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Issued September 20, 1911.
U. S. DEPARTMENT OF AGRICULTURE,
FOREST SERVICE BULLETIN 75.
HENRY S. GRAVES, Forester.
CALIFORNIA TANBARK OAK.
PART I. Tanbark Oak and the Tanning Industry.
By WILLIS LINN JEPSON, Collaborator.
t*
PART II. Utilization of the Wood of Tanbark Oak.
By H. S. BETTS, Engineer in Timber Testa, . (
APPENDIX. Distribution of Tannin in Tanbark Ok*. : '
By C. D. MELL, Assistant Dendrologist;' * / :
SEC
OCT 29 1914
Division of Forestry
University of California
WASHINGTON:
GOVERNMENT PRINTING OFFICE.
1911.
LETTER OF TRANSMITTAI,
U. S. DEPARTMENT OF AGRICULTURE,
FOREST SERVICE,
'./ : I/: : : Washington, D. C., March 13, 1911.
*SiR: 1 have., the honor to transmit herewith a manuscript entitled
!?tCaJffiryia.'Ta2jbark Oak/' by Willis Linn Jepson, collaborator, and
H. S. Betts, engineer in timber tests, together with an Appendix by
C. D. Mell, assistant dendrologist, and to recommend its publication
as Bulletin 75 of the Forest Service. This bulletin shows how the
complete product of tanbark oak its bark and its wood may be
utilized. It is important that this complete utilization should be
brought about. The wood is now left in the forest to rot unused or
to add fuel to forest fires. The timber tests show that the lumber
has a high value and can be put to the same uses to which the eastern
oaks are put. A careful handling of woodlands, coupled with con-
servative lumbering, ought to make the tanbark-oak crop continuous
and render this resource inexhaustible.
Respectfully, . HENRY S. GRAVES,
Forester,
Hon. JAMES WILSON,
Secretary of Agriculture,
2
CONTENTS. \
PART I. TANBARK OAK AND THE TANNING INDUSTRY.
Page.
Development of the tanning industry in California 5
Silvical characteristics of the tanbark oak 6
Range and occurrence 7
Associates 8
The production of tanbark 8
Centers of the industry 8
Stand and yield 9
Peeling 10
Transportation 12
Quality of the bark 14
Prolonging the supply 15
Providing for second growth 16
Sprout reproduction 16
Reproduction by seed 17
Second-growth bark 17
Quality of second-growth bark 18
Conservative methods in the woods 19
Guarding against fire 19
Tannin-extract processes 20
Supplemental materials 21
Possibilities of utilizing the wood 22
Conclusions 23
PART II. UTILIZATION OF THE WOOD OF TANBARK OAK.
Tanbark oak lumber 24
Appearance and characteristics of the wood 24
Strength '. 25
Seasoning 28
Shrinkage 29
Hardwoods used on the coast 30
Suggested uses for tanbark oak 31
APPENDIX.
Distribution of tannin in tanbark oak 33
3
477598
:
LETTER OF TRANSMITTAL
U. S. DEPARTMENT OF AGRICULTURE,
FOREST SERVICE,
\: /: * Washington, D. C., March 13, 1911.
"SiR* 1 have.4he honor to transmit herewith a manuscript entitled
t^*ta!ifC)riiia."Tai?bark Oak/' by Willis Linn Jepson, collaborator, and
TEE S. Betts, engineer in timber tests, together with an Appendix by
C. D. Mell, assistant dendrologist, and to recommend its publication
as Bulletin 75 of the Forest Service. This bulletin shows how the
complete product of tanbark oak its bark and its wood may be
utilized. It is important that this complete utilization should be
brought about. The wood is now left in the forest to rot unused or
to add fuel to forest fires. The timber tests show that the lumber
has a high value and can be put to the same uses to which the eastern
oaks are put. A careful handling of woodlands, coupled with con-
servative lumbering, ought to make the tanbark-oak crop continuous
and render this resource inexhaustible.
Respectfully, . HENRY S. GRAVES,
Forester.
Hon. JAMES WILSON,
Secretary of Agriculture,
2
CONTENTS. \
PART I. TANBARK OAK AND THE TANNING INDUSTRY.
Page.
Development of the tanning industry in California 5
Silvical characteristics of the tanbark oak 6
Range and occurrence 7
Associates 8
The production of tanbark 8
Centers of the industry 8
Stand and yield 9
Peeling 10
Transportation 12
Quality of the bark 14
Prolonging the supply 15
Providing for second growth 16
Sprout reproduction 16
Reproduction by seed 17
Second-growth bark 17
Quality of second-growth bark 18
Conservative methods in the w r oods 19
Guarding against fire 19
Tannin-extract processes 20
Supplemental materials 21
Possibilities of utilizing the wood 22
Conclusions 23
PART II. UTILIZATION OF THE WOOD OF TANBARK OAK.
Tanbark oak lumber 24
Appearance ajid characteristics of the wood 24
Strength '. 25
Seasoning 28
Shrinkage 29
Hardwoods used on the coast 30
Suggested uses for tanbark oak 31
APPENDIX.
Distribution of tannin in tanbark oak 33
3
477598
ILLUSTRATIONS.
PLATES.
Page.
PLATE I. What is left after the tanbark is removed Frontispiece.
II. Typical tanbark oak country where, in the redwood belt, the tree
attains its best development 8
III. Fig. 1. Typical tanbark oak tree undergoing removal of first ring of
bark. Fig. 2. Closer view of the operation 12
IV. Fig. 1. Peeling 4-foot rings of bark from the felled tree. Fig. 2.
Bunching the bark in small piles along the sled road 12
V. Fig. 1. The skid ways to which the bunched bark is sledded, and
from which it is hauled to the railroad. Fig. 2. Hauling the bark
in wagons from the skidways to the cars 12
VI. Fig. 1. Machine and method used for testing small beams. Fig. 2.
Seasoning checks in the butt of a tanbark oak log exposed to the hot
sun for six weeks 24
VII. Fig. 1. Tanbark oak lumber for car construction. Fig. 2. Tan-
bark oak boards air-drying 24
VIII. Fig. 1. Tanbark oak flooring, and the method of storing and sorting it.
Fig. 2. Tanbark oak flooring ready for shipment from the mill. . 28
IX. Transverse section of a 2-year-old twig of tanbark oak, showing tannin
in the pith, pith-rays, and bark 28
X. Fig. 1. Transverse section of a 3-year-old twig of tanbark oak, show-
ing the distribution of tannin in the pith and pith -rays. Fig. 2.
Longitudinal radial section of a 3-year-old twig 28
4
uu
OCT 29 1914
Division of Forestry
University of California
CALIFORNIA TAN BARK OAK.
a)
PART I. TANBARK OAK AND THE TANNING INDUSTRY, 1
By WILLIS LINN JEPSON.
DEVELOPMENT OF THE TANNING INDUSTRY IN CALIFORNIA.
Tanbark oak is, economically, the most important of the 15 Pacific
coast oaks, because it furnishes the chief material used in the exten-
sive tanning industry of that region. In 1900, according to the
census, California ranked third among the States in the value of
tanned hides produced. Commercial tanning on the Pacific coast
began with the influx of Americans into California in 1849 and 1850.
As early as 1852 Sonoma County had one tannery which produced
$30,000 worth of leather, and by 1856 there were 18 in the State, in
which $94,000 was invested. The bark of the tanbark oak was first
used at Santa Cruz, and in 1857 a tannery there with an output of
700 hides a month was the largest in the State. Its leather was
superior to that produced by the establishments which still used the
live-oak and black-oak bark, the first utilized. By 1859 there were
29 tanneries and their product was more than sufficient for home
consumption. In the next year the value of the output of the State's
tanneries was $276,014, and seven years later, in 1867, there were
more than 40 establishments, with an annual product worth $400,000.
The development of the tanbark industry since 1850 is shown by
Table 1.
TABLE I. Tan oak bark harvested in California, 1855 to 1907.
Annual product.
Annual product.
Product by periods.
Year.
Cords.
Yar.
Cords.
Years.
Cords.
1855
1,000
3,000
8,000
15,000
21,000
24,000
24,000
1893
20,000
20,000
25,000
30,000
25,000
30,000
20,000
1851-1860
15,000
.55,000
147,500
240,000
218,500
185,000
861,000
1860
1895
1861-1870
1870.. .
1900
1871-1880
1875
1904
1881 1890
1880
1905
1891-1900
1881
1906
1901-1907 (7 years)
1851-1907
1890
1907
i In gathering the data upon which this report is based the author received assistance and helpful courte-
sies from many people directly or indirectly connected with the tanbark industry on the Pacific coast.
Their number was too great to permit of individual acknowledgment here, but the author takes this means
to thank them for the great assistance given him.
5
CALIFORNIA TAXBARK OAK.
At $18 per cord, an average of the prices since 1850, the value of
the bark produced in the period 1851-1907 would be $15,498,000.
Practically all of this has been consumed in the manufacture of heavy
leather used for belting, harness, saddles, and soles. The California
tanneries, up to 1907, turned out 250,000,000 pounds of such leather,
valued at $75,000,000.
SILVICAL CHARACTERISTICS OF THE TANBARK OAK.
Tanbark oak (Quercus densiflora H. & A.) grows to be from 50 to
140 feet high and from 1 to 6 feet in diameter. There are four general
forms of growth the roundheaded; the spire-shaped, similar to coni-
ferous trees; the shrubby, deep-shade form; and the stunted cha-
parral form. In open situations, or in association with madrona and
California black oak, the main trunk subdivides into a number of
large branches and forms a rounded head, although the height of the
crown is greater than its width. In dense, coniferous forests it
assumes the spire or cone shape of the trees with which it is associated,
and these trees are tallest and have the straightest trunks, with a
clear length of from 30 to 80 feet. Under stands of mature Douglas
fir or redwood there may be abundant low, shrubby growths of tan-
bark oak, since the tree is remarkably shade enduring, and when the
dominant forest cover is removed the tanbark oak promptly takes
possession of the logged areas. This is exemplified especially on the
Mendocino coast. In the interior of California, around Mount Shasta,
the stunted tanbark oak in the midst of chaparral assumes many of
the characteristics of the shrubs by which it is surrounded, such as
low stature, rigid branches, and small, thin leaves. This chaparral
form (var. ecJiinoides) is worthless for tanbark.
