Vegetation changes after livestock grazing exclusion and shrub control in the southern Chihuahuan Desert

Vegetation cover and production were evaluated after nearly 7 years of livestock grazing exclusion and shrub control in an area with a long history of heavy livestock grazing in the southern Chihuahuan Desert, Mexico. An exclosure was established to prevent livestock grazing. In half of the excluded area, the main shrub, Larrea tridentata , was mechanically controlled. Outside the exclosure, heavy livestock grazing occurred as customary and shrubs were not controlled. Absence of grazing resulted in 50% higher grass cover and 35% higher total biomass. Larrea tridentata cover was twice as high on the grazed area as on the ungrazed area. Vegetation cover was dominated by grasses (42%) in the ungrazed area, whereas in the grazed area, cover was equally divided between grasses (28%) and shrubs (27%). Shrub control did not affect vegetation cover or herbage production. Multivariate analysis confirmed that inside the excluded area, shrub control had little impact on the plant community. The effect of grazing, however, clearly distinguished the community outside the exclosure from that inside the exclosure.     

Response of winterfat ( Ceratoides lanata ) communities to release from grazing pressure

Sixteen study sites were established in grazed and ungrazed stands of winterfat in Kane County, Utah. The area is located within the winter range of cattle and along U.S. Highway 89 between Kanab, Utah, and Page, Arizona. Road construction in 1957 dissected several winterfat communities, and following fencing part of the communities were released from grazing. Differences in species composition, vegetation, and soil characteristics between grazed and ungrazed sites were assessed. Major differences in site characteristics appeared due to the influence of winter grazing by cattle. Winterfat and Indian ricegrass showed increased cover on the nongrazed sites following release from grazing pressure. Winterfat also showed significant negative interspecific association patterns with all major species.     

Grasshopper densities on grazed and ungrazed rangeland under drought conditions in southern Idaho

Low-density grasshopper populations were sampled at 15 pairs of rangeland sites in south central Idaho. One site of each pair had not been grazed by livestock for at least 10 years. Grazed sites were managed under normal grazing regimes established by the Bureau of Land Management. Mean grasshopper density was higher on ungrazed sites than on grazed sites. Proportions of Melanoplus sanguinipes were higher on ungrazed sites than on grazed sites and were higher on annual grasslands than on other vegetation types. Effects of grazing appeared to be independent of vegetation type. Proportions of Comhpocerinae, a subfamily of grasshoppers that feeds almost exclusively on grasses, were affected by vegetation type, but not grazing. Crested wheatgrass seedings supported the highest proportions of Gomphocerinae. Proportions of Oedipodinae were affected by grazing and vegetation type. Higher proportions of Oedipodinae were found on grazed sites than on ungrazed sites, and on sagebrush/grass sites than on annual grasslands. Results indicate that livestock grazing during drought conditions tends to reduce grasshopper populations in southern Idaho rangeland.     

The effect of livestock grazing on the rainbow grasshopper: population differences and ecological correlates

This study examined the effect of livestock grazing on a common herbivore in semiarid grasslands of the Southwest: the rainbow grasshopper, Dactylotum variegatum . Population attributes and key environmental variables were compared between sites on active cattle ranches and sites on a 3160-ha ungrazed sanctuary. Although density of D. variegatum nymphs did not differ significantly between grazed and ungrazed sites, adult density was significantly lower on grazed sites, and sex ratios differed between grazed and ungrazed sites over time. Grazed sites had higher percentages of bare ground and fewer Baccharis pteronioides , a common shrub. However, only bare ground was highly correlated with adult D. variegatum density; lower adult densities were associated with more bare ground. At a smaller scale, D. variegatum tended to be more abundant in areas with B. pteronioides on grazed sites and less abundant in areas on ungrazed sites. This study suggests that cattle grazing influences ecological variables important in determining density, sex ratio, and spatial distribution of D. variegatum at both large and small spatial scales.     

Cryptogams, vascular plants, and soil hydrological relations: some preliminary results from the semiarid woodlands of eastern Australia

Grazed and ungrazed sites were examined in a semiarid woodland in eastern Australia to determine relationships within various types of cryptogams, and the role of cryptogams in pasture dynamics, infiltration, and water erosion. Strong relationships were found between vascular plant cover and cover of cryptogams for nine rangeland sites over an 18-month period. In the absence of vascular plants, sites with low cover of cryptogams were dominated by algae. The presence of a cryptogamic crust had no significant effect on infiltration at ungrazed sites but significantly increased infiltration at some grazed sites. Splash erosion was very low on soils with at least 50% cryptogam cover. Below this level splash erosion increased markedly, along with the proportion of fine sediments lost.     

Cryptogamic soil crusts: recovery from grazing near Camp Floyd State Park, Utah, USA

The effects of grazing on the cryptogamic and vascular plant communities at two sites near Camp Floyd State Park, Utah County, Utah, were studied. The grazed site was subject to heavy grazing up until seven years prior to the study. The ungrazed site within the park boundaries had been protected from grazing for 20 years prior to the study and had a well-developed algal-lichen-moss crust. We found that the algae of the grazed site had recovered in terms of degree of crusting. There were no significant differences in the algal communities of the two sites when prevalent species were used as blocks in the ANOVAR analysis. However, when major algal groups were used as blocks, the analysis was significant, with the more recently grazed site having lower algal frequency. This difference, together with a few compositional differences, indicates that, although the algal community seven years following grazing is very similar to the algal community free of grazing for 20 years, the seven-year site is still in the process of recovery and community development. The diatom collections had a higher density in the grazed site, though the difference was not significant. Recovery of the lichen and moss community was not complete. The lichen Collema tenax and the mosses Bryum pallescens and Tortula ruralis were all significantly more abundant in the ungrazed area. Total cover of the lichen and moss components of the soil crusts was significantly lower in the more recently grazed area. Vascular cover was also lower.     

