• Desert mule deer use of grazed and ungrazed habitats

      Ragotzkie, K. E.; Bailey, J. A. (Society for Range Management, 1991-09-01)
      We studied use of pastures and habitats in relation to moderate cattle grazing for 19 radio-collared desert mule deer (Odocoileus hemionus crooki) in a southeastern Arizona grass-shrubland. For each deer, use of grazed or ungrazed pastures and habitats in relation to their availability within the deer's home range was tested on a seasonal and annual basis. Deer, especially females during summer, tended to use currently ungrazed portions of their home range and dry wash habitats more than expected. Most deer showed a strong preference for ungrazed dry wash habitats, followed by grazed dry washes and ungrazed uplands. Although deer used grazed uplands less than expected based on availability, deer were still observed frequently in this abundant type. Deer use of currently ungrazed habitats may have been due to absence of cattle or to effects of recent cattle grazing in these habitats. During 2 years of favorable precipitation and forage conditions deer appeared to be adjusted to moderate rest-rotation cattle grazing. Leaving some areas periodically ungrazed might also provide a contingency for deer against impacts of cattle grazing during drought.
    • Diet sample collection by esophageal fistula and rumen evacuation techniques

      Olson, K. C. (Society for Range Management, 1991-09-01)
      Two trials were conducted to compare diet samples collected in the evacuated rumen or through the esophageal fistula. Hypotheses tested were (1) rumen evacuation would not decrease selectivity, (2) being in the rumen during collection would not alter the sample, and (3) both techniques accurately estimated nutritional characteristics of the feed offered. Five steers bifistulated at the esophagus and rumen were used in a grazing and a stall trial. Three collection techniques were used in each trial: rumen collection after evacuation (RC), esophageal collection with the rumen evacuated (ECRE), and esophageal collection with the rumen full (ECRF). Comparison of RC and ECRE assessed the influence of being in the rumen, and ECRE vs ECRF tested selectivity. Hay was sampled before feeding in the stall trial to test hypothesis 3. All samples were analyzed for organic matter (OM), nitrogen (N), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose, and cellulose. In the grazing trial, collection technique affected only ADL (P = 0.05), with ECRE depressed compared to ECRF. Organic matter, N, ADL, and hemicellulose responded (P < 0.05) during the stall trial as follows. Salivary ash contamination depressed OM (P = 0.03) in all collected masticate compared to the feed offered. Rumen collection elevated N (P = 0.04), but esophageal samples and feed were equal. Hemicellulose was depressed slightly (P = 0.01) in all collected masticate. Both techniques elevated ADL (P = 0.001), with RC having a greater effect than ECRF. Both collection techniques should provide satisfactory results in grazing trials if precautions are taken. Comparison across techniques appears appropriate if caution is exercised, particularly concerning N and ADL.
    • Effects of seasonal rest in aboveground biomass for a native grassland of the flood Pampa, Argentina

      Hidalgo, L. G.; Cauhépé, M. A. (Society for Range Management, 1991-09-01)
      Changes in total biomass and botanical composition in a native pasture of the Flooding Pampa in the Salado River Basin (Province of Buenos Aires), under 3 grazing systems: spring-summer rest (November, December, and January); fall rest April, May, and June), and continuous grazing were evaluated from October 1979 to August 1981. A variable stocking rate based on available forage was used. Total aboveground biomass was periodically sampled to ground level and separated into dead and green components. The green biomass was subdivided into individual species. Total aboveground biomass averaged 4,600 +/- 445 kg ha-1 and 3,750 +/- 120 kg ha-1 for the spring-summer rest treatment during the first and second years, respectively. In the same period, warm-season species increased, principally due to an increase in dallisgrass (Paspalum dilatatum Poir.) and bluestem (Bothriochloa laguroides Herter) biomass. Total aboveground biomass yield was 2,000 +/- 170 kg ha-1 during the fall rest treatment, and cool-season species such as Poa spp. and Stipa spp. increased. In general, continuous grazing at a moderate intensity resulted in total aboveground biomass of about 2,000 kg DM ha-1 throughout the experimental period. Contributions of warm-season and cool-season species did not change. Only West Indies smutgrass (Sporobolus indicus (L.) R. Br.) increased under continuous grazing.
    • Forage yield and white-tailed deer diets following live oak control