Tanbark oak has many chestnutlike characteristics. In the
character of its male flowers the tree is a chestnut, but in the character
of its female flowers and in its habit it is an oak. By some authors
it is referred to the genus Pasania, which includes nearly 1 00 species
in southwestern Asia.
The oaklike characters and the chestnutlike characters are com-
pared in the following tabulation:
CHESTNUTLIKE CHARACTERS.
Parallel nerves of the toothed leaves.
Erect catkins.
Pistillate flowers in same catkins as
staminate.
Stamens of male flowers very much ex-
ceeding calyx; rudiments of stamens in
pistillate flower.
A. corns with suggestion of burriness. Nut
often vaguely triangular.
OAKLIKE CHARACTERS.
Bark very like typical oak bark.
Involucre 1-flowered.
Ovary 3-celled.
Cup of the acorn a true cup and not a
closed involucre. Kernel oaklike, bit-
ter to the taste.
SILVICAL CHARACTERISTICS. 7
The chestnutlike leaves are from 2 to 5 inches long and are borne
on short petioles. The teeth are small and scattered. Sometimes
the margin is entire near the base or even for its whole extent,
especially on narrow-leaved forms. This variation in leaf form
sometimes leads woodsmen to speak of "two kinds of tanbark oak."
Both surfaces of the leaf, especially the lower, are covered with a
thick, light-colored, dusty fuzz, which gives the foliage a distinctive
hue.
The flowers, which appear in July or August, often conceal the
foliage with a mass of grayish-white blossoms. The acorns are
from f inch to 1J inches long, and from f to 1 inch broad, and coated
with a brown fuzz. The somewhat burrlike but shallow cup is
covered with long and narrow scales.
The bark of the trunk of adult trees is usually from 1 to 3 inches
thick, and sometimes from 4 to 5 inches; it is brown, smooth on
the surface, but so fissured longitudinally and transversely as to
produce elongated, irregularly rectangular plates. On the main
limbs and on young trunks the bark is very smooth, little fissured,
if at all, white, gray, or mottled, and often strikingly similar to the
bark of red alder.
RANGE AND OCCURRENCE.
The range of tanbark oak extends from a little north of the
Umpqua River in southwestern Oregon through the coast ranges to
Santa Barbara in California, and from the Humboldt region eastward
by way of the Shasta Mountains to the Sierra Nevada, and along
that range as far south as El Dorado County.
In general, though not always, tanbark oak grows either with
redwood or in the neighborhood of the redwood belt. It is an
associate of redwood in all the great redwood areas and even in the
isolated bodies or tongues in the range of that tree. The greatest
forests of redwood are in Mendocino and Humboldt Counties, and
in those counties tanbark oak attains its best development. (PL II.)
Tanbark oak is not at its best, however, in the heart of the redwood
forests, but in the belts which border them. The principal body of
tanbark oak forms a band along the inland side of the redwood belt
and covers the "Bald Hills." The general term "Bald Hills"
is a widely used folk name for the inland portion of the seaward Coast
Range, that much-broken mountain range which parallels the coast
and separates the ocean from such valleys as those of Santa Rosa,
Alexander, and Ukiah^nd the narrow canyon of the main Eel River
in its long course from Little Lake Valley northward to Humboldt.
The higher inner ridges and summits and the interior slopes are
covered by a mixed forest forming the tanbark oak belt along the
whole length of the main redwood body. In southern Humboldt,
8 CALIFORNIA TANBARK OAK.
however, the tanbark oak belt pushes through the great transverse
break in the redwood belt at that point, and an arm extends north-
ward over the Wilder Ridge country to the Rainbow Range. This
extensive and excellent virgin body borders the redwood belt on the
outside and covers a considerable portion of the Mattole country
lying between the redwood belt and the ocean.
In the region around Eureka the redwood stand is so exceedingly
dense that it practically occupies the whole country to the exclusion
of tanbark oak. In the redwood forests along the main Eel River,
on the Mad River, and on Smith River tanbark oak grows not at all
or merely as tare individuals. Here it is necessary to pass through
the redwood belt, or, what is usually the same thing, to gain the
summits of the ridges at the headwaters of the coast streams, to
find tanbark oak. To the south this is not the case. In Mendocino
County tanbark oak occurs throughout the redwood belt. There,
however, tanbark oak trees in the main redwood stands areisually
small and scattering, and it is only on the summits above the redwood,
and particularly on the inner summits and ridges, that the trees are
abundant and of large size.
ASSOCIATES.
Tanbark oak never forms a pure stand. The tanbark oak belt
consists of a mixed forest of broadleaf and coniferous trees. Its
most common associates besides redwood are Douglas fir, which,
except in Santa Barbara County, occurs with it throughout its
range; madrofia (Arbutus menziesii), its most common associate,
which reaches very large dimensions in the tanbark oak belt; Oregon
post oak (Quercus garryana), the most abundant of the true oaks in the
whole tanbark oak belt; California black oak (Quercus calif ornica) ,
on all the higher ridges, or high, fertile hill slopes; and western
chinquapin (Castanopsis chrysophylla) , an associate in the regions of
its best development.
THE PRODUCTION OF TANBABK.
CENTERS OF THE INDUSTRY.
The Santa Cruz district has been, from the first, one of the most
important sources of tanbark, because the tanneries at Santa Cruz,
San Jose, Santa Clara, and Redwood City could be supplied by
wagons direct from the woods, and this obviated long and costly
shipment by rail or water. Seventy-five per cent of the original
stand has been peeled, but recently second-growth trees have begun
to furnish a bark which is acceptable to tanners. Sonoma County
has been an important source for 30 or 40 years, and its status
now is about the same as that of the Santa Cruz district. For the
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE II.
OCT29I9I4
of Forestry
PRODUCTION OF TANBARK. 9
last 17 years the chief source has been the Mendocino district, along
the coast to the north of Sonoma, where tanbark has been outranked
only by redwood as a valuable forest product. This region has
furnished probably more bark than all others put together, but 45
per cent of the stand has been peeled now and a considerable portion
of the remainder is, under present conditions, too inaccessible to be
of value. The stand in the Santa Lucia Mountain region, along the
coast in Monterey County, which, though of excellent quality, was
never large, is now almost exhausted. In the isolated Santa Bar-
bara district and in the Sierra Nevada territory the trees are few and
scattered.
The most extensive bodies of virgin tanbark oak now are in the
north in northern Mendocino and Humboldt Counties and because
of accessibility to shipping the main sources of supply are in the coast
region of Mendocino, southern Humboldt, and, to some extent,
Sonoma Counties in California, and in southwestern Oregon. The
Sonoma and Mendocino areas have been drawn upon from the inte-
rior, also, by a railroad which follows the valleys of Santa Rosa,
Russian River, and Little Lake northward, and has now reached
the center of Mendocino County. The most northern part of the belt
has not been much disturbed, since the railroad has not reached it
and its distance from the ocean necessitates a long haul. The tan-
neries at Humboldt Bay have been supplied from Kneeland Prairie
and the Acorn region in the Bald Hills country.
STAND AND YIELD.
It is estimated that 'there are now 1,425,000 cords of standing bark
in the Pacific coast forests, distributed as follows:
Counties.
Cords.
California:
San Mateo, Santa Cruz, and Monterey
Marin, Sonoma, and Napa
Mendocino . :
Humboldt, Trinity, western Siskiyou, and Del Norte
Oregon:
100,000
70,000
320,000
87,5,000
Curry and Coos.
60,000
Total..
1,425,000
At the present rate of consumption, this is enough to provide for
the needs of the leather industry in California for a little less than
half a century.
The average yield of bark is from 200 to 350 cords per "claim,"
or quarter section (from 1J to 2^ cords per acre). From 350 to 640
cords (from 2J to 4 cords per acre) is considered a particularly good
yield, and exceptionally fine quarter sections yield from 640 to 1,200
cords (from 4 to 7J cords per acre). The highest yields are not
89446 Bull 7511 2
10
CALIFORNIA TANBARK OAK.
uncommon in the best parts of the southern Humboldt and northern
Mendocino district, where the stand in limited areas is nearly pure
tanbark oak. The largest amount of bark ever reported from* one
"claim" was 1 ; 284 cords, or 8 cords per acre.
In estimating tanbark in the Santa Cruz, Mendocino^and southern
Humboldt districts cruisers generally count 6 tree^to the. cord,
though sometimes the trees are so large that it takes 'only 4*ito pro-
duce a cord. In the northern Humboldt' district 8 or 9 trees /make
a cord and hi the Klamath 14. Cruisers are more likely to under-
estimate than to overestimate a claim. Exceptionally large trees
with thick bark produce from 2 to 3J cords of**bark. The figures
given in Table 2 are from trees on the inner edge of' the redwood belt.
TABLE 2. Amount of tanbark on oak trees of different sizes.
Diameter,
Height.
Length of
peeled
trunk.
Diameter
of peeled
trunk at
upper end.
Age.
Weight of bark.
Dry weight of
bark (calcu-
lated).
Inches.
Feet.
Feet.
Inches.
Years.
Pounds.
Pounds.
4- 9
30- 50
4- 8
3- 6
20- 40
15- 80
10- 70
10-12
40- 80
16-32
5- 8
40-100
80- 350
70- 250
13-18
80-100
32-65
7-12
70-125
350- 900
250- 650
19-24
90-120
65-80
7-11
100-159
900-1,700
650-1,200
24-36
115-140
80-95
9-11
125-180
1,700-2,500
1,200-1,800
36-48
100-120
80-90
9-18
350-210
2, 500-4, 000
1,800-2,800
48-60
100-120
80-90
9-18
170-250
3, 500-8, 000
2, 500-5, 700
To avoid discrepancies due to loose piling, the "cord" used in
selling tanbark is reckoned by weight rather than by dimension, and
is approximately a ton, though it varies in different localities from
2,200 to 2,600 pounds. It is most commonly 2,400 pounds, which is
the standard accepted in San Francisco. For bark that has been
peeled a year, 2,300 pounds is considered a ton. Very rarely a cord
is measured by dimensions; but where it is, as at Arcata, for instance,
it is 8 feet long, 4 feet wide, and 4| feet high.
