TDOC "ix/is AKIM UNIVERSITY LIBRARY ZTA245.7 B873 morale’! t “'* » B- 6 August1g8; "‘ \ l I R A Y SEP O 8 1987 Texas Awat uilivéfSitil Improvement of Oak - Dominated Rangeland with Tebuthiuron and Prescribed Burning a M» THE TEXAS AGRICULTURAL EXPERIMENT STATION/Neville P. Clarke, Director/The Texas A&M University System/College Station, Texas [Blank Page in Origafl Bulletin] ' w; .;\_ v ‘. , 4 r 4-: as‘ . . ‘~: a \\_ x \ \ , ,_ Improvement of ()ak-Dominated Rangeland with Tebuthiuron and Prescribed Burning Authors CHARLES I. SCIFRES, Thomas M. O'Connor Professor Texas Agricultural Experiment Station (Department of Range Science) ]ERRY W. STUTH, Professor Texas Agricultural Experiment Station (Department of Range Science) BEN H. KOERTH, Research Associate Texas Agricultural Experiment Station (La Copita Research Area) Contents Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3 Q The Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Study Site Description and Treatment Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Vegetation Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Analysis of Wildlife Habitat Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Analysis of Cattle Diets and Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Rainfall Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Woody Plant Responses to Brush Management Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Herbaceous Vegetation Responses to Brush Management Treatments . . . . . . . . . . . . . . . . . 8 Cattle Performance and Diets Following Tebuthiuron Application . . . . . . . . . . . . . . . . . . . . 12 Postburn Diet Selection by Cattle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Influence on Wildlife Habitat Attributes . . . . . . . . . . . . . . . .' . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Influence of Tebuthiuron/Prescribed Burning on Watershed Attributes . . . . . . . . . . . . . . . . 18 Integration of Prescribed Burning with Tebuthiuron Applications . . . . . . . . . . . . . . . . . . . . 18 Economic Comparison of Brush Management Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Ecological, Economic, and Management Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 Appendix A. Scientific Names of Plants and Animals Mentioned in Text . . . . . . . . . . . . . . . .23 Appendix B. Conversion of Metric to English Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 Q w. Q Excessive cover of post oak, blackjack oak, and associated woody species limit cattle production on about 4.5 million hectares in the eastern third of Texas. Aerial applications of tebuthiuron pellets at 2.2 or 4.4 kg/ha (active ingredient) control the oaks and several species of understory shrubs, and grass production may increase significantly within a growing season after tebuthiuron application. However, tebuthiuron- tolerant species, especially vines such as saw green- brier, southern dewberry and peppervine, increase in abundance following control of the overstory trees and associated shrubs with tebuthiuron. In addition, the understory shrub American beautyberry may increase dramatically on sites after aerial application of tebuthiuron. The increase in tebuthiuron-tolerant vines, the spread of American beautyberry, and the invasion of other woody species may negate grass production within 3 years after release by herbicide treatment. Prescribed burning as headfires in late winter within two growing seasons after tebuthiuron application, and at regular intervals thereafter, sup- presses the development of secondary woody plant Summary stands. Prescribed burning has little effect on infiltra- tion rates, sediment production, or nutrient loss in runoff on near level sandy loam sites. Forage produc- tion and cattle weight gains may not be increased until the growing season following tebuthiuron applica- tion, especially after treatment of heavy brush stands. Follow-up burns should extend animal performance into the fall when available nutrients are typically less than required for maintenance of growing and lactat- ing cattle. Apparently, control of the forbs and browse in heavy brush canopies without increased produc- tion of grasses accounts for reduced cattle perform- ance during the first growing season after tebuthiuron application. Tebuthiuron can be applied in strips or other suitable patterns to prevent negative alterations in habitat for white-tailed deer and sustain nutrient intake of cattle. Treated strips probably should be no wider than 325 meters (m) and alternate with un- treated strips at least 80 m wide. Populations of small rodents, such as cotton rats and wood rats, are cyclic following tebuthiuron application in response to shifts in vegetal cover. The Problem The Texas Post Oakl Savanna, a land resource of about 3.2 million hectaresz (ha), was originally open grassland dotted with stately, indi- vidual oak trees or with small scat- tered clusters of oaks (Gould 1975). Potential vegetation of these highly productive grasslands includes mid- and tall grasses such as little bluestem, indiangrass, Texas win- tergrass, and purpletop. Species of Chasmanthium and low-growing Panicums occur in the heavily wooded areas, especially along the drainages and waterways. Heavy cover of post oak and blackjack oak in association with various other trees and shrubs also occurs on the Coastal Prairie and Cross Timbers regions, limiting production of livestock on about 4.5 million ha in the eastern third of Texas (Scifres and Haas 1974). Restriction of naturally- occurring fires in conjunction with overgrazing by livestock, often continuous for prolonged periods, and periodic droughts of various durations are largely responsible for creation of dense thickets over much of the Post Oak Savanna (Scifres 1980). The densities of post and blackjack oaks have increased and the woody stands are further thickened by establishment of yaupon, winged elm, honeylocust, common persimmon, downy haw- thorn, gum bumelia, tree huckle- berry, eastern redcedar, buck- brush, willow baccharis, American beautyberry, Texas ‘persimmon, and various other trees and shrubs. Vines, especially saw green- brier, peppervine, and southern dewberry, grow with the shrubs to form impenetrable thickets on some sites. Dense woody cover has 1 Scientific names of plants and ani- mals mentioned in text are given in Appendix A. Conversions of metric to English units are given in Appendix B. 4 reduced the carrying capacity for cattle to 1 animal unit (AU)3 per 14 to 16 ha (35 to 40 acres) on land that, in good range condition, could support 1 AU per 4 to 5 ha (10 to 12 acres). Invading grasses in- clude red lovegrass, broomsedge bluestem, splitbeard bluestem, and smutgrass. Common broad- leaf species include bullnettle, yan- keeweed, and western ragweed. Mechanical clearing of the brush (dozing, raking, stacking, and burning the stacks) and establish- ment of tame pastures with com- mon bermudagrass, bahiagrass, or dallisgrass is commonly practiced in the region. Methods for conver- sion of the woodlands to native grasslands have included dozing, chaining, and application of her- bicides. Prior to the early 1970's, the primary herbicide treatment was aerial application of 0.8 to 1.1 kilograms per hectare (kg/ha) of 2,4,5-T [(2,4,5-trichlorophenoxy) acetic acid] for two or three con- secutive growing seasons (Darrow and McCully 1959). The first herbicide application ef- fectively removed the oak over- story. The second and third treat- ments were applied to control the understory shrubs. The applica- tion of a mixture containing equal parts of picloram (4-amino-3,5,6- trichloropicolinic acid) and 2,4,5-T at 1.1 kg/ha total herbicide was more effective than 2,4,5-T applied alone (Scifres and Haas 1974), but the proximity of herbicide suscepti- ble crops and public concern about use of 2,4,5-T restricted spraying over much of the Post Oak Savan- na. Further, cessation of produc- tion of 2,4,5-T for domestic use in 1984 necessitated development of alternative practices for improve- ment of range vegetation in the region. 3 Animal unit (AU) is defined as 454 kg (1,000 lb) cow with calf or equivalent. Tebuthiuron fl-[S-Ll-dimeth- ylethyl)-1,3,4-thiadiazol-2-yl]-fl- fl-dimethylurea] was registered in 1979 by the Environmental Protec- \ W tion Agency for control of brush species including oaks on range- land. It is formulated as an extruded pellet containing 20 per- cent active ingredient (ai). Tebuthi- uron is readily absorbed by plant roots (Steinert and Stritzke 1977) and translocated to the foliage where it inhibits photosynthesis. Many species of oaks, including post oak and blackjack oak, are susceptible to the herbicide applied broadcast (Scifres et al. 1981a), in grids (Stritzke 1976), or subsurface in rows (Meyer et al. 1978). Since tebuthiuron was intro- duced as a potential herbicide for brush management on rangeland, considerable research has been conducted to define appropriate dosages for brush control, forage and livestock responses to its appli- cation, and other factors affecting tebuthiuron use. This publication collates the available literature on tebuthiuron use for improvement of rangeland dominated by oak- mixed hardwoods and reports the results of long-term experiments with the herbicide in light of other research data. Experiments were established on the Native Plant and Animal Conservancy, Texas A&M Univer- sity campus, in 1977 and 1978 to (1) evaluate vegetation and cattle re- sponses to tebuthiuron application and (2) provide a basis for design- ing long-term brush management systems for the Post Oak Savanna, giving due attention to wildlife. Preliminary data from these exper- iments have been reported (Scifres et al. 1981a, 1981b; Kirby and Stuth 1981). Additional data collected from 1981 through 1984 and gener-wl al observations through 1986 are * presented in light of the initial findings. Q Study Site Description and Treatment Installation Tebuthiuron pellets (20 percent active ingredient [ai]) were aerially applied at 2.2 kg/ha to two pastures of approximately 2 ha each on May 9, 1977. Woody plants were dozed into stacks in a second pair of pas- tures during May and Iune 1977. The mechanically-cleared pastures were shredded in Iune 1982. Pas- tures were randomly selected for treatment from among six, leaving two pastures untreated, so that the experiment was arranged as a ran- domized complete block with two replications. Woody canopy cover at initiation of the research was composed of an overstory of post and blackjack oaks. The understory included yaupon, winged elm, gum bume- lia, buckbrush, water oak, willow baccharis, downy hawthorn, saw greenbrier, American beautyberry, honey locust, common persim- mon, cedar elm, Texas persimmon, and southern dewberry with occa- sional honey mesquite