      Fulbright, T. E.; Garza, A. (Society for Range Management, 1991-09-01)
      Live oak (Quercus virginiana Mill.) competes with herbaceous plants, but provides browse and mast for white-tailed deer (Odocoileus virginianus Zimmerman). We determined the effects of treating live oak with tebuthiuron on yield of herbaceous vegetation and white-tailed deer diets and nutritional indices. In 1982, 259 ha were aerially treated with 2.2 kg/ha active ingredient of tebuthiuron pellets in parallel, alternating treated and untreated strips, each measuring 76 m wide. A second area was treated in 1984. We clipped herbage during June and November 1985-86 within exclosures in treated and untreated strips, and determined chemical and botanical composition of rumen contents and kidney fat index (KFI) from deer killed in the 1982 strip treatment area and a control (untreated) area. Grass yield was 2-4 times higher on treated thin on untreated range. Forb yield was almost 5 times greater on range treated in 1982 than on untreated range, but yield on untreated range and areas treated in 1984 was similar. Deer sampled in the control ares had consumed more forbs than those sampled in the herbicide-stripped area except in fall 1985. The KFI was greater for deer sampled in the control area in fall 1985 and greater for those sampled in the stripped area in fall 1986. Treatment with tebuthiuron in alternating strips increased forage yield for cattle and was apparently not detrimental to KFI of deer.
    • Genetic variances for dry matter yield, nitrogen content, and nitrogen yield in crested wheatgrass-alfalfa mixtures

      Asay, K. H.; Mayland, H. F. (Society for Range Management, 1991-09-01)
      Since its introduction from Asia in the early 1900s, crested wheatgrass [Agropyron cristatum (L.)Gaertner, A. desertorum (Fisch. ex Link) Schultes et al.] has had a major impact on the improvement of western rangelands of North America. Most of the early seedings with this cool-season grass were made as monocultures. Present and projected use of rangelands, however, prescribe that future crested wheatgrass cultivars have the genetic potential to be an effective component in a species complex including other grasses, shrubs, and forbs. The present study was conducted to evaluate the effect of associated alfalfa (Medicago sativa L.) on the performance and genetic variability in a 50-clone sample of a tetraploid crested wheatgrass breeding population. Significant (P < 0.05) differences were found among the clonal lines for dry matter (DM) yield, nitrogen (N), and N yield. Opportunities for genetic improvement, as indicated by the magnitude of the genetic variation for these characters, was significantly increased when the grasses were grown in association with alfalfa. Significant (P < 0.01) and positive correlations of clonal means between stand types indicated that differences among the clonal lines in DM yield, N content, and N yield were relatively consistent when grown with or without alfalfa. These results indicate that initial screening could be effectively done in tetraploid crested wheatgrass in the presence or absence of alfalfa. Final evaluation of breeding lines and experimental strains, however, should be done with alfalfa if the object is to develop cultivars to be grown in combination with that species.
    • Woody and herbaceous aboveground production of a Patagonian steppe