PEELING.
The peeling season runs from about May 20 to about August 10,
but varies with latitude, weather, and locality. Peeling can be
started any time after the sap begins to run and continues during the
period of summer growth. Tanbark oak is extremely sensitive to
heat and cold as regards the adhesion of its bark. A cold spring
-delays the opening of the peeling season and a cool, moist summer
prolongs it. Trees on the shady north slopes will peel later than
those on the ridges or south slopes, but one of the periodic north
winds of the Coast Range, which are hot and dry, will make peeling
difficult or cause some trees to bind down completely. Cold nights,
on the one hand, will make the bark stick, and a hot period in July or
August will put an end to peeling. Trees standing side by side often
PRODUCTION OF TANBARK. 11
show different sensitiveness to weather changes; even two sides of a
tree may differ in ease of peeling and the north side stick before the
other.
Peeling is also affected by injury from fire, wind, or snowstorms.
Trees which are only slightly hurt by fire will not peel for two or three
seasons, and sometimes not at all. The wounds made when limbs are
broken off by windstorms or by the weight of snow have a similar
effect. Even the "try marks" on trees which are found not ready to
peel interfere with satisfactory work later in the season.
Peeling can be done more economically in the latter part of the
season because the bark, which is brittle in the early part, becomes
tougher then, so that it can be taken off in entire pieces.
At least half a day is required for two men to peel a large tree. The
peelers, therefore, never begin late in the day upon a tree which they
must leave unfinished until the next morning, as the bark may " bind
down" overnight.
The peelers work in pairs. Usually they rely on the woodsman's
one-edged ax alone, as they believe that the advantages of a spud
do not equal the saving of time when the ax alone is used. With the
blade of his ax the peeler tries the bark to determine if it is loose,
and if it is he cuts two circles through the bark, one at the foot of the
trunk, the other 4 feet above. The bark is then slit longitudinally
and taken off in from one to four pieces. (PL III.) The circle of bark
thus removed is called a " rim" or a " coil." The first coil is removed
from the standing tree because it is easier to work when the tree is
erect and because it prevents the loss in chips at the base of the tree,
where the best bark is. In felling, the woodsman takes advantage
of the lay of the land, of down logs, and of gullies, in order that the
trunk may not lie flat on the ground and interfere with the removal
of the bark. Most tanbark oak trunks are badly fire-hollowed, which
makes it difficult to place them accurately. After the tree is down
the small branches are lopped/and interfering shrubs are brushed out.
One man then goes ahead "Hnging," or cutting through the bark
around the trunk; the second man follows, slits the bark, and removes
the coils. This process is continued up the trunk until the bark
becomes less than one-half inch thick. As the "coils" are taken off
they are laid on the ground with the inner or "flesh" side up, where,
as they become dry, they harden and curl up.
The average woodsman peels from 1 to 1J cords per day. Where
the stand consists of trees with straight, clear trunks standing on
ridges, an expert peeler can cut from 4 to 5 cords in a day. In the
case of very limby trees it is a general practice to take the bark off
only the clear portion of the trunk and abandon much of the remaining
bark even where it is thick. The quality of such waste is shown by
the analyses given in Table 3.
12
CALIFORNIA TANBARK OAK.
TABLE 3. Analyses of bark wasted in abandoned tops.
Origin of samples.
Solids soluble in cold water.
Solids
soluble
in hot
water
only,
reds.
Total
solids.
Tannin.
Non-
tannin.
Total.
1. Sample taken 3 feet beyond last coil removed by
peelers
Per cent.
17.29
15.64
Per cent.
13.08
11.82
Per cent.
30.37
27.46
Per cent.
Per cent.
30.32
27.56
2. Sample taken 8 feet beyond last coil removed by
peelers
0.10
Although peeling into limby crowns adds disproportionately to the
expense because of the thinner bark and the extra trouble to get it,
nevertheless waste could be lessened economically through closer
supervision of the peelers.
It is customary to peel all the trees, even down to poles from 3 to 8
inches in diameter. One or two coils are taken from these poles
without felling them. This practice, called "jayhawking," also leads
to waste in bark. The two coils, which can be taken off without
cutting the tree down, do not always include all the bark worth
taking. In some districts " jayhawked" trees are frequent with clear
trunks for 20 feet above the last coil taken and bark three-quarters
of an inch thick. The quality of such waste is shown by the analyses
given in Table 4.
TABLE 4. Analyses of bark left on "jayhawked" trees, southern Humboldt County.
Description of tree.
Diame-
ter at 1
foot.
Total
height.
Solids soluble in cold water.
Solids
soluble
in hot
water
only,
reds.
Total
solids.
Tannin .
Non-
tannin.
Total.
1. Two co Us taken by peelers; sam-
ple from Just above second coil. .
2. One coil taken by peeler; sam-
ple from just above coil
Inches.
8
3.5
9
Feet.
50
25
55
Per cent.
13.05
13.85
10.12
Per cent.
6.71
7.15
6.72
Per cent.
19.76
21.00
16.84
Per cent.
0.09
.44
Per cent.
19.85
21.44
16.58
3. Two coils taken by peelers;
bark, sample from just above
TRANSPORTATION.
The bark curls up hi three weeks and is then tough enough to
stand handling. It is "bunched" or gathered together in small
regular piles. The swampers cut narrow sled roads through the
woods to the bunches of bark and it is sledded to the wagon road,
where it is corded up. In some districts the bark is carried out on
mule back, loaded on iron panniers.
After the bark is sledded a woodsman is sent through the woods to
sack the chips and search for bark which has been overlooked or
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE III.
**
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE IV.
FIQ. 1. PEELING 4-Foor RINGS OF BARK FROM THE FELLED TREE.
FIG. 2. BUNCHING THE BARK IN SMALL PILES ALONG THE SLED ROAD.
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE V.
FIG. L-THE SKIDWAYS TO WHICH THE BUNCHED BARK is SLEDDED, AND FROM WHICH
IT is HAULED TO THE RA/LROAD.
FlQ. 2.-HAULING THE BARK IN WAGONS FROM THE SKIDWAYS TO THE CARS.
PRODUCTION OF TANBARK.
13
covered up by the tops of the tress, but even with this precaution,
here and there bark piles are left whenever the peelings are extensive.
Chipped bark, which comes chiefly from the base or "rump" of the
tree, is the richest of all in tannin, and, on account of its greater weight
and smaller bulk than coil bark, particularly desirable. But it is
much more likely to be scattered and overlooked in the woods, and
it would be better woods practice if this bark were piled immediately
on peeling and sacked just before the coil bark is bunched. The cost
would be no greater than- in all probability not as much as by the
present method. The tannin quality of rump bark is shown in
Table 5:
TABLE 5. Analyses of the tannin quality of rump baric.
Locality.
Solids soluble in cold water.
Solids
soluble
in hot
water
only,
reds.
Total
solids.
Tannin.
Non-
tannin.
Total.
Southern Humboldt County
Per cent.
29.20
20.89
Per cent.
12.86
6.97
Per cent.
42.06
27.86
Per cent.
2.86
3.26
Per cent.
44.92
31.12
Santa Cruz County
On the Sonoma and Mendocino coasts the tanbark is usually trans-
ported to the ocean by the steam logging railways, which follow the
courses of the numerous rivers and creeks. These roads were built
primarily to carry redwood, but have cars with frames for tanbark.
The Mendocino coast is rockbound and there are no real harbors, but
only open roadsteads or half-sheltered coves. The cars are run out
upon a headland, and the frame, with its load, is lifted by a steam
derrick and transported by a cable to a schooner offshore. A schooner
that carries 200 cords of bark may be loaded thus in a very short time.
Nearly all of the bark shipped by schooner from the Mendocino coast
goes to the San Francisco Bay tanneries.
Sometimes tanbark is transported to the coast by four-horse wagons,
which have a capacity of from 2 to 4 tons.
The bark delivered for shipment must be air-dry and, according to
the rules, must not include any "paper bark" or "snake skin" that
is, bark less than half an inch thick. In practice, however, thin bark
is included in the shipments without arousing protest, provided there
is not too much of it. In the hot, rainless summers of the Coast Range
there is no difficulty in meeting the requirement that the bark be
air-dry. Bark rarely reaches the market in less than from four to
eight weeks from the tune of peeling. Heavy bark loses from 25 to
30 per cent of water in this period, medium bark from 30 to 35 per
cent, second growth and paper bark from 35 to 40 per cent. There
is also a slight loss, from 0.5 to 1 per cent, due to breakage in han-
dling and shipping.
14
CALIFORNIA TANBARK OAK.
The long dry season of California is highly favorable to the tanbark
industry , since it obviates precaution against rain. Bark held over
winter must be sheltered, since more than 25 per cent of tannin is
leached out by rain in one winter. Dampness also causes mold,
which injures the leather and is difficult to get rid of.
QUALITY OF THE BARK.
The proportion of tannin varies with the part of the tree from which
the bark is taken and with the local and geographical situation of the
tree. Old bark near the base of the trunk contains the highest pro-
portion. The color of a cross section of fresh bark is an index of the
quality in this respect ; bark richest in tannin is a deep red, while the
poorest is pale or yellowish. Bark is not considered ripe until it has
formed three layers, a rougher outer "ross," a central "meat," and
an inner "fiber." Before it has divided thus the tannin content is
low. Trees in virgin stands arrive at this maturity at from 55 to 70
years of age.
The variation in bark quality on a typical tree is shown in Table 6 :
TABLE 6. Analyses showing distribution of tannin from the base to the top of the tree. 1
Location of sample.
Thick-
ness of
bark.
Solids soluble in cold
water.
Solids
soluble
in hot
water
only,
reds.
Total
solids.
Tan-
nin.
Non-
tannin.
Total.
Rump
Incht
li
1
1
1
i
i
5.
>,
s,
Per ct.
29.20
25.77
19.93
16.13
19.37
13.16
13.21
10.00
12.50
10.82
Per ct.
12.86
12.72
10.76
9.26
11.63
9.40
8.17
6.78
9.42
8.42
Per ct.
42.06
38.49
30.69
25.39
31.00
22.56
21.38
16.78
21.92
19.24
Per ct.
2.86
Per ct.