and eastern redcedar. The replicates were stra- tified to account for differences in topography with one on nearly level terrain and the other with slope varying from 2 to 7 percent. Soils, primarily sandy loam to fine sandy loam of the Lufkin-Axtell- Tabor series (Udertic Paleustalfs), contained 49 percent sand, 13 per- cent clay, and 1.3 percent organic matter with a pH of 5.5 to 5.6 in the surface 15 cm (Scifres et al. 1981a). Clay content increased with depth to 35 percent at 60 cm and sand content decreased to 28 percent. In late February 1979, 1981, and H1984, the pastures treated with ebuthiuron in 1977 were burned with headfires. The mechanically- treated pastures were burned in Materials and Methods the winter 1984. Immediately prior to burning, standing fine fuel was harvested and mulch collected from twenty-five to fifty 0.25-m2 plots, equidistantly spaced down the center of each pasture. At the same time, 10 to 25 fine fuel sam- ples and soil samples to 8 cm deep were collected for determination of water content. Soil and fuel sam- ples were weighed wet, then oven- dried at 60 degrees centigrade (°C), and reweighed. Environmental variables monitored during the burns included air temperature, in- stantaneous wind speeds with a hand-held anemometer, and rela- tive humidity with a psychrometer. Maximum fire temperatures were recorded at 10 to 25 selected points in 1979 and 1981 with heat- sensitive- tablets and at 15 points with continuously recording ther- mocouples in 1984. Tebuthiuron pellets (20 percent ai) were applied at 0, 2.2, or 4.4 kg/ha in a second experiment to duplicate, 3.2-ha plots on April 7, 1978. The study site was less than 5 kilometers (km) from the first, and the woody canopy cover averaged 6O percent. Species present were the same as for the experiment established in 1977 except that east- ern redcedar commonly occurred in the woody plant stands and hon- ey mesquite was rare. Topography was rolling with slope varying from 2 to 5 percent. Soils were primarily sandy loams of the Ax- tell-Tabor series with textural char- acteristics similar to those de- scribed for the 1977 study site. The pastures treated in 1978 were subdivided into equal parts during the summer 1980. Pre- scribed burns were installed as headfires in February 1981 and 1984 to two of the four pastures receiving each of the treatments. Variables were monitored as de- scribed for burns applied to the 1977 study area. Vegetation Evaluation Changes in canopy cover, densi- ty, and frequency of live woody plants were evaluated in the fall using the point-centered-quarter method (Cottam and Curtis 1956) from 1977 through 1984. The dis- tance to the nearest woody plant in each quadrant and reduction in its canopy were recorded at 25 to"50 points equally spaced down the center of each plot. In addition, canopy reduction of woody plants occurring in a 20-meter (m)-wide belt down the center of each plot was estimated by two workers. Canopy intercepts of 1-m-tall and shorter shrubs were recorded along ten 33-m lines in ]une 1984. Distance to the nearest American beautyberry plant, its height, and number of basal stems were re- corded at 200 points equidistantly spaced down the center of each pasture in May-]une 1983. The nearest overstory species within 2 m of the American beautyberry plant was also recorded. Mean values for canopy cover, stems/ha, and height of American beautyber- ry plants from treated areas were compared to those on untreated pastures, using least significant difference (LSD) (P s 0.05). Within 30 days after application of tebuthiuron on each experi- ment, 20 to 25 circular grazing exclosures (1.3 m in diameter and 2 m tall) were equally spaced along a line down the center of each pasture. Standing herbaceous crops were harvested to a 2.5-cm stubble height in a 0.25 m2 area from the center of each exclosure. The exclosures were then relocated 1 m away from the original points 5 based ‘on random selection of a cardinal direction. Standing crops were separated into grasses and forbs, dried at 6O °C for at least 48 hours and weighed. Data collected through the 1980 growing season are reported by Scifres et al. (1981a, 1981b). Subsequent evaluation dates for the area treated in 1977 were ]uly 17 and November 26, 1981; Iuly 15, August 30 and De- cember 20, 1982; and November 20, 1983. Pastures treated in 1978 were evaluated on May 18 and Novem- ber 8, 1981; May 31, August 30, and December 7, 1982; May 16 and N o- vember 3, 1983; and May 2, 1984. Standing crop data were subjected to analysis of variance and means were separated by Student- Newman-Keul’s procedure (P s 0.05) (Steel and Torrie 1960). Each time standing crop was har- vested, basal cover of herbaceous species was recorded from fifty, inclined, 10-point-frame samples spaced equidistantly down the center of each pasture. Species cov- er was expressed as proportions represented by grazing value cate- gories (good-to-excellent, fair, or poor) based on published assess- ments (Gould and Box 1965, Hoff- man et al. 1970). Within each year of evaluation, cover values for little bluestem and brownseed pas- palum were summed for the exper- iment initiated in 1978. The propor- tion of the sum represented by little bluestem was transformed (\/X+0.5), and means of burned and unburned pastures not treated with tebuthiuron were contrasted using a t-test. The same compari- sons were developed for burned and unburned pastures which had been treated with tebuthiuron. Analysis of Wildlife Habitat Features Changes in woody canopy and herbaceous productivity offer in- sights about the influence of manipulation of the brush stands on food and cover for wildlife. Sen- zota (1985) evaluated variation in habitat attributes and the influence on small mammals on the study site. In addition, differences in screening cover in September 1985 among pastures treated in 1978 were evaluated for this study. Screen closure was determined with a 2-m—tall, 15-cm—wide board with alternating black and white, 50-cm segments. Distance required to obscure 100 percent of the board was measured in two opposite di- rections from 5O equidistantly- spaced points down the center of each pasture. Data were subjected to analysis of variance and means separated by Student-Newman- Keul’s test (P€0.05). Analysis of Cattle Diets and Performance A simulated high-intensity, low frequency grazing scheme (7- pasture,1—herd, 20 to 21 days graze, 130 to 180 days rest) was implemented for all experiments. Pastures were grazed by eight, pre- conditioned steers weighing ap- proximately 200 kg in 1977 and 1978. However, following burning in 1981 and 1984, 350 to 400 kg cows were used. Grazing studies on pastures treated in 1977 and 1978 were initi- ated in the fall following herbicide application in the spring. Grazing was terminated in each trial when 50 percent utilization was observed on the key management species, which were brownseed paspalum " the year of treatment and little bluestem in subsequent years. Grazing was initiated during spring following the late winter burns in 1981 and 1984. Utilization did not exceed 50 percent in the 1981 study. A ”complete graze—out" of herbaceous forage was enforced for purposes of the 1984 study. Animal performance data were obtained by weighing new groups of steers before and after each sea- son of each experiment. Data were expressed as average daily gains (ADG) (kg/steer/day), total daily gains (TDG) (kg/ha/day), and days of available grazing. Days of graz- ing is defined as the number of days a pasture supplied herbage for a given number of steers based on proper forage use, expressed herein as steer days/ha. Animal performance data were not collect- ed in 1981 or 1984. Four esophageally fistulated cows or steers were utilized in grazing trials during 1977, 1978, 1981, and 1984 to collect extrusa for botanical and nutritional analyses. Dietary samples were mixed, dried at 60 °C for 48 hours, and two subsamples removed. One sub- sample was ground to pass a 1-mm screen and subjected to crude pro- tein (CP) analysis (AOAC 1970) and in vitro digestible organic mat- ter (IVDOM) analyses (Tilley and Terry 1963, Van Soest and Wine 1967). The other subsample was subjected to macrofragment analy- sis to determine composition of diets selected by the animals (Lopes and Stuth 1984). H Rainfall Pattern Rainfall at the study ‘site during 1977 was 72 percent of the long- term average (Table 1). About 27 percent (19.5 cm) of the total annu- al rainfall was received in April 1977, the month prior to tebuthiuron application. However, rainfall during the 30-day period following tebuthiuron application apparently was adequate to sol- ubilize the herbicide and move it into the soil profile. As a result, symptoms of tebuthiuron phy- totoxicity were uniformly apparent on woody plants by midsummer. Rainfall in 1978 was 81 percent of the long-term average (Table 1). Rainfall in May-]une 1978 was slightly greater than it was during the previous year, and September- October rainfall exceeded 14 cm. The winter-spring of 1979 was relatively wet with more than 10 cm/month received from Ianuary to April and with about 26 cm in May (Table 1). Rainfall in Iuly, 17.9 cm, accounted for the summer (Iune-Iuly-August) 1979 being the Results and Discussion wettest (29.2 cm) during the years of study. Rainfall during the spring (March-May) and fall (September- October) growing periods is critical to forage production. Spring rain- fall varied from 17.6 cm in 1978 to 50.6 cm in 1979, and averaged 30.1 cm for 1977 through 1984 (Table 1). Fall rainfall ranged from 8.9 in 1977 to 34.1 cm in 1984, and averaged 21.1 cm for 1977 through 1984. Rainfall during the study period was typical of the long-term pat- tern. Annual rainfall from 1977 through 1984 averaged 98 cm com- pared to the long-term average of 99.4 cm (Table 1). As is normal for the region, relatively dry years were bound by extremely wet years. Woody Plant Responses to Brush Management Treatments Prior to tebuthiuron application in 1977, the woody plant canopy cover was 43 percent, 22 percent oaks and about 7 percent yaupon. Initial canopy cover on the site treated in 1978 was 60 percent. Tebuthiuron pellets at 2.2 kg/ha in both experiments and at 4.4 kg/ha applied in 1978 effectively controlled post oak, blackjack oak, water oak, winged elm, yaupon, downy hawthorn, gum bumelia, and willow baccharis (Scifres et al. 1981a). By the end of the second growing season after application, the canopies of these species were reduced by no less than 95 percent. On the average, tebuthiuron'"re- moved 90 percent of the overall woody canopy by the second growing season after application on both study areas. Species not effectively controlled by tebuthiuron included honeylo- cust, saw greenbrier, common per- simmon, American