      Fernández-A., R. J.; Sala, O. E.; Golluscio, R. A. (Society for Range Management, 1991-09-01)
      Aboveground net primary production (ANPP) of the Patagonian steppe in southwestern Chubut (Argentina) was estimated using a harvest technique to assess the herbaceous (mainly grass) component and a double sampling technique to evaluate shrub production. The latter requires the measurement of plant dimensions and the harvest of shrub biomass in small plots. This technique, by virtue of having an explicit biological model which considers both shrub size and production per unit surface of plant, allows comparisons among years, sites, and treatments. Detailed estimates of ANPP yielded a value of 79 g of dry matter (DM) m-2 yr-1 (SE = 19 g DM m-2 yr-1) for an annual rainfall of 191 mm. Our estimates fits (+/- 17%) predictions of 4 models relating primary production to annual precipitation. Two thirds of production were accounted for by perennial grasses and one third by shrubs. A less detailed method, which uses only peak biomass, gave ANPP estimates for 4 additional years ranging from 21 to 75 g DM m-2 yr-1 while annual precipitation during this period ranged from 55 to 167 mm. There was a large reduction in ANPP during a year of extreme drought; however, there were no increases in ANPP during years with above-average precipitation. This suggests that the carrying capacity for the Patagonian steppe may not be linearly related to precipitation.
    • Grazing effects and range trend assessment on California bighorn sheep range

      Wikeem, B. M.; Pitt, M. D. (Society for Range Management, 1991-09-01)
      This study investigated the effect of grazing by California bighorn sheep (Ovis canadensis californiana) on plant community structure. Over 28 months from 1977 to 1979, bighorn diet consisted of 79 species, including 14 grasses, 47 forbs and bryophytes, plus 18 trees and shrubs. Grasses, forbs, and shrubs comprised 66.6, 18.9, and 14.5% of the diet, respectively. Three years of bighorn sheep grazing reduced (P < 0.05) leaf and culm lengths of bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith). Grazing generally reduced leaf length, basal diameter, culm (stem) length, and culm (stem) numbers of prairie Junegrass (Koeleria cristata Pers.), Sandberg's bluegrass (Poa sandbergii Vasey), needle-and-thread (Stipa comata Trin. & Rupr.), Thompson's paintbrush (Castilleja thompsonii Pennell), silky lupine (Lupinus sericeus Pursh), and snow buckwheat (Eriogonum niveum Dougl.). Vigor of arrowleaf balsamroot (Balsamorhiza sagittata (Pursh) Nutt.) was unaffected by grazing, despite its dietary importance. Total plant frequency remained unchanged between 1976 and 1983 in areas grazed by bighorn sheep, and in grazing exclosures. Total grass frequency declined from 46.5 to 30.8% within the exclosures, but increased from 44.7 to 48.8% in response to bighorn sheep grazing. Forb frequency remained unchanged after 7 years of bighorn sheep grazing while frequency of yarrow (Achillea millefolium L.) increased more inside exclosures than on the grazed area. Botanical composition of shrubs increased on grazed and ungrazed areas from 1976 to 1983, but frequency was unaffected by bighorn sheep grazing. Snow buckwheat and Wyeth buckwheat (Eriogonum heracleoides Nutt.) declined in response to bighorn sheep grazing. Successional trends caused by California bighorn sheep grazing differed from trends expected from cattle grazing.
    • Mefluidide effect on weeping lovegrass heading, forage yield, and quality

      White, L. M. (Society for Range Management, 1991-09-01)
      Weeping lovegrass [Eragrostis curvula (Schrad.) Nees.] provides high quality forage during May, but growth of floral stems causes a rapid decline in forage quality. The study objective was to determine which combination of date and rate of mefluidide [N-(2,4-dimethyl-5-[(trifluoro methyl) sulfonyl]amino]phenyl)acetamide], a growth regulator, would effectively decrease number of floral stems and thus maintain higher forage quality. Mefluidide (0.00, 0.28, 0.56, and 0.84 kg/ha) was applied to lovegrass on 1 of 3, 2, 5, and 5 dates in 1984, 1985, 1986, and 1987, respectively. Lovegrass was grown on a Pratt fine sandy loam (Thermic Psammentic Haplustalf) soil near Woodward, Okla. Factorial combinations of treatments were rerandomized within the study area each year. Plots (1.8 by 5 m) were replicated 6 times in a randomized complete block design. Forage was harvested in mid June to early July with a sickle bar at seed ripe. Mefluidide reduced the number of floral stems only when applied 1 week after floral primordium initiation. Mefluidide application 1 week earlier or later had little effect on number of floral stems, forage yield, in vitro dry matter digestibility (IVDMD), or crude protein (CP). Application of 0.56 kg/ba of mefluidide 1 week after floral primordium initiation decreased number of floral stems 58 to 93%, decreased forage yield 14 to 23%, increased percent leaves 4 to 32 percentage units, and had little effect on leaf yield. It increased whole-plant IVDMD 1.6 to 2.8 and CP 0.2 to 1.6 percentage units depending upon year. Generally, mefluidide had tittle effect on leaf or stem IVDMD or CP that averaged 49 and 7.5% for leaves and 39 and 5.1% for stems, respectively. The effective 'window' for mefluidide application is probably too short for practical use by farmers or ranchers.
    • Preference of wintering sage grouse for big sagebrush