44.92
38.49
30.69
25.39
31.16
22.56
21.38
16.78
21.92
19.24
First "cut
15 feet
31 feet
45 feet
0.16
60 feet
66 feet.
74 feet
78 feet..
84 feet
1 Tree 18 inches in diameter 4 feet from the ground, and 96 feet high, in northerly h'ollow, southern Hum-
boldt County.
Sunshine and light increase the secretion of tannin. For this
reason the best bark grows on ridges, and the southern districts yield
a richer product than the northern. Bark from the Santa Lucia
Mountains, the southernmost of all the districts, is the richest in the
market and averages as high as from 20 to 24 per cent. According
to the tanners who have used bark from widely separated districts,
that grown in the "Bald Hills" district in the interior, beyond the
influence of the sea fogs, is richer than that from the coast, where the
trees are shaded by redwoods and are in the fog belt. Bark from the
coast of Oregon is low in tannin, with an average of only 12 or 14
per cent.
PROLONGING THE SUPPLY.
15
Table 7 shows the results of analyses of bark of representative trees
of the various districts:
TABLE 7. Analyses of bark samples from different districts.
Bald Hills districts.
Solids soluble in cold water.
Solids
soluble in
hot water
only,
reds.
Total
solids
extract.
Tannin.
Nontan-
nin.
Total.
Thick bark, commercial sample, Briceland, Hum-
boldt County
Per cent.
24.74
14.82
14.90
15.66
15.36
20.51
22.20
14.92
14.00
16.20
22.73
19.08
21.61
18.93
18.24
Per cent.
13.18
9.60
11.86
7.12
10.02
11.21
11.69
8.89
6.73
8.92
10.07
9.76
6.85
5.40
9.24
Per cent.
37.92
24.42
26.76
22.72
25.38
31.72
33.89
23.81
20.73
25. 12
33.80
28.84
28.46
24.33
27.48
Per cent.
3.08
1.78
2.16
2.52
1.88
3.24
2.87
1.15
1.86
3.76
1.14
7.96
2.14
2.67
3.60
Per cent.
41.00
26.20
28.92
25.24
27. 26
34.96
36. 76
24.96
22.59
28.88
34.94
36.80
30.60
27.00
30.08
Thick bark, Acorn region, llumboldt County
Thin tfark, Acorn region, llumboldt County
Between Low Gap and Summit, west of Ukiah:
It-foot tree, sample at 3 feet from ground, ridge
tree
ly-foot tree within 15 feet of preceding
Just east of Coast Range summit (west of Ukiah);
Elk Creek, Mendocino County:
Thick bark >
Medium bark .
Thin bark
Ridge tree in open, near coast at Kenny's; 2-foot tree.
Ridge tree near coast at Kenny's' 2-foot tree
South slope tree exposed to sun, Halfway House,
Ukiah-Mendocino Road; 2-foot tree
San Vicente Creek, Santa Cruz Mountains, Redwood
district:
3-foot smooth-barked tree
Rough-barked tree within 10 feet of preceding;
2i-foot tree
San Vicente Creek, Santa Cruz Mountains, S.Woot
tree
PROLONGING THE SUPPLY.
With the disappearance of the bodies of tanbark oak which have
furnished the chief tanning material for the leather manufacturing
industry on the Pacific coast the question of the continuation of the
supply becomes very important. Since the greater portion of the
standing tanbark is now confined to broken and inaccessible moun-
tain country, the extension of transportation facilities to those
regions must exert a very marked influence on its exploitation and
cost. Railroads and wagon trails are being rapidly pushed into the
northern coast ranges, and it is probable that within two or three
years the rich belts of Mendocino, Humboldt, and Del Norte Counties
will have at least one railway line. The utilization of second growth;
the introduction of more conservative methods in the woods, par-
ticularly in connection with the redwood lumbering industry; the
protection of the forests from fire; and the extension of the use of
other products as substitutes for and supplements of the bark of
this most important tree, will all have their influences on the future
supply.
16 CALIFORNIA TANBARK OAK.
PROVIDING FOR SECOND GROWTH.
SPROUT REPRODUCTION.
For the maintenance of the supply of tanbark on the Pacific coast
the second growth on cut-over areas offers by far the most hope.
Sprout reproduction must be encouraged, since the tree sprouts very
readily and with great persistence. Sprouts grow from trees of prac-
tically Siuy age and under a wide variety of conditions. Of greatest
economic significance are those which spring up from the stumps of
trees felled for peeling. The sprouts arise from conical woody buds
which are formed under the bark at the base of the tree, and which
vary in number from a scattering few to crowded thousands. The
sprouts themselves vary in number; as many as 1,400 have been
counted on one large stump. The practice of peeling the tree down
as far as possible, often below ground level, in order to obtain all the
rich and heavy rump bark, exposes the buds and prevents sprouts,
but peeling can safely be carried down to the surface of the ground
if the peelers ring the bottom of the first run instead of stripping off
the bark as far down as it can be torn. The original number of
sprouts is reduced by natural processes in 30 years to from four to
eight of the most vigorous poles. The rate of height growth is about
2 feet a year. By proper thinning this rate could be accelerated.
Sprouts also come up freely about the base of fire-injured and even
fire-killed trees, which is a great advantage where there are frequent
forest fires, as in the tanbark oak regions. They even grow vigor-
ously from the stumps of old trees which have been weakened by
dry rot or fire and have fallen. The Stumps of such fallen veterans
may be a yard or two in diameter. Circles of sprouts about the rims
of such stumps which have disappeared are often found in the woods,
and the trunks of these sprouts are sometimes 2 feet in diameter at
4 feet from the ground. Sometimes sprouts will start from the base
of living trees, though this habit is of slight commercial importance.
Nothing can better illustrate the vitality of tanbark oak than the
longevity of standing trees which have been peeled. Peeling is
usually done before flowering time, and for the first year afterwards
the growth of the tree is so decidedly checked that it does not fruit.
The second year the tree bears a full crop of acorns often an exces-
sively large crop. The woodsmen call this the "last kick" of the
tree, since in the third year it usually dies. If the tree stands exposed
to the full heat of the sun it will probably die the first season. Yet
there is abundant testimony that it may continue to live for a long
period even 10 or 15 years. The apparent anomaly of a tree con-
tinuing its life functions with a complete band of bark removed from
its trunk can be explained by a study of "jayhawked" trees in the
field. Such trees were peeled either so early in the season or so late
PROLONGING THE SUPPLY. 17
in the season that the bark did not part readily from the wood, and
a very thin portion of the inner bark and cambium layer adhered to
the wood and formed a sort of film. This film after one season looks
like a thin ooat of brown varnish. The wood beneath, however, is
greenish and pulpy, suggesting the mesophyll layer of a leaf. This
layer does not increase appreciably in thickness.
REPRODUCTION BY SEED.
No other oak on the Pacific coast produces so heavy a crop of
acorns as tanbark oak, but seedlings, nevertheless, are not abundant.
In the main, forest seedlings are found only where a fallen tree has
made a break in the forest canopy and let in light. The "Bald
Hills" country is filled with hogs and cattle, which prevent seedling
reproduction by devouring the acorns and browsing the tender foli-
age of the young growth.
Attempts at artificial . propagation outside the natural range of
tanbark oak have failed. The acorns germinate in open nursery beds
in about five weeks. The seedlings come up a little more promptly
in loam beds than in adobe, but those in the adobe seem a trifle more
vigorous than the others. Sand beds germinate only 2 per cent of the
Eighty per cent of the seeds planted in 1902 at the California For-
estry Station at Chico germinated, but not one seedling survived the
first summer, although the soil conditions are favorable. The hot,
dry climate of the interior valleys does not furnish a normal environ-
ment for tanbark oak, and the formation of plantations is practica-
ble only where conditions are similar to those of the natural range
of the tre*e.
SECOND-GROWTH BARK.
For several years second growth has been peeled in the Santa Cruz
Mountains, and it is claimed by some owners who superintended both
peelings that the yield of second growth exceeds that of the virgin
stand. There is nothing to prove or disprove this assertion, but it
is probable that these men did not take account of the fact that the
harvesting of the crop to-day is very much closer and more careful
than the peeling of the virgin timber from 30 to 50 years ago, and
that "passed trees" of the virgin stand were stripped at the sec-
ond peeling. Although it is improbable that the yield of second
growth at the end of 30 years would equal that of the original
stand, it is sufficiently heavy to make the holding of cut-over lands
profitable for repeeling in 30 years, when from 1 to 5 cords per
acre can be harvested.
Table 8 gives the yields of a number of second-growth trees in the
Santa Cruz Mountains.
89446 Bull. 7511 3
18
CALIFORNIA TANBARK OAK.
TABLE 8. Amount of bark on second-growth tan oak, age 29 to 31 years, Santa Cruz
Mountains.
Height
of tree.
Diame-
ter of
trunk at
2 feet.
Length
of peeled
trunk.
Diame-
ter of
trunk at
end of
last coil.
Thick-
ness of
bark at
butt.
Weight
of bark,
green.
Weight
of bark
dry (cal-
culated).
Feet.
Inches.
Feet.
Inches.
Inches.
Pounds.
Pounds.
52
7
24
4
U
145
91
50
6
24
4
1J
143
90
62
10
24
6
li
241
152
55
7
20
4
I*
125
79
65
9
28 ,
6
2
. 243
152
55
7
20
, 5
11
120
76
62
8
- 24
5
l|
158
100
62
7
24
5
I*
160
101
60
8
28
6
2
235
148
65
10
28
6
i
303
191
70
9
28
6
i
303
191
67
10
36
5
2"
321
202
68
9
36
5
|
241
152
67
9
32
5
{
208
131
65
8
32
5
177
112
QUALITY OF SECOND-GROWTH BARK.
Tanners estimate that second-growth bark will average only 10 per
cent tannin, and when it was first put upon the market they objected
to it; but, mixed with virgin bark, it is now used to a considerable
extent. It is distinguishable from virgin bark by its peculiar smooth-
ness both on the outside and the inside; by its brittleness, due to lack
of fiber, especially toward the inside, where virgin bark is so fibrous;
and by its sappiness and light color.
Table 9 shows the characteristics of samples taken from near the
bases of trees. The thinner bark higher Up would, of course, lower
the average.
