well-watered,
alluvial soils are to be found dense thickets of various trees and
shrubs and occasional groves of poplars and aspens. Since the
larger streams soon cut canyons into the basalt, the flood-plains
are usually not extensive and the zone of tree growth is often
limited, especially westward, to a mere fringe along the bank of
the streams (Fig. 35). Likewise many of the smaller streams
are intermittent and along these thickets of woody species are
few or entirely absent. A close relationship exists between the
protection from wind, afforded flood-plain areas by canyon walls
and hills, and the presence or absence of trees and shrubs.
Although these flood-plain species usually occur in various
mictia, however, two communities are rather well defined—the
Populus consocies and the Salix-Crataegus mictium.
The Populus Consocies.—Small groves of poplars consisting
of Populus tremuloides, or more rarely of Populus trichocarpa
are frequent along the flood plains, especially in the less arid parts
Io/
IO8 A Study of the Vegetation of
of the region. These usually occur in situations where the stream
has a double channel or where, having abandoned one channel, it
has built up a rich alluvial flat. It is quite clear how after a
spring flood the wind-blown seeds of the poplars find excellent
conditions for germination in such situations and even if only a
few become established the extensive underground parts of Popu-
lus tremuloides would soon increase the area dominated by trees.
In this manner the trembling aspen frequently extends its terri-
tory beyond the flood-plain onto the moist, sheltered banks of
canyons. I have observed one or two cases in the deeper canyons
where yellow pines had established themselves among the aspens,
and seemed to be replacing them.
The Salia-Crataegus Mictium.—Much larger areas of the flood-
plains are dominated by shrubs or trees of the following species;
these may occur singly, but more often form a mictium.
Alnus tenuifolia Salix bebbiana
Amelanchier florida Salia cordata
Crataegus brevispina Salia exigua
Prunus demissa Salix scouleriana
Salia argophylla
In addition to the above dominants numerous secondary tree
species and several important undershrubs should be mentioned
here. The following are the most important:
Alnus rhombifolia Rosa pisodarpa
Amelanchier cusickii Ribes aureum
Betula microphylla Salix bella
Cornus stolonifera Salia lasiandra caudata
Crataegus columbiana piperi Salix pyrifolia
Rosa nutkana
The alder sometimes becomes so abundant locally as to consti-
tute perhaps half of the flood-plain woody vegetation. The
chokecherry is never so abundant.
Of the willows, only one, Salia lasiandra caudata, assumes the
proportions of a tree. As might be anticipated, the willows are
usually among the first species to appear.
IO8
Southeastern Washington and Adjacent Idaho. IO9
Crataegus brevispina and Amelanchier florida form dense
thickets, sometimes singly, but more often in mictium. Fre-
quently these copses are so dense as to exclude all other vegeta-
tion. In the month of May when these trees are clothed with
their profuse white blossoms the flood-plains are indeed a beauti-
ful sight. Even in winter the woodland growth along the
streams, as they wind their way among the treeless hills, lends
pleasing variety to the monotonous landscape.
RUDERAL VEGETATION
There are a number of plants that are regularly found in and
about waste places. To this number may be added others that
are regular members of certain of the preceding plant communi-
ties which now and then reveal a decidedly ruderal tendency.
The following list includes the commoner plants of this nature:
RUDERAL SPECIES
Amaranthus blitoides Dipsacus sylvestris
Amaranthus graecizans Erigeron canadensis
Amaranthus retroflexus Erodium cicutarium
Amsinckia intermedia Geranium pusillum
Anthemis cotula Madia glomerata
Arctium lappa Marrubium vulgare
Artemisia atomifera Matricaria matricarioides
Artemisia gnaphalodes Polygonum aviculare
Bromus brigaeformis Salsola kali tenuifolia
Chenopodium botrys Sanguisorba annua
Chenopodium album Sisymbrium altissimum
Cirsium lanceolatum Vaccaria vaccaria
Collinsia tenella { Verbascum thapsus
Because of the practice of alternating a crop of wheat with
summer fallow nearly half of the farmed area is laid bare each
year for the invasion of ruderals. Amaranthus graecizans and
A. retroflexus are the dominant weeds of these fallow fields.
Unless the ground is frequently tilled these grow in great abun-
dance, the former breaking loose near the surface of the soil in
IO9
I IO - A Study of the Vegetation of
the fall of the year and tumbling over the ground, is piled by the
wind into great heaps on the leeward slopes of the hills.
Westward, in the drier regions, and especially in the scab-lands,