      Welch, B. L.; Wagstaff, F. J.; Roberson, J. A. (Society for Range Management, 1991-09-01)
      A study determined sage grouse (Centrocercus urophasianus) preference for 3 subspecies and 9 accessions of big sagebrush (Artemisia tridentata Nutt.). The subspecies were mountain big sagebrush (A.t. ssp. vaseyana Rydb. Beetle), Wyoming big sage-brush (A.t. ssp. wyomingensis Beetle and Young), and basin big sagebrush (A.t. ssp. tridentata Nutt.). Accessions were collected at various sites in Utah and established in a uniform garden. Eleven plants for each accession or 33 plants for each subspecies were planted at random on a 2.13-m grid for a total of 99 plants. An enclosure with a top was constructed. Six birds were captured and placed in the garden. Preference was measured by the number of bites taken during the study and by estimates of percentage of leaves eaten at the end of the study. Results, by order of preference, were mountain big sagebrush, Wyoming big sagebrush, and basin big sagebrush. Within the most preferred subspecies there was distinct preference among accessions as measured by bite counts. When the forage of preferred subspecies or accessions was exhausted, the birds readily ate other subspecies or accessions.
    • Chemical composition of forage and feces as affected by microwave oven drying

      Karn, J. F. (Society for Range Management, 1991-09-01)
      Freeze drying, conventional oven drying, and microwave oven drying were compared with respect to their effect on the chemical composition of native range forage and feces from cattle grazing the forage. Forage was collected by hand harvesting and by esophageal-fistulated steers (extrusa) on 10 collection dates from 11 June to 15 Oct. in 1987 and on 6 collection dates from 2 June to 15 Sept. in 1989. Composite fecal samples were obtained from cattle grazing the same pastures the day following forage collections. Drying method had minimal effect on in vitro digestible organic matter (IVDOM), ash, neutral detergent fiber (NDF), nitrogen, and ash insoluble in neutral detergent (AIND) in hand clipped native forage. However, both microwave and conventional oven drying of extrusa resulted in greater NDF than freeze drying. Unexpectedly, IVDOM in microwave oven dried extrusa was equal to or greater than values for freeze dried material. There were no interactions between drying method and sampling date for any components measured in the extrusa. Microwave and conventional oven drying of feces resulted in greater NDF values than freeze drying, with microwave drying resulting in significantly greater NDF than conventional oven drying. There was also more AIND in heat dried feces, but nitrogen and ash levels were not affected by drying method. The data indicate that if nitrogen or ash are to be determined in hand cupped forage, extrusa, or feces, then microwave or conventional oven drying is acceptable; but if fiber levels are to be determined in these materials, then it appears they should be freeze dried for the most accurate results.
    • Control of woody plants in grazing lands on the Pacific Coast of Mexico