It is possible to produce a good quality of leather by tlie use of
second-growth bark alone, but a large quantity is required to offset
its low tannin content. The item of labor is also greater, since it costs
more to handle the extra bark.
TABLE 9. Analyses showing tannin content of tan-oak bark taken from thr& 'Second-
growth trees.
Locality.
Height.
Diame-
ter of
wood at
1 foot.
Age.
Solids soluble in cold water.
Solids sol-
uble in
hot water
only,
reds.
Total
solids.
Tannin.
Nontan-
nin.
Total.
Between Comptche
and Low Gap, one of
16 sprouts about
stump
Feet.
Mi
'40
60
Inches.
2*
5
9
Years.
7
24
30
Per cent.
18.28
16.22
14.10
Per cent.
8.28
10.60
8.94
Per cent.
26.56
26.82
23.04
Per cent.
1.00
, -56
.52
Per cent.
27.56
27.38
23.56
Between Comptche
and Low Gap
San Vicente Creek,
Santa Cruz Moun-
tains
PROLONGING THE SUPPLY. 19
CONSERVATIVE METHODS IN THE WOODS.
Redwood lumbering has done much to keep the annual supply of
tanbark steady and to make remote stands accessible. It is the
practice of the redwood lumber companies to send tanbark crews
through the woods in advance of the redwood logging crews, since the
firing of the district, which always follows felling, to facilitate the get-
ting out of the redwood logs by wire cable and donkey engine, badly
injures all standing trees, and even if it does not actually destroy the
tanbark oak it makes peeling .difficult or impossible.
GUARDING AGAINST FIRE.
Up to the present time no attention has been paid to the future
condition of the forestf in which peeling has been carried on. Yet the
introduction of conservative methods would prevent a very large
waste. Fire, which always accompanies redwood logging, makes it
an economical policy to take all the bark possible, whether the .tree
has reached maturity or not. Under conservative methods " jay-
Hawked" trees, which yield only from 10 to 60 pounds of bark with
a low tannin content, would in 10 or 20 years form profitable elements
in the new stand for both bark and wood. Despite the custom of
taking all the bark that can be peeled without regard to whether it
is mature or not, the maximum yield is never obtained under present
methods. Some trees which will not for one reason or another peel
readily in one season, although they would a year or two later, are
sacrificed in order to chip a little bark off their trunks or to secure one
or more coils because the trees are considered as doomed to fire any-
way. Often from 70 to 90 per cent of the bark in such cases can not
be taken from the tree. Moreover, the fires kill very young trees, kill
sprouts down to the stumps, and seriously interfere with reproduction.
Under conservative management the older trees would be saved for
peeling in a favorable year and the younger ones permitted to develop
a new stand. As tanbark oak always grows in mixed stands, the
holding of redwood and Douglas fir lands for a second crop would
give the tanbark oak the necessary fire protection and would furnish
a profitable element in the later harvests.
During the rainless season in California, from May to October, even
in the foggy coast region, fires caused by logging crews, hunters,
campers, and in the far north coast ranges by thunderstorms, lead to
several million dollars damage every year. These fires rarely kill tan-
bark oak trees, but make long vertical wounds from 4 to 10 feet up
the sides of the trunks. On young trees these injuries are often com-
pletely covered by the meeting of new bark growth, but with trees
more than 100 years old the sides of the' wound usually spread. The
exposed wood rots, andsucli trees, called " goose pens," are difficult
20 CALIFORNIA TANBARK OAK.
to lay out accurately in felling. Even a slight injury to the trunk
permits the entrance of fungi which weaken the wood, and the loss of
such trees in heavy snowfalls is very large.
Trees on slopes or canyon sides are the greatest sufferers; 95 per
cent of the tanbark oak trees in those positions are injured by fire
and 80 per cent fire hollowed. In the case of ridge trees, about 80
per cent are comparatively free from fire hollows, because a fire
traveling up a slope is either running high or going out when it
reaches the top.
The most extensive destruction by fire in the tanbark oak belt
has probably been in Del Norte County, where in former days the
Indians regularly fired the woods to make better feed for the deer,
and the packers set fires to keep the trails open. Kidge after ridge
has been wholly or partly reduced to a low chaparral growth, although
there is evidence that a dense forest existed at a comparatively recent
date. A conservative estimate of the loss of tanbark by fire within
15 years in this region is 60,000 cords.
In the second-growth districts the accumulation of debris inside
the circles of poles about the remains of the parent stumps furnishes
material for flames. Forty per cent of such poles show serious injury
at the bases.
("^TANNIN EXTRACT PROCESSES.
.The difficulty of transportation has prevented the exploitation of
some of the most productive tanbark oak regions in Humboldt and,
to a smaller extent, in Mendocino County. An attempt was made
to reduce this difficulty by grinding up the bark and shipping it in
sacks, but this did not help in the more remote districts where the
weight was the chief drawback. In the last few years attempts
have been made to solve this difficulty by extracting the tannin
from the bark and shipping the extract.
Two methods have been tried in California, the open-pan process
and the vacuum-pan process. The open-pan process was tried in
southern Mendocino County hi 1900 and 1902, but was abandoned
because the heat necessary to secure rapid evaporation in concen-
trating the mixture of ground bark and liquid was said to scorch
the fluid and start fermentation, so that the barrels containing the
completed product often burst.
The vacuum-pan process is used by an extract plant at Briceland,
Humboldt County. The liquid from the leaching vats is pumped
into settling tanks in the concentrator house, and thence fed as
needed into the "pan" or evaporator, which is a copper retort about
7 feet in diameter, heated by steam pipes coiled around the base.
By heating the pan under vacuum the temperature of the liquid
during evaporation is kept from exceeding* about 120 or 130 F.
TANNIN EXTRACT PROCESSES. 21
The vapor is condensed in a receptacle high enough above the pan
to permit a 34-foot vertical waste pipe. This pipe, kept full of water,
supplies a water column sufficient to offset the atmospheric pressure
and maintain the vacuum.
A cord of dry bark, 2,200 pounds, is reduced to 50 gallons of
extract, which weighs about 550 pounds. The extractor has a
capacity of 12 cords a day.
SUPPLEMENTAL MATERIALS.
The duration of the bark supply from tanbark oak will be extended
somewhat by the use of other materials as supplements or substi-
tutes. The superiority of the product of the tanbark oak over all
other Pacific coast barks is due not altogether to its high percentage
of tannin, but rather to the quality of the particular tannin con-
tained in it, and perhaps also to the presence of certain other acids,
such as gallic and acetic. The value of this combination is proved
by tanning experience. Mixing imported tanning materials, such
as gambier and quebracho, increases its effectiveness and counter-
acts some of its undesirable qualities. As tanners have learned the
use and value of these supplementary agents, methods have been
more and more adapted to them, until to-day they are regarded as
indispensable and the tanbark oak product is never used alone.
As the accessible supply of tanbark oak grows scarcer and dearer,
the bark from other species of oak is occasionally mixed with the
superior material. This is especially the case in the southern dis-
tricts, where the tanbark oak is more nearly exhausted. The barks of
the California black oak and the coast live oak run so high in tannin
that if tannin content alone were an index of tannage value they
could compete with tanbark oak. They can not be used alone,
because they will not produce leather of goo'd quality; the live-oak
bark in particular imparts a gritty character to the leather, which
ruins the knives of the cutters, but mixed in moderate quantities
with the better bark they make possible a considerable saving.
Alder bark is occasionally found in shipments of bark from tan-
bark oak, but the tree does not grow in sufficient quantity in Cali-
fornia to be a factor in bark supply. In the Mendocino woods the
chinquapin is often peeled, but it contains so little tannin that it is
practically worthless. Moreover, it is very fibrous and tough, which
makes it difficult for the smaller tanbark mills to handle.
Analyses of average bark samples from the main trunks of the
important California trees are given in Table 10. Some of these
have never been subjected to commercial experiment.
22 CALIFORNIA TANBARK OAK.
TABLE 10. Tannin analyses of bark of the more important forest trees of the Pacific coast.
Species.
Locality.
Soluble solids.
Insoluble
solids,
reds.
Total
solids.
Tannin.
Xontan-
nin.
Total.
California black oak (Quer-
cus calif or nica).
California black oak
Vaca Mountains, So-
lano County.
Briceland, Humboldt
County.
Berkeley
Per cent.
10.00
10.16
18.76
7.92
6.67
12.18
6.56
11.97
7.07
6.20
7.60
8.60
1.45
15.58
14.11
13.45
9.03
17.52
7.15
10.80
14.40
2.50
1.76
3.91
Per cent.
10.25
7.88
9.40
5.88
2.83
10.18
5.19
11.28
4.93
4.16
4.34
12.00
3.09
10.46
2.85
3.99
4.59
6.24
5.25
3.46
6.56
2.74
5.72
5.85
Per cent.
20.25
18.04
28.16
13.80
9.50
22.36
11.66
23.25
12.00
10.36
11.94
20.60
4.54
26.04
16.96
17.44
13.62
23.76
12.40
14.26
20.96
5.24
6.48
7.76
Per cent.
0.95
.32
1.48
1.20
1.64
.80
1.00
1.55
.36
1.00
.64
1.68
.00
.97
2.60
3.72
.74
1.60
.42
1.32
2.42
.10
.59
1.58
Per cent.
21.20
18.36
29.64
15.00
11.14
23.16
12.66
24.80
12.36
11.30
12. 08
22. 28
4.54
27. Gl
19. 50
21. 16
1^.36
25. 36
12. 82
15.58
23.38
5.34
7.07
9.34
California live oak (Quercus
agrifolia).
Highland oak (Quercus wis-
lizeni).
Highland oak
Vaca Mountains, So-
lano County.
Southern Mendocino. .
Vaca Mountains, So-
lano County.
South central Mendo-
cino.
Visalia
Canyon live oak, maul oak
(Quercus chrysolepis).
Canyon live oak
California white oak (Quer-
cus lobata).
Pacific post oak (Quercus
garryana).
Pacific post oak
Southern Humboldt . .
South central Mendo-
cino, "Bald Hills."
Southern Humboldt . .
Mendocino coast .
Western chinquapin (Cast-
anopsis chrysophylla).