Sisymbrium altissimum, locally known as Jim Hill mustard, from
its introduction along the right of way of the railroads, is pres-
ent to a degree almost unbelievable. Hundreds of acres in the
scab-lands are literally “taken” by this weed. From dwarfed
specimens a few centimeters high on the scab-rock, it ranges to
rank growths in the moist soil. It is a bad weed in the wheat
fields throughout the greater part of the region.
The tar weed, Amsinckia intermedia, is likewise a troublesome
weed along roadsides and especially in wheat fields. South of
Snake River it is very abundant. Its dense coat of long bristly
hairs upon drying becomes extremely annoying to both men and
horses. -
Westward and especially in the slightly alkali regions the Rus-
sian thistle, Salsola kali tenuifolia, and the Australian salt bush,
Atriplex semibaccata, are often abundant.
Dipsacus sylvestris, introduced a number of years ago, has
spread very rapidly and in many localities assumes the rôle of a
very thrifty and very obnoxious weed. *
The little geranium, Erodium cicutarium, is an introduced
weed which has become very common in gardens, feed lots, and
waste places. Often associated with it are Sanguisorba annua,
Geranium pusillum, and Verbascum thapsus.
Common roadside weeds of especial abundance are Madia
glomerata, Marrubium vulgare, and the rattle grass, Bromus
brigaeformis. The absence of most roadside weeds so common in
the eastern and central states is very characteristic.
About the numerous grain-loading stations throughout the
region many ruderals are gaining a foothold. Here the cars are
swept out and the seeds of various plant species scattered.
Among other weeds thus recently introduced, and which I have
seldom seen elsewhere, may be mentioned Ambrosia trifida, A.
psilostachya, Melilotus alba, M. officinalis, Cirsium arvense, Iva
aranthifolia, Datura tatula, and Datura stramonium. The prob-
lem of grain warehouses as centers of weed distribution would
I IO
Southeastern Washington and Adjacent Idaho. I I I
form in itself an intensely interesting and very practical field of
investigation.
CONCLUSION
In the foregoing pages it has been shown that in this region
lying in southeastern Washington and adjacent Idaho, three plant
formations occur. In the western part of the region, that of least
elevation and consequently of lowest precipitation, the desert
scrub formation occurs. As the altitude becomes greater and the
climatic conditions more favorable eastward, the desert scrub
gives way to the grass land of the prairie-plains formation. In
its early development this grassland is of a very open bunch-grass
type, with much of the ground being either destitute of vegeta-
tion or carpeted with interstitial plants only in early spring. As
conditions become less xerophytic at higher altitudes the ground
becomes rather completely occupied by grasses, some of which
are sod-formers, and by non-grassy herbaceous vegetation which
shows a great increase both in the number of species and in the
number of individuals per unit area. The best developed prairies
reveal a potential shrub community which, while held in check
usually by competition with prairie plants, develops in the eastern
edge of the grass lands and especially upon the non-basaltic soils
into thickets of chaparral. Under cover of the chaparral, the
yellow pine, a pioneer community in the development of the
Pacific Coast forests, often becomes established. The pine may
be replaced by Douglas fir and tamarack, and these in turn by
mixed communities dominated by tamarack and white fir, or by
white fir and cedar. Finally, in the most mesophytic areas the
cedar community reveals the climax stage in the development of
the Pacific Coast forest formation. g
It has been shown that the desert scrub formation is charac-
terized by soils with lower water content and higher temperature,
and with higher evaporating power of the air than any of the
other plant communities. Likewise, there has also been found to
exist in the several plant communities of the xerosere, from the
bunch-grass community of the prairies to the climax cedar com-
munity of the forest, a direct relation between the water content
I I I
I I 2 A Study of the Vegetation of
of the soil, the temperature of the soil and the evaporating power
of the air, and progressive stages in succession. The water con-
tent of the soil has been found to vary directly with the stages of
the sere from a minimum in the bunch-grass stage to a maximum
in the cedar community. Conversely, the soil temperature and
the evaporating power of the air have been shown to decrease
directly in proportion to the advancement of the stage of develop-
ment of the sere.
In the forest communities the light values decrease progress-