beautyberry, peppervine, and southern dewber- ry. These species accounted for a low proportion of woody cover so that initial overall reduction by the herbicide applications exceeded 85 percent. However, the abundance of American beautyberry and of Table 1. Monthly rainfall received on the study pastures where tebuthiuron-prescribed burning systems for improvement of thicketed post oak savanna were evaluated from 1977 through 1984 near College Station, Texas Precipitation (cm) Month 1977 1978 1979 1980 1981 1982 1983 1984 January 4.9 9.5 10.3 8.2 7.4 2.2 10.3 4.0 V February 8.4 7.2 10.8 4.4 3.8 3.7 7.9 2.4 B’ March 4.8 8.5 12.2 15.4 4.3 8.4 14.1 8.8 April 19.5 5.3 12.7 4.8 2.8 11.0 1.2 0.2 May 2.0 5.8 25.7 13.3 12.9 14.3 28.9 11.8 lune 7.8 8.4 4.9 0.2 28.3 5.3 8.0 13.1 luly 0.2 1.3 17.9 0.5 7.4 5.8 8.0 1.0 August i 4.1 1.5 8.4 0.9 9.3 4.8 12.8 7.1 September 4.4 13.5 10.5 11.2 9.3 4.0 18.8 1.3 October 4.5 0.9 3.7 5.1 21.8 18.9 10.3 32.8 November 6.9 15.6 7.8 9.3 4.0 7.6 7.3 6.1 \ December 5.4 7.3 7.5 0.8 0.8 8.8 4.1 9.1 Total 72.0 80.5 130.2 73.7 109.9 92.8 127.5 97.5 Deviationl -27.4 -18.9 31.5 -25.8 10.3 -7.0 27.9 -1.9 ‘Deviation from average rainfall for 1950 through 1976. Table 2. Canopy cover, stem densities, and heights of American beautyberry and overstory associates in May-June 1983 after aerial application of tebuthiuron pellets in May 1978 near College Station, Texas American beautyberry 0 . . Tebuthiuron Canopy Frequency ( /o) of associated species rate cover Height Yaupon- Site (kg/ha) (%) Stems/ha (m) Oak Yaupon oak Others Upland 0 5 338 1.6 16 14 7.0 0 2.2 94* 10,399* 1.2* 0 0 10D 0 V, 4.4 95* 10,307* 1.2* 0 11 89 0 g Lowland 0 6 331 1.9 6 17 74 3 2.2 17* 1,833* 1.5* 7 24 70 0 4.4 12* 1,267* O.9* 1O 36 48 6 ‘Significantly different (LSD=0.05) from means representing no herbicide treatment. vines, especially saw greenbrier, increased dramatically by the third growing season after tebuthiuron application. At initiation of the research, canopy cover of American beauty- berry varied from 5 to 7 percent. Although the tebuthiuron applica- the fall 1983, after aerial application of tebuthiuron pellets in 1978, ranged from 6.6 to 9.2 percent com- pared to less than 1 percent on untreated pastures (Table 3). Pre- scribed burning of the herbicide- treated pastures had no effect on the southern dewberry canopy Table 3. Proportion (%) of foliar cover as southern dewberry in September 1983 after aerial application of tebuthi- uron pellets in May 1978 and pre- scribed burning in February 1981 near College Station, Texas Tebuthiuron rate (kg/ha) tions defoliated the plants, most of cover. Although vines were not in- Burned 0 2'2 4'4 the American beautyberries sur- cluded in measurements in sum- No ()_1 92* 55* vived the treatment. By early sum- mer 1984, it was estimated that saw Yes 0Q 3_9* 9_4* mer 1983, American beautyberry canopy cover was 2- to 3-fold great- er on treated than on untreated lowlands (Table 2). American beautyberry stem densities exceeded 10,000/ha in 1983 on up- lands treated with tebuthiuron in 1978, roughly 30 times the stem density on untreated upland sites. In most cases, American beauty- berry was growing beneath yaupon plants, oaks, or a mixture of oaks and yaupon. Control of overstory woody plants with tebuthiuron apparently released American beautyberry to form con- tinuous canopy cover on the up- land sites. On the average, the American beautyberry plants were shorter on treated than on un- treated pastures in 1983, indicating that a large proportion of the in- crease was the result of seedling establishment, apparently shortly after tebuthiuron application. The height difference was particularly pronounced on lowland sites. The abundance of vines, espe- cially southern dewberry, pepper- vine, and saw greenbrier, also in- creased following tebuthiuron ap- plications. For example, the pro- portion of woody plant cover at- tributed to southern dewberry in 8 greenbrier, peppervine, southern dewberry, and poison ivy account- ed for more than 20 percent of the woody plant cover on tebuthiuron- treated plots, regardless of burning treatment. Saw greenbrier alone accounted for 10 to 12 percent of the cover in 1984 on pastures treated with tebuthiuron in 1978. Not considering the influence of vines, canopy cover of woody plants in late summer 1985 aver- aged about 52 percent and 25 per- cent on plots treated with 2.2 and 4.4 kg/ha of tebuthiuron, respec- tively, in 1978 (Table 4). Cover on tebuthiuron-treated pastures which were not burned was dominated by American beauty- berry. Values in Table 4 represent the weighted average of lowland and upland areas. American beautyberry canopy cover aver- aged less than 2 percent on un- treated pastures, about 37 percent on pastures treated with 2.2 kg/ha of tebuthiuron, and 27 percent on pastures treated in 1978 with the higher application rate. In contrast, American beauty- berry canopy cover averaged 6 and 4 percent, respectively, on pastures treated with 2.2 and 4.4 kg/ha of the herbicide and then burned in *Significantly different (LSD=0.05) from means representing no herbicide treat- ment. the winters of 1981 and 1984. Pre- scribed burning also removed most of the eastern redcedar less than 4 m tall. As a result, total woody cover, not considering vines, aver- aged about 13 and 5 percent, re- spectively, where 2.2 and 4.4 kg/ha of the tebuthiuron pellets were ap- plied in 1978 and pastures were burned in the winters of 1981 and 1984. Woody species with canopy cover less than 0.1 percent were not included in the summary (Table 4). These minor species included honey mesquite, black locust, pricklypear, and chinese tallow, which were most common in plots treated with 2.2 kg/ha of tebuthiuron but not burned. Herbaceous Vegetation Responses to Brush Management Treatments Tebuthiuron at 2.2 kg/ha in 1977 Q did not alter average grass stand- \ ing crop during the growing sea- son of treatment (Scifres et al. \ J \ 1981b). However, grass standing crop on treated pastures was ap- proximately four times that of un- treated plots at 1 year after her- bicide application, and the increase in forage production was main- tained through the second and third years after treatment. Grass standing crop in July 1981 on pastures aerially treated with tebuthiuron at 2.2 kg/ha in 1977, followed by burning in the winters of 1979 and 1981, was roughly twice that of areas that were un- treated or mechanically cleared in 1977 (Table 5). Pretreatment woody cover on these pastures averaged about 40 percent. Grass standing crops were maintained on the chemically-treated pastures into the fall and were greater than those on the untreated or on adjacent mechanically-treated pastures. The same general pattern occurred Table 4. Canopy cover (%) of major woody species in lune-July 1985 following aerial application of tebuthiuron pellets at 2.2 or 4.4 kg/ha on May 11, 1978, and prescribed burning in late February 1981 and 1984 of thicketed post oak savanna near College Station, Texas Tebuthiuron rate (kg/ha) No burn Burn Species 0 2.2 4.4 0 2.2 4.4 Post Oak 7.5 0.2 0 14.7 0.1 0 Blackjack oak 3.0 0 0 5.4 0 0 Water oak 1.8 0 0 1.5 0 0 American beautyberry 1.7 36.8 26.6 1.8 6.4 3.6 Black willow 0 0 0 0.1 0 0 Buckbrush 0.3 0 0.1 0.8 0 0 Chinaberry 0 0 0.9 0.3 0 0 Chinese elm 1.2 0 0 1.1 <01 0 Common persimmon 0.3 1.1 0.7 1.1 0 0 Eastern redcedar 2.1 8.1 4.2 3.1 3.1 1.2 Farkleberry 0.3 0 0 0.3 0 0 Gum bumelia 0.3 0.2 0.1 0.5 0 0 Honeylocust 0.3 0.4 0.5 0.3 0 0 Possumhaw 0.6 0 0 2.1 <0.1 0 Sugar hackberry 0.3 0 0 0.3 0 O Willow baccharis 1.8 2.9 1.4 2.6 2.3 0.2 Winged elm 0.4 0 0 1.5 0 <0.1 Yaupon 27.7 2.5 0.5 14.4 0.6 <0.1 Total cover (%) 59.7 52.2 25.2 51.6 12.7 5.1 in mid-summer 1982, except that the grass standing crops on the mechanically-treated pastures were no different from those on pastures treated with tebuthiuron. Enhanced grass response on the mechanically-treated pastures was attributed to the influence of shredding the previous spring. However, grass standing crops on mechanically-treated and un- treated pastures were no different by late August 1982. Suppression of grass standing crop by the end of the growing season after shred- ding indicates the extremely rapid topgrowth replacement by woody plants in this region. By fall 1983, grass standing crop averaged 4,262 kg/ha on the herbicide-treated areas providing ample fine fuel for prescribed burning the following winter. Standing fine fuel loads on mechanically-treated pastures was about half that on pastures treated with tebuthiuron. Forb standing crops were unaf- fected by tebuthiuron application during the first growing season but were greatly reduced during the second and third growing season after treatment in 1977 (Scifres et al. 1981b). Forb standing crops did not differ among treatments at 3 years after tebuthiuron application in 1977. Forb standing crops on pastures which had been treated with tebuthiuron in 1977 were consis- tently greater than standing crops on untreated pastures, regardless Table 5. Oven-dry herbaceous standing crops (kg/ha) at various dates after aerial application 0f tebuthiuron at 2.2 kg/ha in May 1977 followed by prescribed burning in February 1979 and 1981 com dozing in lune-luly1977 and shredded in March-April 1982, near College Stati pared to pastures with brush removed by on, Texas Standing cropsl 1981 1982 1983 "Treatments(s) luly17 Nov. 26 July 15 Aug. 30 Dec. 20 May8 Nov. 10 Grasses None 1,076 a 832 a 990 a 750 a 820 a 600 a 1,690 a Tebuthiuron-burn 2,596 b 3,268 c 1,984 b 2,412 b 2,800 b 2,812 c 4,262 b Doze, stack-shred lj 1,323 a 1,462 b 1,508 b 830 a 1,170 a 1,413 b 2,150 a Forbs None 472 a 149 a 52 a 40 a 34 a 76 a 46 a Tebuthiuron-burn 648 ab 415 b 90a 586c 84a 112a 196b Doze, stack-shred 984 b 491 b 252 b 120 b 68 a 82 a 161 b l Means within a growth form and date of evaluation followed b Newman-Keul’s test. y the same letter are not significantly different (P<0.05) according t0 Student- of season of evaluation from 1981 through 1983 (Table 5). Except for the spring following the shred- ding, forb standing crops were the same or greater on the herbicide- treated and burned pastures than on those treated mechanically. There was no difference in grass standing crops among treatments at 4 months after application of tebuthiuron pellets at 2.2 or 4.4 kg/ha in 1978 (Scifres et al. 1981b). Grass standing crops at 13 months after treatment were increased, compared to untreated pastures, where the herbicide was applied at 2.2 kg/ha. However, grass produc- tion was not increased on pastures treated with 4.4 kg/ha, compared to that on untreated pastures. The lack of difference was attributed to suppression of grass production in localized areas on pastures treated with the higher herbicide dosage. Furthermore, grass production was highly