Red alder (Alnu-s oregona)...
California yellow willow;
western black willow
(Salix lasiandra).
California laurel ( Umbel-
lularia californica).
Monterey pine (Pinus radi-
ata).
California swamp pine
(Pinus muricata).
Lowland fir (Abies grandis)
Berkeley
Briceland
Berkeley (cult.)
Mendocino coast
...do
Sitka spruce (Picea sitchen-
sis).
Douglas fir (Pseudotsuga
taiifolia).
Western hemlock ( Tsuga
heterophylla).
Western hemlock
do
Southern Humboldt . .
Mendocino coast
Noyo River, Mendo-
cino coast.
Mendocino coast
do
Redwood (Sequoia semper-
virens) bark.
Redwood, sapwood
Redwood, heartwood
do
POSSIBILITIES OF UTILIZING THE WOOD.
The tanbark oak peeled since 1850 is equal to more than 2,000,000
cords of firewood. But, chiefly on account of the difficulty of trans-
portation, little of this amount, perhaps 5 per cent, has been used as
fuel. Yet the wood has such particular value for special purposes
that it is quoted in San Francisco at from $12 to $18 per cord, a price
much higher than that of any other California oak. The wood burns
up very completely with little smoke. The United States mint
at San Francisco uses it, and there is a steady demand by the bakers
of that city. The full possibilities of the wood for lumber can be deter-
mined only by experiments in sawing and seasoning and by strength
tests, but its availability for some purposes is undoubted. About
400,000,000 feet have been utterly lost so far, and about 627,000,000
feet are still standing. To utilize the log for lumber, it must be cared
for immediately after peeling. Only the redwood logging companies
possess facilities for yarding and sawing the tanbark oak; yet since the
peeling time comes at the height of their busy season, any proposal
CONCLUSIONS. 23
to depart from the custom of abandoning the tanbark oak log as use-
less does not meet with favor. Moreover, their milling machinery
is not well adapted to sawing oak logs, and, for satisfactory work,
the installation of special plants would be necessary.
Country wagon makers in the Coast Range constantly use tanbark
oak for repair work and believe it superior to all other wood for felloes.
The wood, unlike some others, such as the eastern chestnut, has no
value whatever as a tanning agent.
CONCLUSIONS.
(1) The bark of tanbark oak is one of the most valuable tanning
agents known for the production of heavy leather. Bark from the
interior ridges and southern districts is prized more than bark from
the deep redwood belt or from northern districts, because it averages
higher in tannin.
(2) The Pacific coast tanbark-oak belt contains enough standing
tanbark at the present time to supply the needs of California tanneries
at their present rate of consumption for 47 years.
(3) There should be more systematic methods in peeling and a
greater proportion of the bark above the clear trunk should be taken.
Bark from one-half to one-fourth inch thick ^should be saved when-
ever possible. Chipped bark should be sacked before bunching the
coil bark. Trees with bound bark should be temporarily passed,
and not mutilated or sacrificed. Tops should be burned in the win-
ter following cutting to prevent the destruction of young growth and
of passed trees by wild forest fires.
(4) Tanbark oak is surpassed in reproductive powers by no
other forest trees in western America, except the redwood, and it
stands very close to that species. A crop of sprouts will normally
arise from the base of every peeled stump. In order to favor this
crop, peelers should ring the trunk at base and not break the coil
down below the surface of the ground. These sprouts will give rise
to " second-growth" poles which are commercailly profitable to peel
within 25 or 35 years.
(5) Standing trees after being peeled may live on indefinitely, but
they never produce a second bark which has any commercial value.
(6) The wood is, for the most part, allowed to rot on the ground.
Prompt care would tend to obviate its greatest weakness, checking
in seasoning, and it can certainly be applied to some of the uses for
which oak wood is prized, and a stupendous annual waste thereby be
eliminated.
(7) Forest fires are a source of great annual loss, and. cooperative
measures should be taken by the State of California, the coast counties,
the redwood companies, the tanbark companies, and cattle-range
owners to reduce the danger from fire. A conservative treatment
of the redwoods to obtain a continuous crop will be of like advantage
to the tanbark oak mixed with it.
PART II. UTILIZATION OF THE WOOD OF TANBARK OAK,
By H. S. BETTS.
TANBARK-OAK LUMBER, v
While the wood of tanbark oak is sometimes used for fuel, it is
more generally burned in the redwood logging operations, or left to
rot in the woods. The object of this study is to bring to the atten-
tion of west coast hardwood users and the owners of tanbark-oak
stumpage the possibility of using tanbark-oak lumber.
The largest part of the hardwoods used on the Pacific coast is
imported from the eastern part of the United States. From 1899 to
1906 there was an increase in the price of hardwoods in the East of
from 25 to 65 per cent. These conditions have been reflected in the
western hardwood markets. Not only are the prices of most kinds
of hardwood going up rapidly, but in some cases certain species are
difficult to obtain at any price. This scarcity is due not to any local
condition, but to the general shortage of hardwood timber. The
high price is due to the eastern market price, to which must be added
about 85 cents per hundredweight in freight charges, or an advance
of from $24 to $36 or even $40 per thousand board feet.
Yet tanbark oak furnishes a fair quantity of good material. For
instance,, the average yield of bark is from 1J to 2^ cords per acre.
If, as seems reasonable, there are 800 feet board measure of lumber
for every cord of bark, the yield in lumber would be from 1,000 to
1,760 feet board measure per acre. Exceptionally fine stands yield
as high as 8 cords of bark to the acre, which would mean 6,400 board
feet of lumber.
APPEARANCE AND CHARACTERISTICS OF THE WOOD.
The wood of tanbark oak, like that of other oaks, is porous and
has the characteristic strongly marked medullary rays. In color it
is light brown, faintly tinged with red. When the wood is first cut
the sap wood is somewhat lighter in color than the heartwood, but
after a few weeks' exposure to the air the two become very similar
in appearance.
Exact knowledge of the rate of growth of tanbark oak is very
limited. Seven forest-grown trees near Sherwood, Cal., showed varia-
tions of from 10 to 20 rings per inch. The trees were from 14 to 27
inches in diameter 2 feet above the ground. Even on the stump the
24
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE VI.
FIG. 1. MACHINE AND METHOD USED FOR TESTING SMALL BEAMS.
FIG. 2. SEASONING CHECKS IN THE BUTT OF A TANBARK OAK LOG THAT HAS BEEN
SUBJECTED TO THE SEVERE TEST OF BEING TURNED UP AND EXPOSED TO THE HOT
CALIFORNIA SUN FOR Six WEEKS.
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE VII.
FIG. 1. TANBARK OAK LUMBER FOR CAR CONSTRUCTION.
FIG. 2. TANBARK OAK BOARDS AIR DRYING.
APPEARANCE AND CHARACTERISTICS.
25
annual rings are difficult to distinguish, since the temperature changes
from season to season are not marked enough to form the distinct
bands of spring and summer wood common in eastern oaks. In the
case of the lumber, it becomes impracticable to attempt to obtain the
rate of growth of different pieces.
STRENGTH.
The material used in the tanbark oak tests was divided into three
classes or shipments, differing in the age of the trees and the season
of cutting. The first two shipments were selected in the summer
during the peeling season, and represented in the first shipment the
larger and more mature trees of the stand, and in the second shipment
the smaller and younger trees. The third shipment was felled in
October and represented the same wood as that obtained in the first
shipment, but felled in the season when the bark was tight, or when
the sap was not running.
The strength of the wood in several conditions of seasoning is
shown in Table 11. The three shipments had practically the same
strength and, therefore, were combined in the table.
TABLE 11. Strength of small clear pieces of tanbark oak, green, air-dry, and kiln-dry,
size 2 by 2 inches in section.
GREEN.
Bending.
Num-
ber of
tests.
Mois-
ture
con-
tent.
Weight per
cubic foot.
Fiber
stress at
elastic
limit
per
square
inch.
Modu-
lus of
rupture
per
square
inch.
Modu-
lus of
elastic-
ity per
square
inch.
Elastic
resil-
ience
per
cubic
inch.
As
tested.
Oven
dry. i
Average
256
26
26
Per ct.
89.5
110.5
65.5
Pounds.
66.5
71.7
60.3
Pounds.
43.1
48.1
38.2
Pounds.
6,576
8,283
4,869
Pounds.
10, 707
12,880
8,632
1,000
pounds.
1,678
2,251
1,203
Inch
pounds.
1.49
2.35
.83
High 10 per cent
Low 10 per cent
AIR-DRY (10 TO 20 PER CENT MOISTURE).
Average
567
14.0
45.2
43.2
9,080
15, 512
2,083
2.27
High 10 per cent
57
17.4
51.7
50.5
11,901
20,342
2,771
3.45
Low 10 per cent
57
10.5
39.5
37.1
6,482
11,625
1,511
1.19
KILN-DRY (5 TO 10 PER CENT MOISTURE).
Average
31
9.6
45.4
43.9
9,289
17,693
2,292
2.17
High 10 per cent
3
' 10.0
50.2
48.8
12,287
22, 417
2,966
3.41
Low 10 per cent
3
8.8
40.9
39.5
6,600
13, 077
1,642
1.11
26
CALIFORNIA TANBARK OAK.
TABLE 11. Strength of small dear pieces of tanbark oak, green, air-dry, and kiln-dry,
size 2 by 2 inches in section Continued.
GREEN.
Compression parallel to
grain.
Compression perpendic-
ular to grain.
Shearing.
Num-
ber of
tests.
Mois-
ture
con-
tent.
Crushing
strength
per
square
inch.
Num-
ber of
tests.
Mois-
ture
con-
tent.
Strength
at elastic
limit, per
square
inch.
Num-
ber of
tests.
Mois-
ture
con-
tent.
Strength
parallel
to grain
per
square
" inch.
Average
237
24
24
Per ct.
86.8
105.4
64.8
Pounds.
4.845
5,819
3,711
244
24
24
Per ct.
77.9
95.3
59.7
Pounds.
1,355
1,964
926
221
22
22
Per ct.
83.1
103..
56.1
Pounds.
1,414
1,685
1.075
High 10 percent. .
Low 10 per cent
AIR-DRY (10 TO 20 PER CENT MOISTURE).