ively as the climax community is approached.
In addition to the xerosere, beginning with lichens and mosses
on the bare rocks of basalt, granite, or quartzite and ending ulti-
mately in the climax forest community, we have also traced the
stages of the subsere in the reëstablishment of cut-over or burned-
over forested areas. We have seen how these more or less de-
nuded areas may finally come to support the same type of vegeta-
tion that characterized them before the disturbance of their
normal development.
Lastly, we have considered the hydrosere. The communities of
this sere, although occupying a relatively small area geograph-
ically, show distinct stages from the submerged, floating and
swamp communities to that of the wet meadow. The latter is
usually replaced by a xerophytic grass land community, or infre-
quently by a deciduous flood-plain forest.
In concluding this report on the study of the vegetation of
southeastern Washington and adjacent Idaho, the writer wishes
to state that perhaps no one feels more keenly than he the neces-
sarily preliminary nature of the work accomplished.
The Snake River Canyon alone, with its peculiarly dry, mild
climate stands in marked contrast to the colder, more humid area
above, and forms a rich field for detailed ecological investigation.
Not infrequently has the writer spent days in late February or
early March among the abundant prevernal flora of the canyon,
while weeks later most of the same species came into blossom on
the plateau above, while yet another period elapsed before the
awakening of the same species on butte and mountain prairies.
During the progress of this study a number of plant species
II 2
Southeastern W ashington and Adjacent Idaho. I 13
not reported for the region were encountered. Among these the
occurrence of the devil's club, Echinopanax horridum, along cer-
tain streams in Thatuna Hills, is especially interesting. Many
of the species new to the region are ruderals. Other plants like
Crataegus columbiana piperi, heretofore known to occur only in
Washington, were also repeatedly found in Idaho.
It is hoped that the results of the present research may form
a basis for further investigation of the ecological problems of
this and adjoining regions.
IO.
II.
I2.
I3.
I4.
I5.
LITERATURE CITED
. Calkins, F. C. Geology and Water Resources of a Portion of East-
central Washington. Water-supply paper U. S. Geological Survey
No. II8, 1905.
. Clements, F. E. Plant Succession. Carnegie Inst, Wash. Publ., 242,
1916.
. Frye, Theodore C., and Rigg, George B. Northwest Flora, 1912.
. Fuller, George Damon. Evaporation and Plant Succession. Bot. Gaz.,
52: I93–208, IQII.
. Fuller, George Damon. Evaporation and Soil Moisture in Relation
to Succession of Plant Associations. Bot. Gaz., 58: 193–234, 1914.
. Humphrey, Harry B., and Weaver, John Ernst. Natural Reforesta-
tion in the Mountains of Northern Idaho. Plant World, 18; 31–48,
IQIS.
. Hoffman, Julius V. Natural Reproduction of Coniferous Forests.
Univ. Minn. Studies Biol. Sci., I.
. Landes, Henry. Underground Waters of Washington. Water-supply
and Irrigation Paper, No. III, 1905.
. Piper, Charles V. Flora of the State of Washington. Contributions
from the U. S. National Herbarium, II : 1906. -
Piper, Charles V., and Beattie, R. Kent. Flora of the Palouse Region,
IQOI.
Piper, Charles V., and Beattie, R. Kent. Flora of Southeastern Wash-
ington and Adjacent Idaho, 1914.
Russell, I. C. Principal Features of the Geology of Southeastern
Washington. Mining, 3: I63–165, 1897.
Russell, I. C. Reconnaissance in Southeastern Washington. U. S.
Geol. Surv., Water-supply and Irrigation Paper No. 4, 1897.
Russell, I. C. Geology and Water Resources of the Snake River
Plains of Idaho. Bull. U. S. Geol. Surv., No. 199, 1902.
Turesson, G. Slope Exposure as a Factor in the Distribution of
II 3
I I4. A Study of the Vegetation of
Pseudotsuga taxifolia in Eastern Washington. Bull. Torr. Bot.
Club, 41 : 337-345, 1914.
16. Weaver, John Ernst. Evaporation and Plant Succession in South-
eastern Washington and Adjacent Idaho. Plant World, 17: 273–
294, IQI4.
17. Weaver, John Ernst. A Study of the Root-systems of Prairie Plants
of Southeastern Washington. Plant World, 18: 227–248 and 273–
292, IQI5.
18. Whitford, H. N. The Forests of the Flathead Valley, Montana. Bot.
Gaz., 39: 99–122, 194–218, 276–296, 1905.
I (4
FIG. 16. Typical view in the sagebrush community. The chief plant is
the scab-land sage, Artemisia rigida. The hills in the background are
covered with bunch-grass.
FIG. 17. A glimpse of the lichen-moss community. The black mats are:
Grimmia montana. Surrounding the base of the rocks and extending along
the deeper crevices are patches of Tortula into which the June grass is
invading.