variable within pas- tures treated with 4.4 kg/ha of tebuthiuron. Large bare spots oc- curred near robust individuals of grasses which were tolerant of the herbicide. However, by the end of the second growing season, grass standing crop was greater on pas- tures treated with 4.4 kg/ha than on those treated with the lower her- bicide rate and was greater on treated than untreated pastures. This difference among treatments also occurred at 30 months after herbicide application (Scifres et al. 1981b). There were no differences in grass standing crops in May or November 1981 on pastures treated with 2.2 or 4.4 kg/ha of tebuthiuron in 1978, and standing crops on treated pastures were about 10-fold greater than those on untreated pastures (Table 6). Forb standing crops were greater on herbicide-treated than on un- treated pastures in both spring and fall 1981. Prescribed burning of previously untreated pastures in February 1981 did not alter grass standing crops the following grow- ing season, compared to un- burned, brush-dominated pas- tures. Standing fine fuel loads were inadequate and the fuel too discon- tinuous to carry an effective fire. Thus, the fires were restricted al- most solely to surface fuels, primarily leaf litter, and were ”cool" and spotty. Grass standing crops were re- duced in May 1982 following the burns in the winter 1981 on her- bicide-treated plots, compared to those pastures treated with tebuthiuron and not burned (Table 6). Grass standing crops had re- covered by August 1982 on pas- tures that had been treated with tebuthiuron in 1978 and burned in the winter 1981. Increased grass standing crops on the burned pas- tures were maintained until De- cember 1982 and were especially evident on pastures that had been treated with 4.4 kg/ha of tebuthiuron. The second burn in February 1984 of the area treated in 1978 did not alter grass standing crops on brush-dominated pastures (Table 6). Fire behavior during the second burn was the same as with the burn in 1981. These data indicated the necessity of removing the woody plant canopy to release fine fuel for most effective burning post oak- mixed hardwoods. The burns in 1984 were more effective than those in 1981 when applied to pas- tures treated with tebuthiuron in 1978. Grass standing crops in May 1985 were greater on pastures treated with tebuthiuron and burned, and there was no dif- ference attributable to application rate of tebuthiuron. Standing crops in the fall were greatest where 4.4 kg/ha of tebuthiuron were fol- lowed by prescribed burning but did not differ among the other her- bicide-burning treatments. Table 6. Oven-dry standing crops of grasses and forbs at various dates after aerial application of tebuthiuron pellets at 2.2 or 4.4 kg/ha on May 11, 1978, and prescribed burning in late February 1981 and 1984 of post oak-mixed hardwoods near College Station, Texas Standing cropsl 1981 1982 1983 1984 Treatment May18 Nov. 8 May 31 Aug. 30 Dec. 7 May16 Nov. 3 May 2 Grasses None 96 a 231 a 134 a 184 a 182 a 94 a 206 a 88 a Prescribed burn - - 112 a 266 a 226 a 116 a 217 a 89 a Tebuthiuron (2.2 kg/ha) 1,136 b 2,000 b 848 bc 1,162 b 1,162 b 1,006 b 2,650 bc 2,047 b Tebuthiuron (2.2 kg/ha)-burn — — 544 ab 1,404 c 1,412 b 1,812 c 2,823 c 1,355 b Tebuthiuron (4.4 kg/ha) 1,192 b 2,965 b 1,268 c 1,376 c 2,076 c 1,127 b 2,375 b 2,417 d Tebuthiuron (4.4 kg/ha)-burn — — 694 abc 1,816 d 2,786 d 2,103 c 3,516 d 1,317 b Forbs None 50a 47a 34a 24a 150 b 54a 36a 16a Prescribed burn — — 30 a 35 a 322 e 57 a 48 a 24 a Tebuthiuron (2.2 kg/ha) 358b 865c 164b 198b 56b 167 bc 270b 150b Tebuthiuron (2.2 kg/ha)-burn - — 258d 579c 96c 184C 298b 363c Tebuthiuron (4.4 kg/ha) 312 b 375 b 204 c 193 b 6 a 115 b 262 b 149 b Tebuthiuron (4.4 kg/ha)-burn - — 326e 534c 10a 213 e 270b 441 c l Means within a forage category and within a date of evaluation followed by the same letter are not significantly different (P<0.05) according to Student-Newman-Keul’s range test. 1O 5n Forb standing crops were re- duced the growing season after ap- Qalication of 4.4 kg/ha of “tebuthiuron in 1978 (Scifres et a1. 1981b). Forb standing crops did not differ among treatments at 25 months after herbicide application but were greater on herbicide- treated than on untreated pastures after 30 months. Forb standing crops following burning in 1981 of pastures treated with tebuthiuron in 1978 showed the same trends as grasses (Table 6). Burning of brush-dominated plots had no effect on forb standing crops in May or August 1982. Burn- ing of tebuthiuron-treated pas- tures increased forb standing crops at both the spring and fall sam- plings, compared to untreated pas- tures. However, standing crops of forbs in the winter 1982 were uni- formly low on tebuthiuron-treated plots, regardless of herbicide rate or burning treatment. This reduc- tion was attributed to the increased standing crop of grasses on the treated pastures. Proportion of the grass stand as species of good-to-excellent graz- ing value varied little on untreated pastures, accounting for 2 to 4 per- cent of the total cover each year (Table 7). The proportion of species of fair grazing value accounted for Table 7. Estimated proportion of grasses by grazing value based on percentage foliar cover from 1981 through 1984 after aerial application of tebuthiuron pellets in May 1978 and prescribed burning in late February 1981 and 1984 near College Station, Texas Tebuthiu ron rate (kg/ha) Forage category 0 2.2 4.4 0 2.2 4.4 Unburned Burned 1981 Good-to-excellent 2 26 29 16 24 22 Fair 55 5O 56 69 54 75 Poor 43 24 15 15 22 3 1982 Good-to-excel lent 4 7 13 4 15 13 Fair 63 7O 62 9O 66 63 Poor 34 23 25 6 19 24 1983 Good-to-excellent 3 6 6 2 14 15 Fair 68 74 76 93 81 78 Poor 29 20 18 5 5 7 1984 Good-to-excel lent 4 8 8 5 16 16 Fair 58 72 80 61 68 74 Poor 38 2O 12 33 16 10 Table 8. Percentage of the total foliar cover of little bluestem plus brownseed paspalum contributed by little bluestem in the fall (September-October) 1981 through 1984 following tebuthiuron application at 2.2 kg/ha in 1978 and prescribed burning in late February 1981 and 1984 near College Station, Texas 55 to 68 percent of the total foliar cover. Burning in the winter 1980 caused a relatively rapid increase in the proportion of species highly desirable for grazing, primarily by promoting vegetative growth of lit- tle bluestem. However, the propor- tion of species of good-to-excellent grazing value in 1982 and 1983 was no different on burned and un- burned pastures that had not been treated with the herbicide. The proportion of species of good-to-excellent grazing value on pastures treated with tebuthiuron in 1978 and not burned averaged 26 to 29 percent in 1981 but only 8 percent in 1984 (Table 7). In com- parison, pastures treated with tebuthiuron in 1978 and burned in 1981 contained grass stands with 16 percent of the foliar cover pro- vided by species of good-to- excellent grazing value. Much of the variation in the pro- portion of species of good-to- excellent grazing value caused by treatment can be explained by the shifting ratio of little bluestem to brownseed paspalum foliar cover. Since this ratio was not influenced by herbicide rate (i.e. 2.2 compared to 4.4 kg/ha), pastures receiving 2.2 kg/ha are compared to untreated pastures (Table 8). Data represent- ed that proportion of the sum of the cover of the two species that was represented by little bluestem. The proportion of little bluestem in re- lation to brownseed paspalum in untreated pastures increased from 1981 through 1984 (Table 8). This was attributed to managed grazing which included rest periods to re- duce selective grazing pressure on the little bluestem. Although absolute grass cover was greater where tebuthiuron was applied but not followed by prescribed burning, amounts of lit- tle bluestem relative to cover of brownseed paspalum complex dif- N0 herbiCide TebuthiurOn (2.2 kg/ha) fered little from that of untreated Year Unburned Burned Unburned Burned pastures‘ The ratio of little blue' stem to brownseed paspalum cov- 1981 4 12* 12 17* er was greater for three growing 1982 11 29* 8 30* seasons after burning pastures 1983 12 17* 11 12 which had not been chemically Q1984 12 16 13 21* treated. The proportion of little bluestem was increased in all years *Significantly different (P$0.05) from mean of unburned pasture within the respective treat- of evaluation from 1981 through ment based on t-test. 11 1984, except in 1983 where pas- tures treated with 2.2 kg/ha of tebuthiuron were burned in 1981, compared to chemically-treated but unburned pastures. These data indicate that prescribed burning can be used t0 increase the pres- ence of little bluestem on these sites. Cattle Performance and Diets Following Tebuthiuron Application Forage response differences were expressed in livestock per- formance, using weight gains of steers as the criterion (Scifres et al. 1981b), following tebuthiuron ap- plication in 1977 and 1978. By the first fall after application of tebuthiuron in 1977, average daily steer gains, total daily steer gains, and days available grazing were increased on pastures treated with 2.2 kg/ha of tebuthiuron, com- pared to untreated pastures (Table 9). This improvement was main- tained through the first 3 years after tebuthiuron application when the measurements were discon- tinued. In contrast, average daily steer gains and total daily steer gains were negative and less on treated than on untreated pastures during the fall after tebuthiuron applica- tion at 2.2 kg/ha in the spring 1978 (Table 10). Application of 4.4 kg/ha of the herbicide extended the nega- tive effects on livestock perform- ance through the second growing season after treatment. However, animal performance responded positively during the second grow- 1ng season. The favorable response to tebuthiuron application in 1977 can be linked to several important char- acteristics of the oak woodland. First, the woodland had a younger age structure of trees compared to the 1978 study site. Fall standing crops from untreated pastures were five to seven times greater on the younger woodland site treated in 1977 than on the mature wood- land treated in 1978. Therefore, there was a good stand of residual herbage which responded quickly to herbicide treatment compared to the mature woodland. Improved performance of steers grazing tebuthiuron-treated pas- tures in the younger oak woodland can be related to greater stability of the grass stand when subjected to grazing pressure. The steers were able to select diets higher in crude protein the fall and summer follow- ing tebuthiuron application than on the untreated pastures. Ani- mals grazing the untreated pas- tures were unable to select diets having crude protein content above maintenance requirements during the fall after treatment and subsequently