Average
406
14.4
8,172
316
13 4
1 656
204
13 3
1 %0
High 10 per cent
41
17 7
10 405
32
16 9
2 343
20
16 9
2 402
Low 10 per cent
41
10.7
6,265
32
10 5
1 238
20
10 6
1 585
KILN-DRY (5 TO 10 PER CENT MOISTURE).
Average *
28
9.4
9,398
26
9 5
1 818
22
9
2 037
High 10 per cent
3
10
10 737
3
10
2 293
2
10
2 384
Low 10 per cent. .
3
8.2
8,047
3
8 4
l'366
2
7 3
1 669
1 The values in this column are based on a shrinkage of 18 per cent volume. The fiber saturation point
is taken as 30 per cent moisture.
Clear, straight-grained specimens free from defects are needed in
determining the strength of the wood itself. The results of tests
made on this class material can also be used for comparison with
similar tests on other kinds of wood. Pieces 2 by 2 inches in section
have been found weh 1 suited to tests of this kind. For bending, 1
they are cut about 30 inches long, and for compression parallel to
the grain and compression perpendicular to the grain, from 6 to 10
inches long. The blocks for shear parallel to the grain are cut with
a projecting lip that is sheared off under test. In making a bending
test the beam is supported at the ends and loaded at the middle.
The supports for the beam are on the weighing platform of the test-
ing machine, so that the load on the beam can be determined at any
time during the test. This load is applied by a crosshead which
can be forced down on the test specimen by means of heavy screws
turned by a train of gears. The deflection or bending of the beam is
measured by an apparatus (PL VIII, fig. 1 ) consisting of a light steel
frame on which is mounted a movable pointer. In making a test,
the frame is rested on two nails driven into the beam near the ends
and the pointer attached to the center of the beam in such a way
1 For a detailed description of methods used in the tests, see Forest Service Circular 38 (revised), Instruc-
tions to Engineers of Timber Tests.
APPEARANCE AND CHARACTERISTICS. 27
that it moves over a graduated arc when the beam bends, and thus
shows the amount of bending.
The test is begun by loading the beam with about one-twentieth
of the probable breaking load and noting the deflection. The load is
then increased by a certain increment which is recorded with the cor-
responding deflection, and the process continued until the beam breaks.
The results of tests on beams of various sizes are reduced to a unit
basis, so that direct comparisons as to strength and stiffness can be
made between pieces of different sizes of the same or of different
species of wood.
In computing the results, the breaking strength is represented by
11 modulus of rupture," the stiffness by " modulus of elasticity," the
load the material will carry without taking a set by " fiber stress at
the elastic limit," and the ability to withstand shock without taking
a set by " elastic resilience."
Tests in compression parallel with the grain are made by crushing
the specimens endwise as they stand upright on the platform of the
testing machine. In the case of compression perpendicular to the
grain, the tests are made by placing a piece of metal 2 inches wide
across the test specimen as it lies flat on the platform of the machine
and pressing the piece of metal against the block of wood by means
of the crosshead of the machine. This test is carried only slightly
beyond the elastic limit of the wood under test, as loading beyond
that point has at present no significance. The action is similar to
that of a rail on a tie.
In making a shearing test the block is clamped firmly in a frame
with the lip projecting. The frame is placed on the platform of the
machine and the lip sheared off by means of a sliding plate applied
against the upper surface of the lip and parallel to the gram.
Table 1 1 shows the oven-dry weight of tanbark oak to be about
43.2 pounds per cubic foot. Air-dry tanbark oak, containing 15 per
cent moisture, weighs about 50 pounds per cubic foot, or 4,160
pounds per 1,000 board feet. This weight is about- the same as that
of white oak and is somewhat higher than that of red oak.
The average bending strength (modulus of rupture) of green tan-
bark oak is 10,707 pounds per square inch, and the average crushing
strength, 4,845 pounds per square inch. The results of similar tests
on several kinds of hickory by the Forest Service, including pignut,
shagbark, mockernut, big shellbark, nutmeg, and water hickory
show a bending strength of from 9,200 pounds per square inch for
green nutmeg hickory to 11,450 pounds per square inch for green
pignut hickory. The average oven-dry weight of pignut hickory is
about 51 pounds per cubic foot.
Such tests as have been made on eastern white and red oaks indi-
cate that tanbark oak in bending and crushing strength ranks about
the same as white oak and is somewhat superior to red oak.
28 CALIFORNIA TANBARK OAK.
Data are not available for a comparison of the toughness and stiff-
ness of tanbark oak and the eastern oaks and hickories.
Table 11 shows a considerable increase in the strength values of
the air-dry material over the green, and a still further increase in
these values for the kiln-dry material.
In compression perpendicular to the grain, green tanbark oak has
an average strength at the elastic limit of 1,355 pounds per square
inch. Green Douglas fir has an average strength of 651 pounds per
square inch.
In shearing strength air-dry tanbark oak shows an average of
1,960 pounds per square inch. Douglas fir has an average shearing
strength of 770 pounds per square inch for air-dry pieces.
Douglas fir would, of course, be expected to have lower strength
values than a hardwood like tanbark oak. The comparison is used
because such tests on other hardwoods have not yet been made.
SEASONING.
A number of the logs selected for testing purposes were sawed into
boards for a seasoning test. Fifty 1-inch boards were put through a
commercial dry kiln of the moist-air type in San Francisco. The
results, while encouraging as regards the behavior of tanbark-oak
lumber in a moist-air kiln, were not satisfactory, owing to the imperfect
regulation of the kiln and consequent daily variations in temperature
and humidity. After 40 days in the kiln a classification of the lumber
gave the following:
Number.
Per cent.
Good boards
28
56
Boards slightly warped
12
24
Boards checked at ends ... .
4
8
Boards badly checked
6
12
The average temperature of the kiln was only 85 F. for the 40
days, whereas it should have been at least 110 F. The loss in sea-
soning eastern oak for vehicle stock is placed at about 10 per cent.
The method of seasoning used by a lumber company which owns
considerable tanbark-oak stumpage that it is preparing to put on the
market in the form of flooring is as follows : The logs as soon as con-
venient after they come in from the woods are cut into IJ-inch
material. This is then carefully piled in the open yard, with sticks
every 18 inches, and allowed to dry from 3 to 6 months. It is finally
kiln dried from 30 to 40 days at a temperature not to exceed 110
F., when the boards are ready to be made into flooring. The kiln used
is of the blower type. The results obtained in drying tanbark oak by
this method have been very satisfactory. It should be remembered
that the trees in this case were cut during the peeling season (May to
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE VIII,
FIQ. 1. TANBARK OAK FLOORING, AND THE METHOD OF STORING AND SORTING IT.
FIG. 2. TANBARK OAK FLOORING READY FOR SHIPMENT FROM THE MILL.
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE IX.
TRANSVERSE SECTION OF A 2-YEAR-OLD TWIG OF TANBARK OAK, SHOWING TANNIN
(DARK STREAKS AND AREAS) IN THE PITH, PITH RAYS, AND BARK. MAGNIFIED 30
DIAMETERS.
Bui. 75, Forest Service, U. S. Dept. of Agriculture.
PLATE X.
FIG. 1 .TRANSVERSE SECTION OF A S-YEAR-OLD TWIG OF TANBARK OAK, SHOWING THE
DISTRIBUTION OF TANNIN IN THE PITH AND PITH RAYS. MAGNIFIED 30 DIAMETERS.
FIG. 2. LONGITUDINAL RADIAL SECTION OF A S-YEAR-OLD TWIG OF TANBARK
OAK, SHOWING THE TANNIN IN THE PITH AND PITH RAY CELLS. MAGNIFIED 30
DIAMETERS.
OCT29 1914
Division of Forestry-
University of California
SEASONING. 29
October) . It is very probable that winter-cut lumber could be sea-
soned with less loss of material.
Some of the boards and planks sawed from the logs selected for
testing were piled under shelter and seasoned for about two years,
when they were in the same condition as regards warping and check-
ing as is usually found in eastern oaks similarly handled. Some of
the lumber showed a tendency to a "blue rot," apparently caused
by too close piling, since this defect was remedied by a wider piling
that gave more circulation of air.
In the case of some 200 pieces for mechanical tests (2 by 2 by 30
inches), cut from material seasoned under shelter for two years and
then kiln dried, the pieces showed practically no checking. The
sides of the pieces were slightly depressed in a few instances, but on
the whole their condition was excellent.
All things considered, the seasoning of tanbark oak seems to offer
little, if any, more difficulty than is experienced with eastern oaks.
SHRINKAGE. ^)
In order to determine the amount of shrinkage in tanbark oak,
62 pieces (2 by 2 by 10 inches) were dried out slowly from a green
to an oven-dry condition. The pieces were selected so that two
sides were tangential to the annual rings. They were weighed and
measured at intervals for a period of about one year. The drying
was carried on first in a warm room and finally in an oven.
When a piece of green or wet wood is dried, no change in dimen-
sions takes place until a point called the fiber-saturation point 1
(generally in the neighborhood of 30 per cent moisture) is passed.
The wood then begins to shrink in cross-sectional area and continues
to do so uniformly with the removal of moisture until it is bone dry.
The longitudinal shrinkage is so small as to be negligible. Generally,
the heaviest wood shrinks the most and sapwood shrinks more than
heartwood of the same specific gravity. Shrinkage is greater in the
circumferential than in the radial direction.
The results of the shrinkage tests on tanbark oak showed an
average shrinkage in volume of 18 per cent 2 when the pieces were
dried from a green to an oven-dry condition. Of this amount about
6 per cent is radial shrinkage and about 12 per cent tangential. Air-
dry wood generally contains about 15 per cent moisture, so that the
shrinkage from the green to the air-dry state is only about half that
from the green to the absolutely dry state.
The average shrinkage in volume with red oak when dried from a
green to an oven-dry state is about the same as with tanbark oak.
Both woods vary considerably.
1 For a full discussion of the fiber-saturation point, see Forest Service Circular 108, The Strength of Wood
as Influenced by Moisture, by H. D. Tiemann.
2 This figure is based on dry volume.
30 CALIFORNIA TANBARK OAK.
HARDWOODS USED ON THE COAST.