      Garcia-Holquin, M.; Bovey, R. W.; Schuster, J. L. (Society for Range Management, 1991-09-01)
      Greenhouse and field experiments were conducted to evaluate herbicides for control of Palma de llano (Sabal rosei Mart.), jarretaders (Acacia hindsii Benth), huinol (Acacia cymbispina Sprague & Riley), and guazima (Guazuma ulmifolia Lam.), woody species encroaching in grazing lands on the Pacific Coast of Mexico. In the greenhouse, picloram at 0.14 and 0.28 kg ae/ha killed all jarretadera, huinol, and guazima plants. Mixtures of picloram + clopyralid, dicamba, or triclopyr at 0.07 + 0.07 and 0.14 + 0.14 kg/ha also killed most plants. Trielopyr killed all huinol at 0.14 and 0.28 kg/ha but not all jarretadera or guazima. Clopyralid was effective on jarretadera and huinol but not as effective as picloram. Dicamba was ineffective on jurretadera and killed 88 to 100% of the huinol and gunzima plants at 0.28 kg/ha. The palm could not be grown in the greenhouse. In the field, foliar sprays of triclopyr or picloram st 0.4 and 0.3 g ae/L water, respectively, killed 70% or more of the jarretadera, huinol and gunzima but 77% or less of the palm. No herbicide successfully controlled jarretadera in 1988. Hexazinone applied to the soil killed 82% or more of the palm plants at 0.5 g ai/2.5 cm of stem diameter. Soil-applied tebuthiuron pellets were not effective on jarretaders or palm, but the briquettes (Brush Bullets) at 2 and 4 g/ 2.5 cm of stem diameter killed 50, 60, and 83% or more of the huinol, palm, and guazima plants, respectively.
    • Mountain mahogany and cottonseed meal as supplements for grass hay

      Nunez-Hernandez, G.; Wallace, J. D.; Holechek, J. L.; Galyean, M. L.; King, D. W.; Kattnig, R. M. (Society for Range Management, 1991-09-01)
      Sixteen wether lambs (avg weight 34.5 kg) were used to study the influence of 2 sources of supplemental protein, leaves of mountain mahogany (Cercocarpus montanus Raf.) and cottonseed meal, on N digestibility and balance, forage digestibility, and voluntary intake by sheep fed a low-quality grass hay. Treatments were grass hay alone (C), C plus cottonseed meal, C plus mountain mahogany, and C plus mountain mahogany and cottonseed meal. All supplements provided 42 g of supplemental crude protein per head daily. Treatments were assigned to wethers within blocks according to a randomized complete block design. Supplemental N increased (P < 0.01) N digestibility and balance regardless of source; however, lambs supplemented with mountain mahogany digested less (P < 0.01) N, but their N balance did not differ (P > 0.10) from those supplemented with cottonseed meal. Wethers supplemented with mountain mahogany plus cottonseed meal ate more (P < 0.05) organic matter (OM) than the average consumed by those given either of the 2 supplements alone. Protein supplementation did not affect (P > 0.05) OM or fiber digestibility. Range management practices that encourage dormant season utilization of mountain mahogany by ruminants in the Southwest could reduce supplemental protein needs; such practices might include reserving mountain mahogany sites for winter use as well as greater use of mountain mahogany (and other palatable, highly nutritive shrubs) in range restoration programs in mountainous areas.
    • Overgrazing: Present or absent?

      Wilson, A. D.; MacLeod, N. D. (Society for Range Management, 1991-09-01)
      This paper discusses the criteria needed for quantitative evidence of overgrazing and outlines some of the main pasture and external factors that promote overgrazing by herbivores. Overgrazing is defined as occurring where there is a concomitant vegetation change and loss of animal productivity arising from the grazing of land by herbivores. Confirmation of the loss of productivity requires the measurement of departures from the linear relationship between animal productivity and stocking rate for any given animal-pasture system. In the ex-ante situation of an experiment, overgrazing will be observed as a loss of linearity with time. in the ex-poste situation of a comparison between 2 paddocks of the some range type, but different grazing history, overgrazing will be observed as a difference in the optimum stocking rate. The outcome of a species change in terms of productivity is shown to be complex because of the interaction of the quality and quantity influences in both pasture and product. Influences that promote lower stocking rates include low cost-price margins and a negative relationship between product quality and grazing intensity. Conversely, higher stocking rates are promoted by the use of mineral supplements and products such as wool that have a positive relationship between product quality and stocking rate.
    • Interference between yellow starthistle and pubescent wheat-grass during grass establishment