lost weight. The greater steer-day/ha capacityw was attributed primarily to greater herbaceous standing crop and more reliance on browse to sustain nutrient requirements. Browse comprised 26 to 45 percent and 4 to 23 percent of the cattle diets at the end of the seasonal grazing trials in the untreated and treated pas- tures, respectively. This resulted in a general trend for reduced caloric (IVDOM) value of the diet and probably reduced forage intake on untreated pastures when compared to treated pastures. En- hanced individual animal perform- ance of steers grazing tebuthiuron- treated pastures can be attributed to higher ad libitum diet quality and greater nutritional stability fur- nished by the pastures. Steer- days/ha capacity of the pastures was primarily a function of initial standing crop and growth rate of herbage as mediated by browse consumption. Particularly important is the greater overall performance of the steers in the untreated pastures during the spring trial on the area treated in 1977. Individual animal performance was essentially the same, yet caloric content was lower and crude protein content was higher in diets of steers grazing Table 9. Dietary composition, quality, animal performance, and forage supply for three seasonal grazing trials after aerial application of tebuthiuron pellets at 2.2 kg/ha to Post Oak Savanna on May 9, 1977, near College Station, Texas Fall1977 Summer1978 Spring1979 Untreated Tebuthiuron Untreated Tebuthiuron Untreated Tebuthiuron Variable Begin‘ End Begin End Begin End Begin End Begin End Begin End Diet composition (%) G rass 83 54 90 76 81 61 99 79 74 46 91 53 Forb 10 1 4 1 10 12 0 16 22 28 8 43 Browse 7 45 6 23 9 27 1 5 4 26 1 4 Diet quality (%) IVDOM2 54 47 53 46 60 49 63 52 57 58 63 64 Crude protein 7.9 6.8 10.0 7.2 8.0 7.2 10.0 7.8 11.3 9.8 10.0 7.8 Animal performance (kg) Avg. daily gain — .01 .35 .35 .60 .63 .58 Gain/ha/day — .21 1.51 1.80 2.76 3.12 2.32 Forage supply Initial standing crop 1,400 1,150 1,100 2,750 350 400 Steer-days/ha 89 61 81 132 59 44 lRefers to beginning and end of trials which generally lasted 10 days. 2In vitro digestible organic matter content. 12 Vi‘ Spring 1980 2.2 4.4 End Begin End Begin End 85 24 88 86 94 83 11 28 10 13 4 48 2 62 48 61 58 61 57 13.4 10.4 14.5 11.2 15.9 13.0 .37 .32 .34 .65 .54 .55 473 1,191 1,363 53 82 85 and forage supply for three seasonal grazing trials after aerial application of tebuthiuron pellets , near College Station, Texas Fall 1978 Summer 1979 2.2 4.4 2.2 4.4 Begin End Begin End Begin End Begin End Begin End Begin End Begin 83 7 10 55 55 61 53 63 55 65 54 11.1 12.3 10.5 7.4 12.4 10.4 13.5 10.4 — .34 — .99 .25 — .11 — .57 —-1.55 .38 .29 — .07 149 183 224 485 141 24 19 36 36 28 quality, animal performance, 59 9.8 — .01 — .04 29 ‘l. Table 10. Dietary composition, Grass Forb Browse IVDOM Crude protein Avg. daily gain (ADC) Gain/ha/day Initial standing crop 221 Steer-days/ha at 0, 2.2 or 4.4 kg/ha to Post Oak Savanna on May 7, 1978 Variable Diet compostion (%) Diet quality (%) Animal performance (kg) Forage supply (kg/ha) untreated pastures. The only logi- cal explanation for this difference relates to the potential dietary role of browse during spring allowing animals to selectively maintain nu- trient intake when herbaceous standing crops are low. Oaks and yaupon, the principal browse species in the pastures, have average in vitro (IVDOM) and crude protein values of 60 to 69 percent and 12 to 16 percent in April, respectively (Tables 11 and 12). These data indicate that com- plete treatment of a pasture would reduce the animal's degree of flexi- bility in selecting forage species to facilitate stability of nutrient in- take. Therefore, the need for pat- terning brush treatments for wild- life habitat should be extended to the need for enhancing livestock selectivity of nutrients on land- scapes. Animal performance data from the mature oak woodland indi- cated that the acute effects of tebuthiuron application were largely caused by reduced standing crop of herbaceous forage and elimination of alternative browse species needed to sustain nutrient intake of the animals. Initial herba- ceous standing crops in the fall following treatment in the spring were similar between untreated and tebuthiuron-treated pastures. However, caloric value of diets for animals grazing the tebuthiuron- treated pastures was lower than for animals on untreated pastures. Apparently the steers had to move onto residual browse much quicker in the tebuthiuron-treated pas- tures which drastically reduced their caloric intake. Only herbicide-resistant woody species with average IVDOM and crude protein contents of 46 to 53 percent and 7.5 to 10 percent, re- spectively, were available during fall after treatment (Tables 11 and 12). The decline in steer-days/ha of grazing with increasing rate of tebuthiuron application indicated that the animals were depleting the herbage supply more rapidly and depending on lower quality residu- al browse in fall than on "brush" pastures. Animal performance was similar in the fall trials of 1977 and 1978 13 and, depending on age structure of the woodland, positive animal per- formance, or acute weight loss, can be extended based 0n characteris- tics of the brush stand treated with tebuthiuron. Animal performance was depressed during the summer 1979 following application of tebuthiuron in spring of 1978, with acute weight loss by steers grazing pastures treated with 4 kg/ha. Analysis of diet composition and quality did not explain the weight losses. However, available herbage apparently was still suppressed in pastures treated with 4 kg/ha of the herbicide causing animals to seek a severely reduced browse reserve. Diet quality data indicated that those animals in pastures treated with 4 kg/ha of tebuthiuron could select alternative diets and sustain nutrient concentration in summer but because of restricted supply could not sustain daily intake. This supports the need to provide cattle with access to untreated areas to buffer against loss of browse as a nutritional reserve. Animal performance differences between treated and untreated pastures were minimal by spring 1980 in the mature oak woodland. Individual animal performance and gain/ha-day were 50 and 20 percent less on spring grazed ma- ture oak woodlands treated with tebuthiuron, compared to younger woodland sites which had been treated. This indicated that expected benefits are delayed ap- proximately 2 years on mature compared to young oak woodlands treated with tebuthiuron. The more rapid positive response in animal performance during the summer 1979 on pastures treated with 2 kg/ha of tebuthiuron pro- vided further evidence of the need to maintain a residual browse supply. Cattle preferred to graze native grassland dominated by little blue- stem and brownseed paspalum and treated with 0.5, 1, or 2 kg/ha of tebuthiuron over adjacent un- treated plots (Scifres et al. 1983). Moreover, cattle usually grazed on plots treated with 1 or 2 kg/ha of tebuthiuron longer and more often than on plots treated with the same rates of 2,4-D [(2,4-dichlorophe— 14 noxy) acetic acid] or picloram sprays. The apparent preference was observed in summer and fall after herbicide application in spring, but was not observed the following growing season. These Table 11. In vitro digestible organic matter (%) content of available terminal 10 cm current year's leaves and stems of major browse sprouts growing on a mechan- ically cleared Tabor fine sandy loam soil of Post Oak Savanna near College Station, Texas, in 1977 and 1978 (each value represents 20 grab samples from 10 plants of each species) Sampling date (1977-78) Plant Species part 12/22 2/26 4/8 6/18 8/21 10/7 Post oak Leaf 46 — 6O 55 45 46 Stem 31 35 58 43 29 31 Blackjack oak Leaf 48 — 60 44 38 41 Stem 29 35 51 4O 30 22 Water oak Leaf 45 49 46 47 44 42 Stem 32 33 38 40 30 29 Winged elm Leaf — — 56 56 54 53 Stem 26 3O 4O 35 33 25 Yaupon Leaf 53 59 69 54 48 53 Stem 29 32 38 38 25 3O Gum bumelia Leaf — — 56 48 49 44 Stem 29 26 46 47 29 24 Willow baccharis Leaf 62 69 64 57 54 50 Stem 48 52 51 46 44 45 Sparkleberry Leaf 44 50 48 43 63 44 Stem 19 26 34 25 28 20 Buckbrush Leaf 56 — 63 66 64 44 Stem 23 24 45 25 29 25 Table 12. Crude protein (%) content of available terminal 10 cm current year's leaves and stems of major browse sprouts growing on a mechanically cleared Tabor fine sandy loam soil of the Post Oak Savanna near College Station, Texas, in 1977 and 1978 (each value represents 20 grab samples from 10 plants of each species) Sampling date (1977-78) Plant Species part 12/22 2/26 4/8 6/18 8/21 10/7 Post oak Leaf 7.5 - 16.7 10.8 8.8 8.5 Stem 5.2 5.2 11.4 7.2 4.0 3.0 Blackjack oak Leaf 5.3 — 16.8 8.6 7.8 8.3 Stem 4.0 3.3 9.3 9.4 3.5 3.2 Water oak Leaf 10.5 11.4 16.3 10.2 8.1 10.3 Stem 5.2 4.6 8.0 5.0 3.6 3.5 Winged elm Leaf — - 17.5 9.8 8.6 9.2 Stem 6.0 5.5 6.9 3.4 4.2 5.0 Yaupon Leaf 14.1 8.6 12.7 8.0 6.6 7.5 Stem 1.7 3.8 4.4 5.6 3.9 3.8 Gum bumelia Leaf — — 16.8 8.6 7.8 8.3 Stern 5.4 6.2 11.6 9.4 5.6 5.6 Willow baccharis Leaf 11.5 10.5 15.2 8.8 8.6 11.0 Stem 5.2 5.0 6.7 5.0 4.3 5.6 Sparkleberry Leaf 8.8 7.1 15.1 7.8 8.7 10.0 Stem 4.1 3.7 8.3 3.9 4.0 8.3 Buckbrush Leaf 13.3 - 16.4 7.0 6.5 14.9 Stem 3.6 3.7 5.5 2.5 3.6 4.5 ‘i observations were later confirmed when tillers of brownseed pas- ‘Qgpalum were permanently marked in pastures receiving partial treat- ment with tebuthiuron at 2 kg/ha. Tiller height reduction was monitored before and after grazing on a treated and untreated grass- land community within a pasture of a 15-pasture, 1-herd short dura- tion grazing system. Cows re- moved 5.2 to 9.2 cm more height from tillers growing in treated than untreated grasslands from August through November (Table 13). There were no observable dif- ferences in tiller use during winter. Approximately 25 percent of the marked tillers in the study over- wintered in the untreated grass- lands while no tillers survived the extremely cold winter on the sites treated with tebuthiuron. This ap- pears to be related to loss of insular properties by the grass bunches and reduced fall tiller production by heavily grazed plants. Masters and Scifres (1984) inves- tigated the potential influence of tebuthiuron applications on nutri- tional attributes of several grasses. The in vitro digestible organic mat- ter concentrations of leaves of little bluestem, bahiagrass, Bell rhodes- grass, or green sprangletop were not altered by applications of 1.1 or 2.2 kg/ha (active ingredient) of tebuthiuron. Leaf water concentra- tions of bahiagrass, green spran- gletop, or little bluestem were not consistently altered by application of tebuthiuron. However, applica- tion of 1.1 or 2.2 kg/ha of tebuthiuron to seeded stands or to native little bluestem increased fol- iar crude protein concentrations. Applications