The hardwoods at present used in the Pacific coast States come
from many foreign markets, and only a very small proportion of
them are local woods. From the Eastern States are imported oak,
ash, hickory, maple, cherry, basswood, black walnut, tulip poplar,
birch, and elm; from Honduras, mahogany; from Mexico, Mexican
mahogany, prima vera, or jenizero; from Hawaii, koa; from Aus-
tralia, iron bark (one of the eucalypts) and red bean; and from
Japan, Siberian oak.
The hardwoods from the Eastern States come for factory use in
the rough or ' i club " form; for the vehicle industry as roughly finished
parts, such as spokes, hubs, bent rims, and sawed felloes; and for
cooperage as rough staves and heading. The rest are in the form of
1-inch and 2-inch boards and 3 to 6 inch planks from 6 to 16 inches
wide and from 10 to 30 feet long. A small proportion comes in the
form of squared timbers up to 20 by 20 inches by 24 feet long. This
is for special-order work. The Mexican, Australian, Hawaiian, and
Japanese woods generally come in the shape of roughly hewn timbers,
the sizes ranging from 14 by 14 inches up to 36 by 36 inches and from
10 to 20 feet long. These rough timbers are sawed into veneer stock,
boards, and planks, as wanted.
Eastern oak makes up by far the largest amount of hardwood used
in California, with hickory next, followed by maple, ash, and cotton-
w'ood.
Some of the hardwoods have a variety of uses, while others are con-
fined to special lines. Of the eastern woods, ash, maple, hickory,
elm, and birch are used chiefly for wagon stock, only a small part
being used as lumber. Oak is largely used for cooperage, lumber,
and wagon stock, in the order named. The term "lumber" includes
boards, planks, and timbers. Oak lumber is imported for such uses
as flooring, inside finish, furniture, cabinet work, bank, store, and
office fixtures, paneling, wainscoting, picture molding, and doors.
The black walnut, cherry, and tulip poplar from the East, the prima
vera, poplar, and mahogany from Mexico, the koa from Hawaii, the
red bean from Australia, and the Siberian oak from Japan also go
very. largely into special lumber orders like the oak. Basswood is
used in the upper parts of wagons and carriages and especially for
work in pyrography.
A California-grown eucalypt, the blue gum, has been made into
insulator pins which have proved very satisfactory. It is also used
quite extensively for cordwood, to some extent for piling, and is being
tried in the form of veneer for furniture and interior finish. It is very
probable that the use of blue gum in California will be considerably
enlarged in the near future. The black cottonwood is used princi-
SUGGESTED USES. 31
pally for fruit baskets, and for this purpose is cut into veneer one-
twentieth of an inch thick. Some is made also into wagon stock.
The cost of all hardwoods is high. Ash and plain oak average $100
per thousand board feet, while quartered oak and hickory average
$125 per thousand. Iron bark brings about $105 per thousand, and
Siberian oak about $80 per thousand. This includes the cost of
transportation.
SUGGESTED USES FOB TANBABK OAK.
Up to the present time little has been known of the possibilities of
tanbark oak. The feeling has been that the wood was subject to
checking and warping to such a degree as to render its use impracti-
cable. All hardwoods are more or less subject to these defects, and
it is believed that the difficulties encountered in seasoning tanbark
will prove no greater than those which have been overcome in some
of the eastern hardwoods. In fact, the experiments made by the
Forest Service, which it must be remembered were conducted under
unfavorable conditions, showed that the wood can be seasoned in a
dry kiln in such a manner that more than half of it will be satisfactory
material and only 10 per cent badly checked.
The lumber company mentioned as manufacturing tanbark oak
flooring has had several experimental floors laid and in all cases they
have proved satisfactory under hard usage. About 200,000 feet of
flooring has been made up, and about 1,000,000 feet of lumber is in
process of drying. In sawing this lumber the regular equipment of a
redwood mill was used. Tanbark oak seems well suited for flooring.
It has a pleasing grain and color and the necessary hardness. By
using short pieces of the same length, say, from 9 to 18 inches, grooved
and tongued on the ends, as well as on the sides, the material can be
closely utilized. In laying a floor from such pieces a pleasing effect is
obtained by having each strip of flooring break joints with the strips
on each side and by alternating the light and dark pieces in each strip.
It is quite probable that tanbark oak will prove suitable for tight
cooperage. There seems to be a feeling at present that a contained
liquid would be affected by the wood, but so far as is known the wood
has not yet been given a fair trial. In regard to the tannin in the
wood, there is said to be a higher percentage in the case of eastern
white oak (1.32 per cent) l than in the case of tanbark oak (0.63
per cent). Of course there may be other constituents that render
tanbark oak unfit for use as a liquid container, but it is at least worthy
of a trial.
As an inside finish, tanbark oak has the beautiful figured grain of
other oaks, and there is apparently no reason why it should not give
i See Yearbook for 1902, U. S. Dept. of Agriculture, article entitled "Chemical Studies of Some Forest
Products of Economic Importance."
32 CALIFORNIA TANBARK OAK.
satisfaction. This seems to be proved by a number of finished speci-
mens of the wood now in the Forest Service offices in San Francisco.
The mechanical properties of tanbark oak render it suitable for
wagon and car stock. In bending and crushing strength it compares
favorably with eastern oak and hickory, which have for so long been
used in such construction. In drying it shrinks about the same
amount as red oak. Tanbark-oak bolsters for logging trucks are in
use and giving satisfaction. A number of strips of tanbark oak 1J
inches thick, 4 inches wide, and 6 feet long were steamed and bent at
a wagon factory in Oakland, Cal., with as good results as with white
oak under similar treatment.
Under present methods the price of bark f. o. b. track in the regions
of production averages $15 per cord. The fuel wood from the trees
that furnished this cord of bark would amount to about 2 cords,
worth on an average $5 per cord delivered at the nearest railroad.
Bark and cord wood together, then, would be worth $25. The 2 cords
of fuel would amount to about 1,600 feet board measure. If half of
this is suitable for boards, it is evident that with the present price of
oak lumber the returns would be greater if the tree were cut into
lumber rather than cordwood.
In conclusion, there seems to be no good reason why tanbark oak
should not take its place in the Pacific coast hardwood market for
many if not all the purposes for which eastern hardwoods are now
imported; and if this is true lumber companies owning tanbark-oak
stump age could profitably take up the utilization of this wood as
lumber. In California, particularly, where such large quantities of
hardwood are imported at a high and constantly increasing cost, a
native oak with both properties and appearance that compare favor-
ably with eastern oaks ought not to be allowed to go to waste, but
should at least be given a commercial trial.
APPENDIX.
DISTRIBUTION OF TANNIN IN TANBARK OAK.
By C. D. MELL. *
Tannin is found in most plants and almost exclusively in the living
cells, though there are some in whose cells it is not found, such as
European hackberry (Celtis australis Linn.), white mulberry (Morus
alba Linn.), black elder (Sambucus canadensis Linn.), honey locust
(Gleditsia triacanthos Linn.), black locust (Robinia pseudacacia
Linn.), and laburnum (Cytisus laburnum Linn.). It is always in
the form of a solution in the cells and not in the cell membrane, nor
in its primary membrane. Tannin, chlorophyll, and starch are
closely associated; tannin and chlorophyll together in collenchyma
and phelloderm, and tannin and starch together in the same cells in
pith rays. Tannin is most abundant in the elements outside the
cambium, and in a few cases it is present sparingly in wood fibers.
An investigation of the tannin contents of a number of trees shows
that several of the elements of tanbark oak have tannin distributed
through them, as shown in Table 12. Tannin is present in such of
the structural elements of each wood as are indicated by the letter x.
The small circle indicates that the tannin content in the element, so
marked is very small, and of no importance in connection with
commercial operations.
TABLE 12. Elements of pith, wood, and bark of trees containing tannin.
Quercus dcnsiflora Hook, and Am. (tan-
bark oak)
Alnus glutinosa (L.) Gaertn. (black alder).
Betula papyri/era Marsh, (paper birch)
Carpinus caroliniana Walt, (blue beech)...
Corylus americana Walt, (hazel)
Satix purpurea Linn, (purple willow)
Platanus occidentalis Linn, (sycamore)
Hamamelis virginiana Linn, (witch hazel).
Acer platanoides Linn. (Norway maple) ...
Rhus cotinuft Linn, (young fustic)
Pyrus communis Linn, (pear)
Eucalyptus cordata Labill . (gum )
Ribes rubrum Linn, (currant)
Syringa vulgaris Linn, (lilac)
Fraxinu* americana Linn, (white ash)
Structural elements containing tannin.
x
\
x
33
34 CALIFORNIA TANBARK OAK.
To determine correctly the distribution of tannin in plant tissue,
it is best to fix the tannin content in such a manner that it becomes
hard, compact, and easily recognizable under the microscope in
transverse and longitudinal sections. Tannin hardens into a compact
mass when treated with potassium bichromate and, in transmitted
light, has an intense red-brown color.
The ultimate twigs, obtained from growing trees, are cut length-
wise through the pith and are allowed to dry for 12 hours in a room
of ordinary temperature. Then they are soaked in a solution of
potassium bichromate for a week before the sections are cut. The
material must be treated before it is sectioned, otherwise the tannin
content will be distributed by the knife into elements where it does
not naturally occur. The color does not change when the sections
are mounted in glycerin, so the sections may be preserved in this way
for classroom or other demonstration work. The first 8 or 10 sec-
tions should be discarded, because they will include the outer cells
coated by tannin that oozed out when the twigs were first cut; and
they are likely to be disappointing because they will not show the
undisturbed tannin content. The cells in which tannin occurs will
be filled with a compact red-brown mass (Pis. IX and X) ; or there
may be only a few small red-brown globules, as in the pith ray cells
of European alder (Alnus glutinosa, L. Medic.).
An investigation of this sort shows that tannin is present in the
twigs of tanbark oak as well as in the older bark, and that tanning
extract could be made from the twigs and smaller branches, as in
the case of the eastern chestnut (Castanea dentata). Yet there is
but little tannin in the wood-parenchyma elements of the heartwood
of tanbark oak, so that tanning-extract can not be got by chipping
the wood and subjecting it to tanning-extract processes, as in the case
of the chestnut.
o
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