      Prather, T. S.; Callihan, R. H. (Society for Range Management, 1991-09-01)
      Yellow starthistle (Centaurea solstitialis L.) and pubescent wheatgrass (Thinopyrum intermedium spp. barbulatum (Schur) Barkw. & D.R. Dewey) were seeded and subsequently thinned to 0, 130, 260, and 390 plants/m2 in a factorial arrangement. Aggressivity coefficients indicated that intraspecific interference became stronger than interspecific interference, based on biomass of either pubescent wheatgrass and yellow starthistle, as the density of both species increased in a 1:1 ratio. Pubescent wheatgrass provided 0.5 to 1.3 times as much intraspecific interference, plant for plant, as the interspecific interference caused by yellow starthistle. Yellow starthistle provided from 1.5 to 4.6 times as much intraspecific interference, plant for plant, as the interspecific interference caused by pubescent wheatgrass. Weekly leaf counts showed that intra- and interspecific interference from yellow starthistle was detectable 6 weeks after emergence. Weekly leaf counts showed that intraspecific interference from pubescent wheatgrass was detectable 7 weeks after emergence; interspecific interference from pubescent wheatgrass was not detectable using leaf count comparisons. Soil moisture at a 10 cm depth was correlated to leaf number of pubescent wheatgrass but not with leaf number of yellow starthistle. This may reflect the greater competitive ability of yellow starthistle.
    • Importance of hypocotyl hairs in germination of Artemisia seeds

      Young, J. A.; Martens, E. (Society for Range Management, 1991-09-01)
      The nature and function of hairs that occur on the lower portion of the hypocotyl of juvenile Artemisia seedlings was investigated. Our purpose was to determine if these hairs served an important function in seedling establishment of these species, which are often difficult to establish by direct seeding. The hypocotyl hairs occurred in a number of Artemisia species. The hairs form a dense ring around the bottom of the hypocotyl and the radicle emerges through the ring. Apparently, the function of the hairs is to attach the juvenile seedling to the surface of the germination substrate, which may aid in the penetration of the radicle into the substrate. Scanning electron microscope images of the hypocotyl hairs revealed the occurrence of mucilage which may aid in attaching the hairs to the substrate. In most studies, the seedling and breaking the contact of the hypocotyl hairs to the substrate reduced seedling survival and increased the number of surviving seedlings with abnormal geotropism.
    • Forest Service and livestock permitee behavior in relation to wildness designation

      McClaran, M. P. (Society for Range Management, 1991-09-01)
      Even though the Wilderness Act of 1964 provided for continuation of livestock grazing after wilderness designation, there has been continued debate about the Forest Service's implementation of this provision and the impact on livestock grazing permittees. The effect of wilderness designation, during the first 20 years after designation, on Forest Service and permittee behavior on Coronado and Tonto National Forests in Arizona was evaluated by (1) comparing changes in permitted AUMs, changes in permit ownership, and proportion of nonuse of permitted AUMs between paired wilderness and nonwilderness grazing allotments, and (2) assessing the importance of the proportion of an allotment in wilderness on these same behavioral parameters. In general, permitted AUMs increased on wilderness allotments but remained the same for nonwilderness allotments. However, there was no difference on Coronado National Forest when forests were analyzed separately. Compared to nonwilderness allotments, wilderness allotments had greater permittee turnover on Coronado National Forest, but there were no differences between wilderness and nonwilderness allotments when forests were combined. The higher the proportion of an allotment in wilderness, the faster the turnover of permit owners, but wilderness proportion did not affect nonuse or changes in permitted AUMs.
    • Range condition assessment and the concept of thresholds: A viewpoint