of 0.125, 0.188, or 0.25 parts per million of tebuthiuron in aqueous solutions to pots contain- ing grasses in the greenhouse sig- nificantly increased foliar crude protein concentrations, compared to untreated plants. Crude protein concentrations were increased on- ly during the growing season of application in the native stand of little bluestem. These results sug- gested application of tebuthiuron for brush control may enhance crude protein concentrations while not affecting in vitro digestible or- ganic matter. Post-burn Diet Selection by Cattle Diet quality and quantity of steers grazing during the spring and fall following burning were contrasted in 1981 on the oak woodland site treated with tebuthiuron in 1978 to determine livestock responses to mainte- nance burns (Table 14). Surprising- ly, burning did not enhance diet quality during late spring 9O days following burning. Diet crude pro- tein was lower for steers on the burned pastures in spring. There was a trend for diet IVDOM to be higher on burned pastures in spring and fall following burning. Table 13. Height reduction brownseed paspalum tillers in untreated and tebuthiuron-treated grassland communities of a pasture six months post- treatment in a 15-pasture, 1-herd (16 pregnant cows) rotational grazing system, August 1984 to January 1985 near College Station, Texas Height reduction Grazing period Treatmentl cm % Aug. 24-30 Tebuthiuron 12.6 52 None 5.0* 35 Sept. 26-Oct. 4 Tebuthiuron 15.7 70 None 4.5* 27 Nov. 15-22 Tebuthiuron 6.6 46 ___ None 1.4* 12 ‘Dec. 26-Jan. 6 Tebuthiuron 1.9 18 None 2.3 21 ‘Tebuthiuron aerially applied at 2.2 kg/ha in May 1977. *Significant difference between treatments (PsOS) During spring the steers selected diets similar in species composition (Table 15). However, amount of live leaf tissue was higher and live stem and seedhead consumption was lower in diets from the burned pastures. Brownseed paspalum was the primary seed contributor to the diets. Apparently, greater seed consumption increased rela- tive crude protein levels in the diets of steers grazing unburned pas- tures. Greater leaf blade consump- tion probably explains the trend for higher IVDOM in diets selected from the burned pastures during spring. Burning resulted in greater grass and less forb consumption during the fall after burning (Table 15). This probably explains the higher crude protein and lower IVDOM contents of steer diets from the unburned than from burned pas- tures. Diets of cattle grazing burned pastures in the fall con- tained more live leaf tissue and a lower proportion of seedheads than cattle grazing the unburned pastures. Winter burning may not im- prove livestock performance in the spring but would allow steers or lactating cows to select diets that exceed maintenance requirements in fall. Thus, producers could cap- ture gains in steers over a longer Table 14. Crude protein (CP) and in vitro digestible organic matter (IVDOM) of esophageally fistulated steers grazing tebuthiuron-treated pastures in the Post Oak Savanna near College Station, Texas, during spring and fall following a late winter burn in February 1981 Nutritent content (%) CP IVDOM (Mean i (Mean i Treatment S.E.)1 S.E.) Spring 1981 Unburned 10.8 i .54 56.3 i 1.20 Burned 8.2 i .45* 58.0 i 1.08 Fall 1981 Unburned 8.4i .37 52.6i1.00 Burned 7.7i .27 57.4 i 1.00* lAverage values and associated standard errors. *Significantly different from unburned (Ps0.05). 15 period and wean heavier spring calves or increase conception of fall calving cows. Probably, it would be wise to provide a protein supple- ment (e. g. low cost molasses/urea source) during late summer and into fall if precipitation does not stimulate fall forb production fol- lowing burning. A part of this research was di- rected toward determining how tebuthiuron shapes the plant com- munity and interacts with burning to affect nutritional stability of the pasture. Specifically, the question becomes: how does the presence of browse interact with burning to affect how an animal can sustain nutrient intake? A series of graze-out trials were conducted in May, August, and Ianuary after burning in February 1984 on the pastures treated with tebuthiuron in 1977. The tebuthiuron-treated pastures pro- vided an excellent stand of grass with little available browse, while adjacent bulldozed pastures had abundant resprouts of shrubs, ma- ture trees, and relatively good her- baceous stands. Dietary IVDOM of cattle was not affected by plant stand composi- tion differences a year after burn- ing if grazing pressure was not heavy (Table 16). However, when grazing pressure was increased, animals switched to browse in the bulldozed pastures and main- tained nutrient concentration at a higher level than in tebuthiuron- treated pastures, except in the hot dry part of summer. Browse in summer is very low in IVDOM (Table 11). Interestingly, the same can be said for crude protein con- tent of cattle diets except under moderate grazing. Cattle selected diets higher in crude protein dur- ing August on burned pastures previously treated with tebuthiuron compared to bull- dozed and burned pastures. This is attributed to higher browse con- sumption on tebuthiuron-treated versus bulldozed pastures during the hot dry period of the year (Fig- ure 1), primarily because of greater consumption of willow baccharis and water oak. When subjected to excessive grazing pressures, the burned pas- 16 tures previously treated with tebuthiuron offered fewer oppor- tunities for the steers to select al- ternative diets. This resulted in less nutritional stability of cattle diets from tebuthiuron-treated pas- tures. Again, it is apparent that maintaining diverse habitats through patterning of treatments is critical for stabilizing seasonal nu- trient intake of cattle. Influence on Wildlife Habitat Attributes Based on measurements in Au-J gust 1985, tebuthiuron application alone did not significantly alter av- erage distance to screening closure (Table 17). Development of the understory shrub cover essentially . . replaced the screen provided by W Table 15. Composition of diets of esophageally fistulated steers grazing pastures treated with tebuthiuron in 1977 during the spring following a late winter burn in 1981 near College Station, Texas Food group Grass Forb Browse Plant part Unburned Burned Unburned Burned Unburned Burned Spring 1981 Live leaf 30.8 54.0* 6.2 6.3 0 0 Dead leaf 4.8 3.8 — — 1.2 2.0 Live stem 33.5 18.3* 1.0 1.0 0 0 Dead stem 1.2 0.8 0.3 0.8 0 0 Reproductive 18.3 10.3* 3.0 2.5 0 0 Total 88.3 87.4 10.5 10.6 1 2 2.0 Fall 1981 Live leaf 23.8 53.1 * 2.3 0.5 0.5 0.6 Dead leaf 18.9 12.9 1.4 0 0.3 0 Live stem 16.2 15.1 2.6 1.8 0.1 0 Dead stem 5.4 2.9 1.8 0.3 0 0 Reproductive 19.0 11.0* 5.5 1.7* 0 0 Total 84.2 95.1* 13.6 4.3* 2.2 0.6 *Significant differences exist between treatments by food group and plant part (P<.05). Table 16. In vitro digestible organic matter (IVDOM) and crude protein (CP) content as percentages of diets selected by cattle subjected to a graze-out regime on pastures treated with 2.2 kg/ha of tebuthiuron in 1977 or bulldozed the growing season following burning in February 1984 near College Station,Texas Nutrient (%) by grazing pressure IVDOM CP Treatment Moderate Heavy Severe Moderate Heavy Severe May Tebuthiuron/burn 56 51* 56* 8.9 10.3* 10.1* Bulldoze/burn 56 58 54 9.5 13.1 11.5 August Tebuthiuron/burn 57 44 44* 9.1* 5.5* 5.6* Bulldoze/burn 57 46 41 7.8 6.6 7.9 January ~\ Tebuthiuron/burn 46 46 44* 6.7 5.4 5.7 Bulldoze/burn 45 50 47 6.9 6.1 6.6 *Significant differences exist between treatments by food group and plant part (P<.05). Percent Browse Found in Diet 30 18!C] JO IUSDJGd 1S Tebuthiuron-Burn s 45 - 30 - ISQC] JO IUSDJBd 15 -— May Figure 1. Percent browse in diets of cattle subjected to a series of raze-out trials the year following burning in the winter 1984 of pastures bulldozed or aerially treated with tebuthiuron at 2.2 k / in May 1977. 1 the original woody cover. Pre- scribed burning following tebuthiuron application increased the distance to screening closure by reducing canopy cover and density of species such as American beautyberry. However, the greatest distance to screening closure was only 21 rn. Subsequent burns likely would increase the distance to screening closure by continuing to diminish understory shrub cover. Thus, width of treated strips should be considered in treatment design. Table 17. Average distance (m) to screening closure in August 1985 after application of tebuthiuron in May1978 or where herbicide treatment was fol- lowed by prescribed burning in the late winters of 1981 and 1984 near Col- lege Station, Texas Tebuthiuron Bumed1 rate iii (kg/ha) Yes No 0 12 a 13 ab 2.2 11 a 17 bc 4.4 14 ab 21 c 1 Means followed by the same letter are not significantly different (Ps0.05) according to Student-Newman-Keul's test. Tebuthiuron had little direct ef- fect on forb production by the third growing season after application (Table 5), and subsequent burning in the winter can promote forb standing crops. Therefore, there is no indication that the tebuthiuron- burning sequence reduces quality of habitat for deer if the treatments are applied in an appropriate pat- tern. In addition, several beneficial attributes can be derived from her- bicide-burn sequences. Brush re- moval opens thick cover that hin- ders hunters in pursuit of game. Game can be seen more easily, thereby possibly increasing the marketability of hunting leases. Al- so, subsequent burning of grass- lands can increase availability of seeds and insects to granivorous and insectivorous species such as bobwhite quail (Koerth et al. 1986). These experiments were de- signed so that untreated strips were alternated with treated strips. 