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Vegetation canopy cover on upland and lowland sites inside and outside a ZZyear-old exciosure in big sagebrush (At-tern& tridentutu trident&z) range was evaluated by sampling for canopy cover. The area outside the exciosure had received moderate use of grazabie forage by cattle in the late winter and spring for the past 22 years. The two sites did not show a consistent response to grazing. Big sagebrush canopy cover was higher inside the exciosure on the upland site and higher outside the exciosure on the lowland site. Big sagebrush dominated the canopy cover both inside and outside the exciosure on both sites and relatively little understory was present. Forbs were nearly absent from the area, which is atfributed to a past history of heavy sheep grazing. Elimination of grazing had little effect on vegetation composition on both sites studied. Because of its size (approximately 50 million hectares) the big sagebrush (Artemisia tridentata) range type is of considerable importance in the western United States. Major provinces within the big sagebrush range type include the following: Columbia River (Hironaka 1979); the Great Basin (West 1979); the high plains of Montana, Wyoming and the Dakotas (Johnson 1979); and the Colorado plateau (West 1979). The Colorado plateau province of southwestern Colorado and northwestern New Mexico has had the longest history of livestock grazing, which dates back to the seventeenth century (Carlson 1969). Because of both widespread and heavy grazing in the nineteenth and early twentieth centuries by first sheep and later cattle (Wooten 1908), little is known about the original vegetation. Our review of the literature shows the Colorado Plateau has received the least study of the four big sagebrush provinces. Information concerning successional changes that result from reduction or removal of livestock grazing pressure is not available for this province. Exclosures can be a useful tool to the range manager for evaluating and interpreting both short-term and long-term grazing influences of domestic and wild animals (Daubenmire 1968). Moderate to light grazing appears to be beneficial to most range plant communities (Holechek 1980) although further study is needed. Changes in vegetation that result from grazing management are difficult to separate from those that result from changes in climate unless ungrazed areas are available for comparison with grazed areas within the same pasture. The objective of this study was to compare the vegetation canopy cover of different moderately grazed basin big sagebrush (Artemisia tridentata tridentata) sites in northcentral New Mexico with that of the same sites when they had received 22 years of protection. Authors are associate professor of range ecology and graduate research assistant. Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003. This report is article 900. Agricultural Experiment Station, New Mexico State University, Las Cruces 88003. Manuscript received October 10, 1981. JOURNAL OF RANGE MANAGEMENT 36(4), July 1963 Methods The study area was located 40 km northwest of Taos, N. Mex., in a 25-35 cm precipitation zone at 1800-2,000-m elevation. Most (65%) of precipitation occurs in the spring and summer; July and August are months of peak rainfall. Soils of the area belong to the order aridisol and the suborder argid due to their high clay content. Soil texture ranges from a clay loam on lowland sites to a silty clay loam on upland sites. Soil depth averages about 170 cm on lowland sites and 140 cm on upland sites. Vegetation is heavily dominated by big sagebrush (Artemisia tridentata tridentata) with an understory of primarily blue grama (Bouteloua gracilis) on the upland sites and western wheatgrass (Agropyron smithii) on the lowland sites. Other species found on the study area included fourwing saltbush (Atriplex canescens), galleta (Hilaria jamesii), common winterfat (Ceratoides lanata), cactus (Opuntia sp.), scarlet globemallow (Sphaeralcea coccinea), Russian thistle (Salsola kali), broom snakeweed (Xanthocephalum sarothrae), summer cypress (Kochia seoparia), ring muhiy (Muhlenbergia torreyi), and crested wheatgrass (Agropyron cristaturn) (Stephenson 1982). Forbs are almost entirely absent with the exception of well-traveled roadsides. The pasture selected for study is controlled by the Bureau of Land Management. We believe it is typical of big sagebrush ranges in northern New Mexico in terms of precipitation, soils, vegetation, grazing history, and grazing management. It is characterized by relatively flat roiling terrain (uplands) with slight depressions (lowlands) caused by waterdrainage. Uplands compriseabout 80% of the area with lowlands comprising about 20%. During the past 25 years the study pasture had been grazed by cattle at a moderate stocking rate (30 to 50% use of current years growth) during the late winter and spring until early June. in 1958 an exclosure of approximately 16 ha was built with woven wire to prevent use by both livestock and game animals. It was located in a “key area”as discussed by Stoddart et al. (1975). The western half of the exclosure was on a lowland site and the eastern half was on a upland site. A modification of the line-intercept procedure of Canfield (1941) was used tosamplevegetationcanopycoverin August 1981. For sampling canopy cover, a stick of Im in length incremented in millimeters was used instead of an extended line. Eight transects were randomly selected based on consecutive numbering of fence posts at the west and east ends of each exclosure. Ten-meter buffer areas immediately inside and outside the ends of each exclosure were omitted from sampling to avoid influences of the fence. Each transect involved IO subunits of 5m in length. Cover was sampled for all 10 subunits of each transect by perpendicular orientation of the meter stick to the left side at the end of each subunit. Two observers independently sampled each location. The number of jackrabbit pellets intercepting the meter stick was recorded for all subunits. A one-way completely randomized design with observers as subsamples was used to evaluate experimental results (Steel and Torrie 1960).

Comparison of Big Sagebrush Vegetation in Northcentral New Mexico under Moderately Grazed and Grazing Excluded Conditions