Fig. 18. June grass and knotgrass on thin rocky soil.
Note the bunch-
grass occupying the deeper soil in the background.
19. A typical bunch-grass community.
Much of the soil surface is
unoccupied.


Fig. 20. A hillside in Garfield County clothed with plants of the Agropyron
consociation. Typical representation of the drier type of prairie.
Fig. 21. Festuca consociation in eastern Whitman County; representative"
of the less xerophytic type of prairie.


FIG. 22. Minor quadrat in the Festuca consociation. The conspicuous
plants are Balsamorhiza sagittata, Hieracium scouleri, and Festuca ovina
ingrata.
* “Frg. 23. Yellow pines invading a protected north slope under cover of
the ninebark, Opulaster pauciflorus. The exposed south slope is covered
with prairie, tongues of which extend down the dry ridges shown in the
picture.



Southeastern Washington and Adjacent Idaho.I 19
Fig. 24. Yellow pines in a ravine and on an exposed slope.
I 19

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- -
FIG. 25. Douglas fir and yellow pine on an exposed rocky slope in the
mountains.
Fig. 26. A mixed forest of Douglas fir, tamarack, and white fir.


Southeastern Washington and Adjacent Idaho.
Fig. 27. A glimpse into a primeval forest of Laria, Abies, and Thuj
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FIG. 28. Climax Thuja consociation. In such situations the light is too
low to permit the growth of tree seedlings other than the cedar.
Fig. 29. Potamogeton consocies in Silver Lake.
Potamogeton americanus.
The chief species is
Willows fringe the margin of the lake.


Fig. 30. A consocies of Nymphaea in a lagoon of the Palouse River.
Fig. 31. View near Rock Lake showing zonation of Eleocharis pal
tris (foreground) and Scirpus microcarpus. In the background are flood-
plain trees of willow, hawthorne, and Amelanchier.


FIG. 32.
A wet meadow socies of Quamasia quamash.
FIG. 33. A socies of Iris missouriensis.


Southeastern Washington and Adjacent Idaho. I 25
Fig. 34. Heracleum lanatum and Crataegus brevispina in a wet meadow.
Fig. 35. A view of the flood-plain trees along Rock Creek in western tº
Whitman County. The chief trees are Betula microphylla, Crataegus brevi-
spina, and species of Salir,
i


FIG. 36. A view of Kamiak Mountain looking northward from Smoot
Hill. Note the fringe of pines near the summit of the exposed south
slope.
FIG. 37. The north slope of Kamiak Mountain. It is covered with a
second-growth forest of Douglas fir and tamarack.


Fig. 38. A bit of skyline at Pullman, Washington, showing the rounded,
flowing outlines of the dune-like topography.
FIG. 39. A view in the scab-lands in eastern Adams County. A dis-
tance of a few feet may show a change of vegetation from the lichens and
mosses on the rocks to the June grass—knot-grass or sagebrush com-
munities. Likewise, the bunch-grass and balsam-root of the drier soil
gives way to more mesophytic species in the depressions.
Fig. 40. A family of knot-grass invading a newly formed talus"slópe.



:
-
Fig. 42. A single plant of Balsamorhiza sagittata.
:

pical representation of the
I 29
A ty
11 developed mixed forest.
destruction by fire of the coniferous forests of the Northwest.
An old burn in a we
Fig. 43.

A Study of the Vegetation of
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Under
the cover of the fireweed numerous seedlings of yellow pine, Douglas fir,
-year-old burn on a dry slope in Thatuna Hills.
and tamarack are to be found.
A five
FIG. 44.
I 30

2
--
Fig. 45. Rock Lake near Spokane, Washington. The thin basaltic
Pinus ponderosa and, in more sheltered places, Pseudotsuga mucronata.
soil supports an open growth of
(Photograph by Palmer.)
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2

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Fig. 46. A sharp ecotone between prairie and forest on a wind-swept
slope in Tekoa Mountains.
FIG. 47. The bunch-grass, Agropyron spicatum. Diagrammatic cross-
section and detailed segment of a leaf showing its xerophytic anatomical
Structures.


f one of
ta. The cross-section o
ingra
Bunches of Festuca ovina
Fig. 48.
the setaceous leaves shows that it is well adapted to endure drought.

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