18 Given the rolling terrain over much of the Post Oak Savanna, strip treatment provides an acceptable alternative for most brush manage- ment programs. It is suggested that treated strips be alternated with untreated strips to remove some of the woody canopy cover to in- crease herbaceous production while still allowing deer easy ac- cess to brushy areas for browsing and/or escape and thermal cover. Treated strips no more than 325 m wide should not limit use of the entire clearing by deer. Untreated strips, at least 80 m wide, should _ allow deer to find adequate screen- ing cover even when deciduous species are defoliated. Such a pat- tern would result in no more than 80 percent of a pasture being treated with herbicide. Untreated strips also should be left along drainageways, around watering facilities, and adjacent to cultivated fields to allow maximum use of these areas by wildlife. Senzota (1985) evaluated the re- sponse of small mammals to the treatments initiated in 1978 from fall 1982 to fall 1983. At least six species of small mammals were present during the study period, but only cotton rats and wood rats occurred in numbers adequate for evaluating their responses to treat- ment. Reduction of shrub canopy cover by burning was followed by a sharp reduction in the abundance of wood rats. Reduction of herba- ceous cover reduced cotton rats for most of the year following the burns. As the grass-dominated herba- ceous cover was restored, the cot- . ton rat population returned to pre- burn densities (Senzota 1985). Be- cause significant shrub cover was not established during the year fol- lowing burning, wood rats did not use the burned areas for the year following treatment. Senzota (1985) concluded that annual burn- ing would drastically reduce wood rat populations. However, fre- quent burning would likely induce cyclic use patterns of treated areas by cotton rats. He further hy- pothesized that a prescribed burn- ing frequency that promoted grass cover would encourage an increase in cotton rat populations. Influence of Tebuthiuron/ Prescribed Burning on Watershed Attributes Terminal infiltration rates and sediment production 3 years after aerial application of tebuthiuron at 2.2 kg/ ha differed little from values for untreated (wooded) areas (Lloyd-Reilley et al. 1984). Pre- scribed burning in the winter (De- cember-February) temporarily de- creased infiltration rates and in- creased sediment production. Infil- tration rates equilibrated among brush management treatments with reinstatement of the herba- ceous cover within 6 months after burning. Sediment production was gener- ally greater from burned than un- burned plots after 5.5 months, but the absolute amount of sediment produced on the near-level (1-3 percent slope) fine sandy loam sites was not great, regardless of treatment. Moreover, sediment production from burned sites was not significantly different from that of untreated sites 1 year after burn- ing. The brush management treat- ments had no effect on nitrate con- centrations in runoff. However, in one of two experiments, total unfil- tered nitrogen and phosphorus contents in runoff were slightly greater during the growing season following burning than from un- burned sites. Integration of Prescribed Burning with Tebuthiuron Applications Tebuthiuron effectively con- trolled many of the major woody species on rangeland dominated by oaks and mixed hardwoods. However, several species of shrubs tolerated the treatment and in- creased in abundance after the overstory of oaks was removed. The increase in abundance of vines was spectacular following tebuthi- uron application. For example, saw greenbrier rapidly grew up and in- to the aerial portions of many of the . dead oak trees. This growth was s ' extensive that it essentially re- placed the original oak canopies until the trees deteriorated. Compared t0 responses of her- baceous vegetation following ap- "\lplication of foliar sprays for woody plant control, vegetation changes following application of tebuthi- uron lag for approximately one growing season, depending on rainfall. For example, application of foliar sprays for brush manage- . ment may remove the woody canopies within 3O days (Scifres 1980), which allows the cover and standing crop of the herbaceous understory to increase by fall of the first growing season. In contrast, maximum herbaceous production may not occur until the second growing season after tebuthiuron application. As a consequence, fine fuel (herbaceous plants) of ade- quate load for prescribed burning is not accumulated until the fall of the second year following tebuthi- uron application. Fuel continuity may not be ade- quate to carry an effective fire until the third fall following application of the herbicide. By that time, vines and shrubs that tolerated the her- bicide treatment may have become the limiting factor to herbage pro- duction. During this period, post and blackjack oak trees killed by the herbicide progressively de- teriorate. Wind storms may re- move essentially all except the pri- mary branches from the trees, ad- ding a considerable amount of coarse fuel to the herbaceous layer. Therefore, the data suggested that it is critical to plan the first burn for the winter in the third year follow- ing tebuthiuron application. Pastures were burned when the air temperature was greater than 16 °C, relative humidity less than 50 percent, and the wind speed was 13 to 20 kilometers per hour (kph). Under these conditions, standing fine fuel water content was normally less than 20 percent. However, the logs and large branches on the soil surface were wet on the underside, and water content often averaged 60 percent for pieces 10 cm or larger in diameter. \ The first burn may be relatively cool and spotty because of the pres- ence of surviving brush plants and the relatively wet, fallen wood from dead oak trees that litter the surface. Little of this wood, limited primarily to those pieces 5 cm or smaller in diameter, may be re- moved by the first burn, except where accumulated piles ignite. Accumulations of the fallen wood restrict fine fuel development and provide discontinuities that may a prevent their ignition. Ignition of the piles results in hot local fires that delay subsequent develop- ment of herbaceous stands. Given annual average rainfall, a second burn may be best timed for application during the second or third winter following the first pre- scribed burn. The first prescribed burn in this research reduced the stature of surviving woody plants, removed some of the fallen debris, and generally promoted fuel con- tinuity. The second burn removed as much as 5O percent of the re- maining debris, removed the tops of many of the surviving woody plants, and removed vines such as saw greenbrier to ground line. Bo- tanical composition following the second burn was characterized by relatively large proportions of little bluestem and other species favored by burning. Prescribed burns may be applied at 3-year intervals fol- lowing the second burning and the grass sward progressively im- proved. Development of a fine fuel load of adequate continuity to carry an effective burn necessitated defer- ment from grazing in this study. Cattle usually were removed in late August-early September (depend- ing primarily on August rainfall) to allow herbage growth in the fall. In most years, this deferment allowed accumulation of 3,000 kg/ha or more fine fuel, depending on the shrub cover. Burns were applied in February and pastures were not grazed in most years until mid- April when the desirable grasses were of relatively high vigor. Economic Comparison of Brush Management Treatments Scifres (1987) projected the eco- nomic performance of tebuthiuron alone and tebuthiuron followed by prescribed burning on pastures ini- tially treated in 1977 (hereafter re- ferred to as moderate brush cover) and in 1978 (heavy brush cover) with 2.2 kg/ha of tebuthiuron. The herbicide application was assumed to cover the entire management unit (i.e. not patterned). Carrying capacities were projected over the expected lives of the treatments based on trends in vegetation change from 1977-78 through 1986. Estimated costs of treatment were $110.25/ha for tebuthiuron application, $10/ha for the first pre- scribed burn, and $5/ha for subse- quent burns. Purchase prices were $650 for cows and $1,250 for bulls (assumed ratio of 1 bull/19 cows). Variable costs for annual mainte- nance was $100/AU for pastures with heavy initial brush cover and $80/AU for the pastures with mod- erate cover. Selling price of calves over the analysis period was $1.45/kg. No interest charges were associated with the investment capital. The brush management projects were considered as poten- tial alternative investments to plac- ing capital in interest accruing ac- counts. Economic comparisons were based on estimated cash flows, in- ternal rates of return, and net pre- sent values (Scifres 1987). A 10 per- cent discount rate was arbitrarily selected for comparing alterna- tives. When the net present value of treatment is 0, the project has paid all costs and generated a 10 percent return on the investment. Application of 2.2 kg/ha of tebuthiuron to the moderate brush cover was projected to have a 16- year treatment life and to yield 9 kg/ha more beef each year of the expected treatment life than on ad- jacent untreated pastures (Scifres 1987). The herbicide application was projected to generate a 8.2 percent internal rate of return. In contrast, the internal rate of return following application of tebuthi- uron to the mature oak woodland (1978 site) was negative over the expected 12-year treatment life. Accumulated cash was estimated at $-14.13/ha following treatment of the heavy brush cover compared to $147.02/ha after tebuthiuron ap- plication to the moderate woody 19 cover. The difference in economic performance was attributed to (1) the reduced performance of live- stock the year after treatment of the heavy brush cover and (2) the rapid dominance of the treated pastures by previously subordinate vines and shrubs. The application of prescribed burns at 2, 4, and 7 years after application of tebuthiuron to the moderate brush cover increased the internal rate of return by 2.7 percent to 10.9 percent, compared to application of the herbicide but with no prescribed burning (Scifres 1987). Prescribed burning ex- tended the effective treatment life to 2O years, compared to 16 years without burning, and increased the estimated additional beef pro- duced to 13.9 kg/ha/year. Prescribed burning at 3 and 6 years after application of tebuthi- uron at 2.2 kg/ha to the heavy brush cover resulted in an es- timated 6.6 percent internal rate of return, compared to a negative in- ternal rate of return where her- bicide application was not followed by burning (Scifres 1987). The pre- scribed burns extended the ex- pected treatment life from 12 to 17 years. The positive influence of prescribed burning following te- buthiuron application to the heavy brush cover was attributed to sup- pression of vines and shrubs re- leased by the herbicide treatment. Observations in 1986, 10 grow- Ecological,Economic, and Manatee ent Implications Experiments monitored continu- ously for 9 to 1O growing seasons allow several conclusions about the use of tebuthiuron for manage- ment of oak-mixed hardwood stands. These conclusions apply to late winter-early spring applica- tions of the herbicide. 1. Tebuthiuron pellets aerially applied at 2.2 kgflia (active ingredient) effectively control post oak, blackjack oak, water oak, and associated hard-to- kill species such as yaupon and winged elm. Control, ex- pressed as canopy reduction and killing of plants, is usual- ly not fully expressed until the second growing season following herbicide applica- tion in the spring. 