      Friedel, M. H. (Society for Range Management, 1991-09-01)
      Dissatisfaction persists with current approaches to range condition and trend assessment. Sometimes assessed condition does not truly represent the past or the potential of range. One of the likely causes is a failure to re-examine and change if necessary the theoretical basis of assessment, in line with developing understanding of ecological processes. The concept of thresholds of environmental change appears to provide a reasonable alternative in some circumstances to the concepts of gradual retrogression and secondary succession which are currently accepted. I suggest that environmental change can be discontinuous, with thresholds between alternative states. Once it threshold is crossed to a more degraded state, the former state cannot be attained without significant management effort, such as prescribed burning, ploughing, or herbicide application, rather than simple grazing control. Examination of data from extensive monitoring programs and from a study of grazing impact, as well as more general sources of information, indicates that thresholds of change may be identifiable in arid rangelands. A practical means of monitoring proximity to thresholds is available and, with the aid of multivariate analysis, the effects of spatial variability and season can be separated from those of management. The potential of this approach deserves investigation in a wider variety of environments.
    • Technical Note: Mineral content of guajillo regrowth following roller chopping

      Fulbright, T. E.; Reynolds, J. P.; Beasom, S. L.; Demarais, S. (Society for Range Management, 1991-09-01)
      Guajillo (Acacia berlandieri Benth.) is browsed by white-tailed deer (Odocoileus virginianus Raf.). We determined phosphorus (P), potassium, (K), calcium (Ca), and magnesium (Mg) of browse from roller-chopped (July 1986 and July 1987) and nontreated guajillo. Browse from regrowth was temporarily higher in P than browse from nontreated plants. Potassium was higher in leaves from plants roller chopped in 1987. Calcium and Mg tended to be lower in leaves from roller-chopped plants. Roller chopping temporarily increases P and K, but whether or not browse from roller-chopped guajillo meets P and K requirements for deer is unknown.
    • Utilization patterns by Angora goats within the plant canopies of two Acacia shrubs

      Owens, M. K. (Society for Range Management, 1991-09-01)
      Uneven distribution of livestock in large pastures results in some areas receiving more use than the average and some areas receiving little or no use. Six 2-ha experimental pastures on a shallow ridge site were stocked with 2, 4, or 6 Angora goats per ha to reflect different levels of use found in large pastures of south Texas. Two additional pastures on a sandy loam site were stocked with 2 goats per ha. Utilization estimates were made in each pasture using a twig diameter-weight relationship. Estimates of utilization of guajillo (Acacia berlandieri) and blackbrush (A. rigidula) were made in canopy strata which the goats could reach in a quadrupedal stance (low), a bipedal stance (middle), and from the zone above the bipedal stance (high). These measurements were repeated 3 times during the grazing season. Nonlinear regressions of diameter on weight (Y = aXb) collected from plants in control pastures provided a better fit than log-log regressions in almost every instance. Fit index values, which are analogous to R2 values for linear equations, ranged from 0.82 to 0.94 for nonlinear equations and from 0.62 to 0.88 for the log-log regressions. Goats exhibited different grazing strategies by using the canopy strata differently for the 2 plant species. Percent utilization in the middle strata was higher than in either of the other 2 canopy strata within each grazing treatment and for each plant species. Cumulative use in the middle strata for guajillo was 79% compared to 63% in the low and 28% in the high strata. Blackbrush also had highest use in the middle strata with 39% use compared to 27 and 9% for the low and high canopies, respectively. By the third sampling period, use of guajillo in the 2 lowest canopy strata declined and use of blackbrush increased over the first 2 sampling periods. Average grazed twig diameter within each grazing treatment did not vary significantly in the low strata throughout the growing season. On heavily used sites, averaged grazed twig diameter increased in the 2 highest canopy layers as the season progressed. The size of grazed twigs in the middle zone on the heaviest grazed sites was significantly higher than in any other canopy strata.