2. Vines and shrubs not con- trolled by the herbicide may increase dramatically on some sites, becoming a man- agement problem by the third growing season after tebuthiuron application. In addition, species not occur- ring prior to tebuthiuron ap- 2O plication or present in small amounts may also increase in importance. These secondary woody stands may be sup- pressed by prescribed burn- ing with headfires during late winter; burning a second time within 2 or 3 years of the first burn will likely be required for most sites to maintain shrub suppression. 3. Grass production usually is not increased the growing season following application of 2.2 kg/ha of tebuthiuron pellets. This lag in grass re- sponse is related to the time required for maximum brush control to occur. Application of 4.4 kg/ha of the herbicide may suppress grass produc- tion in localized areas through the second growing season after application. Pre- scribed burning during the winter after the second or third growing season follow- ing tebuthiuron application will increase grass produc- tion, compared to areas ing seasons after application of the tebuthiuron, indicated that pre- scribed burning at approximately " 3-year intervals will likely per- i petuate the positive benefits of her- bicide treatment for an additional 10 years. However, the understory shrubs rapidly thickened following the burn in 1984 wherejtebuthiuron had been applied to the heavy brush cover in 1978. The increase in shrub cover and associated re- ductions in amount and continuity of fine fuel mean that prescribed burning will no longer be effective. Thus, chemical or mechanical brush management to reduce the cover of shrubs will likely be re- quired to reinstate forage produc- tion on the pastures. treated with the herbicide and not burned. 4. Control of woody plants with tebuthiuron increases the proportion of grasses of good- to-excellent value for grazing. This may be largely attributed to the increase the amount of species such as little bluestem in the grass stands. Pre- scribed burning amplifies and accelerates this shift in species composition. 5. Forb standing crops may not be affected during the first growing season following ap- plication of tebuthiuron pel- lets at 2.2 kg/ha but may be reduced during the second and third growing seasons. Prescribed burning during the winter will enhance rein- statement of forb popula- tions. 6. Steer gains may be reduced for the first growing season following application of .,._ tebuthiuron to heavy brush“! cover. This is attributed to the slow response of grasses to treatment and the reduction of available browse. The negative effect on animal per- formance may not occur fol- lowing treatment of moderate brush cover where some grass production occurs even though brush control is de- layed. Maintenance of habitat diversity (patterns, rates of treatments, timing of treat- ments, etc.) is critical for cattle to stabilize nutrient intake. . Tebuthiuron application may cause grasses to be preferred for grazing by cattle during the growing season following application. Special attention should be given to this possi- bility where the herbicide is applied in a pattern, such as for wildlife habitat. Reasons for the preference have not been discerned, but crude protein content of grass leaves may be increased for the growing season following tebuthiuron application. These effects are not detect- able during the second grow- ing season following applica- tion of the herbicide. . Where white-tailed deer man- agement is a land-use ob- jective, tebuthiuron should be applied in strips, probably no more than 325 m in width, and alternated with untreated strips to treat no more than 80 percent of the landscape. This pattern allows deer easy ac- cess to brush areas for brows- ing and/or escape and ther- mal cover. 9. 10. Application of tebuthiuron followed by burning of near level sandy loam sites only temporarily influenced infil- tration rates and sediment production. However, the po- tential negative effects of burning should be considered in management planning for areas with slopes greater than 3 percent. Estimated internal rates of re- turn from investment in tebuthiuron applications were greater on sites not in- vaded by previously subordi- nate shrubs. Prescribed burn- ing may be used to suppress the negative influence of the shrubs and vines and increase internal rate of return associ- ated with treatment. Literature Cited A.O.A.C. 1970. Official methods of analysis (Ed.). Assoc. of Agr. Chem. Washington, D.C. 832 pp. Cottam, G. and I.T. Curtis. 1956. The use of distance \ ? measures in phytosociological sampling. Ecology 37:451- . 460 Darrow, R.A. and W.G. McCully. 1959. Brush control and range improvement in the post oak-blackjack oak area of Texas. Texas Agr. Exp. Sta. B-942. 16 pp. Gould, F.W. 1975. Texas plants: A checklist and ecological summary. Texas Agr. Exp. Sta. MP-585 (Rev.). 121 pp. Gould, F.W. and T. W. Box. 1965. Grasses of the Texas Coastal Bend. Texas A&M Univ. Press, College Station, Texas. 186 PP- I-Ioffman, G.O., I.D. Rodgers, B.I. Ragsdale, and R.V. Miller. 1970. Know your grasses. Texas Agr. Ext. Serv. B-182. 47 PP- Kirby, D.R. and I.W. Stuth. 1981. Brush management influ- ences the nutritive content of cattle diets in east-central Texas. I. Range Manage. 35:431-433. Kirby, D.R. and I.W. Stuth. 1982. Botanical composition of cattle diets grazing brush managed pastures in east- central Texas. I. Range Manage. 35:434-436. Koerth, B.H., I.L. Mutz, and I.C. Segers. 1986. Availability of bobwhite foods after burning Pan American balsam- scale. Wildl. Soc. Bull. 14:146-150. Lloyd-Reilley, I., C.I. Scifres, and W.H. Blackburn. 1984. Hydrologic impacts of a tebuthiuron-prescribed burning management system on Post Oak Savannah watersheds, Texas. Agric. Ecosystems and Environ. 11:213-224. Lopes, E.A. and I.W. Stuth. 1984. Dietary selection and nutrition of Spanish goats as influenced by brush man- agement. I. Range Manage. 37:554-560. 21 Masters, R.A. and C.]. Scifres. 1984. Forage quality re- sponses of selected grasses to tebuthiuron. I. Range Manage. 37:8387. Meyer, R.E., R.W. Bovey, and ].R. Baur. 1978. Control of an oak (Quercus) complex with herbicide granules. Weed Sci. 26:444-453. Scifres, C.I. 1980. Brush management: Principles and prac- tices for Texas and the Southwest. Texas A&M Univ. Press, College Station, Texas. 360 pp. Scifres, C.I. 1987. Economic assessment of tebuthiuron-fire systems for brush management. Weed Technol. 1:22-28. Scifres, C.I. and R.H. Haas. 1974. Vegetation changes in a post oak savannah following woody plant control. Texas Agr. Exp. Sta. MP-1136. 12 pp. Scifres, C.I., I.W. Stuth, and R.W. Bovey. 1981a. Control of oaks and associated woody species on rangeland and tebuthiuron. Weed Sci. 29:270-274. Scifres, C.]., I.R. Scifres, and M.M. Kothmann. 1983. Differ- ential grazing use of herbicide-treated areas by cattle. I. Range Manage. 36:65-69. Acknowledgments The initial phase of this study was conducted cooperatively with Dr. R. W. Bovey. Dr. L. F. Bouse is gratefully acknowledged for aerial application of the herbicide which was supplied by Lilly Research Labs. Those who aided in plot installation, evaluation, and maintenance include Al Rasmussen, Mike Foster, An- dy Crane, Rob Flinn, Iohn Lloyd-Reilley, Ken Parker, David McKown, Ray Angel, and Hugh Aljoe. The efforts of Iulia Scifres in manuscript preparation are appreciated. 22 Scifres, C.I., I.W. Stuth, D.R. Kirby, and R.F. Angell. 1981b. Forage and livestock production following oak control with tebuthiuron. Weed Sci. 29:535-539. ix Senzota, R.B.M. 1985. Effects of prescribed burning on aw small mammal community in Post Oak Savannah, Texas. Ph.D. Diss. Texas A&M Univ., College Station, Texas. 92 PP- Steel, R.G.D. and I.H. Torrie. 1960. Principles and proce- dures of statistics. New York: McGraw-Hill Book Co. 481 PP- "7 Steinert, W.G. and I.F. Stritzke. 1977. Uptake and phytotox- icity of tebuthiuron. Weed Sci. 25:390-395. Stritzke, I.F. 1976. Selective removal of brush by grid place- ment of herbicides. Proc. South. Weed Sci. Soc. 292255 (Abstr.). Tilley, I.M.A. and R.A. Terry. 1963. A two-stage technique for the in vitro digestion of forage crops. I. British Grass- land Congr. 18:104-111. Van Soest, P.I. and R.H. Wine. 1967. Use of detergents in the analysis of fibrous feeds. IV. Determinations of plant cell- wall constituents. I. Assoc. Off. Agr. Chem. 50:50-55. e Appendix A ‘ Scientific Names of Plants and Animals Mentioned in Text \! Common Name Scientific Name Plants American beautyberry Callicarpa americana Bahiagrass Paspalum notatum Bell rhodesg-rass Chloris gayana Black locust Robinia pseudo-acacia Blackjack oak Quercus marilandica Black willow Salix nigra Broomsedge bluestem Brownseed paspalum Buckbrush Bullnettle Cedar elm Chinese elm Chinese tallow Chinaberry Common bennudagrass Common honeylocust Common persimmon Coralberry Dallisgrass Downy hawthorn Eastern redcedar Farkleberry Green sprangletop Gum bumelia Honeylocust Honey mesquite Indiangrass Little bluestem Andropogon virginicus Paspalum plicatulum Symphoriocarpos orbiculatus Cnidoscolus texanus LIlmus crasszfolia lllmus pumila Sapium sebiferum Melia azedarach Cynodon dactylon Gleditsia triacanthos Diospyros virginiania (see buckbrush) Paspalum dilatatum Crataegus mollis Iuniperus virginiana Vaccinium arboreum Leptochloa dubia Bumelia lanuginosa Gleditsia triacanthos Prosopis glandulosa var. glandulosa Sorghastrum nutans Schizachyrium scoparium Common Name Peppervine Poison ivy Post oak Possumhaw Pricklypear Purpletop Red lovegrass Saw greenbrier Smutgrass Southern dewberry Sparkleberry Splitbeard bluestem Sugar hackberry Texas persimmon Texas wintergrass Tree hucklebeny Water oak Western ragweed Willow baccharis Winged elm Yankeeweed Yaupon Bobwhite quail Cotton rat White-tailed deer Wood rat Scientific Name Plants (Continued) Ampelopsis arborea Rhus toxicodendron Quercus stellata var. stellata Ilex decidua Opuntia spp. Tridens flavus Eragrostis secundzflora Smilax bona-nox Sporobolus indicus Rubus trivialis (see farkleberry) Andropogon ternarius Celtis laevigata Diospyros texana Stipa leucotricha Vaccinium arboreum Quercus nigra Ambrosia psilostachya Baccharis salicina LIlmus alata Eupatorium compositzfolium Ilex vomitoria Animals Colinus virginianus Sigmodon hispidus Odocoileus virginianus Neotoma floridana 23 Appendix B Conversion of Metric to English Unitsl Metric English Equivalent 1 pound per acre (lb/A) 1.1 kilograms per hectare (kg/ha) 1 hectare (ha) 2.471 acres 1 kilogram (kg) 2.205 pounds 1 kilometer (km) 0.621 mile 1 meter (m) 3.28 feet 1 centimeter (cm) 0.394 inch lTemperature in degrees centigrade (°C) may be converted to degrees Farenheit (°F) using the relationship (°C >< 9/5) + 32 — °F. 24 [Blank Page in Original Bulletin] ‘ u!’ a? 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