Response of reptile populations to different land management practices on the Idaho National Engineering Laboratory Site

Populations of reptiles were examined in grazed and ungrazed habitats dominated by sagebrush ( Artemisia tridentata ) or by crested wheatgrass ( Agropyron cirstatum ) on the Idaho National Engineering Laboratory (INEL) Site in southeastern Idaho. The sagebrush lizard ( Sceloporus graciosus ) and the short-horned lizard ( Phrynosoma douglassi ) were the only species of reptiles encountered in sufficient numbers to permit statistical analysis. Both of these species preferred sagebrush habitats to areas dominated by crested wheatgrass. The sagebrush lizard was most abundant in the native, ungrazed, sagebrush habitat, and the short-horned lizard was most plentiful in the sheep-grazed area dominated by big sagebrush.     

Effects of long-term livestock grazing and habitat on understory vegetation

The herbaceous understory stratum contains most of the plant diversity in ponderosa pine ( Pinus ponderosa P. & C. Lawson var. scopulorum Engelm.) forests of the American Southwest and provides critical food and habitat for many wildlife species. During the last century, this stratum has been affected by livestock grazing and by increased dominance of overstory trees. We sampled a unique grazing exclosure to examine the relative importance of long-term livestock grazing (grazed or ungrazed) and habitat (park or tree) on the understory community. We sampled 3 plots of 192 contiguous quadrats (each quadrat 0.5 m 2 ) in each of the 4 treatment combinations, for a total of 2304 quadrats. Species-area curves were generated by aggregating quadrats into nonoverlapping areas at grain sizes of 0.5 to 576 m 2 . The effects of habitat and grazing on species density were evident at very different scales. Species density was higher in park than tree plots at scales ≤32 m 2 but did not differ between habitats at larger scales. Species density differed minimally between grazed and ungrazed treatments at small grains, but grazed plots contained more species than ungrazed plots at larger grains. Grazing treatments differed at smaller grains (to 4–8 m 2 ) than did habitats (to 32 m 2 ), with respect to density of native species and graminoids. Grazed plots had more exotic species than ungrazed plots at all grain sizes, though few exotics were present. Twenty-two species were identified as indicator species associated with habitats and/or grazing treatments. Evaluations of plant community response to treatments would be improved by accounting for the grain at which data have been collected and analyzed and by identifying indicator species associated with various treatments. These data would enable more-informed conservation and management decisions.     

Examining ecological consequences of feral horse grazing using exclosures

Although feral horses have inhabited western North America since the end of the 16th century, relatively little synecological research has been conducted to quantitatively characterize how they interact with ecosystem components. Because feral horses exhibit watering behavior markedly different from that of domestic cattle, it is particularly important to evaluate response of ecosystem elements near water sources to horse use. To assess this response, we performed live-trapping of small mammals and 2-tiered vegetative sampling in 2 mountain ranges in central Nevada in the interior Great Basin, USA. At low elevations, plots around horse-excluded springs exhibited notably greater plant species richness, percent cover, and abundance of grasses and shrubs, as well as more small mammal burrow entrances than plots at horse-grazed springs. At high elevations, meadows protected from grazing exhibited maximum vegetation heights 2.8 times greater than vegetation grazed by horses only and 4.5 times greater than vegetation grazed by horses and cattle. Species richness in quadrats was most different between the horse-and-cattle-grazed meadow and its ungrazed counterpart, suggesting the possibility of synergistic effects of horse and cattle grazing in the same location. This study, the first in the Great Basin to investigate quantitatively ecosystem consequences of feral horse use with exclosures, represents a preliminary step in identifying factors that determine the magnitude of horse grazing impacts.     

Effects of livestock grazing exlosure on aquatic macroinvertebrates in a montane stream, New Mexico

Aquatic macroinvertebrate populations inhabiting reaches of a stream within areas excluded from livestock grazing for a decade were markedly different from those in grazed areas when density, biomass, biotic condition indices, and mean chi square indices of the two populations were compared. Increased densities and biomasses of more tolerant forms of macroinvertebrates were observed in grazed reaches. Because pretreatment data were not available, differences in macroinvertebrate populations and relative tolerances of taxa in grazed and ungrazed areas could be as easily attributed to linear changes in stream habitat as to removal of domestic livestock. Results of this study have implications for the design of future research on the effects of livestock grazing on stream environments and biota: (1) baseline/pretreatment information is prerequisite, and (2) the study should take a watershed (ecosystem) approach.     

Grazing and passerine breeding birds in a Great Basin low-shrub desert

Densities of passerine breeding birds were compared between four range pastures variously grazed by sheep over a 50-year period. The experimental pastures, located at the Desert Experimental Range in southwestern Utah, included three grazed and one ungrazed. Grazed pastures were each heavily stocked and grazed annually at one of three winter seasons (early, middle, or late). Important structural (physiognomic) and compositional differences existed in the vegetation of the experimental pastures. Horned Larks ( Eremophila alpestris [Linnaeus]), numerically dominant in the pastures, apparently responded to those differences. Black-throated Sparrows ( Amphispiza bilineata [Cassin]) and Loggerhead Shrikes ( Lanius ludovicianus Linnaeus) were less common and found as breeding birds only in dry wash habitats. No significant differences were found between the pastures in estimates of total breeding bird populations, bird standing crop biomass, or bird species richness.     

Effects of cattle grazing on North American arid ecosystems: a quantitative review

A quantitative review was conducted of the effects of cattle grazing in arid systems on 16 response variables ranging from soil bulk density to total vegetative cover to rodent species diversity. Various studies from North American arid environments that used similar measures for assessing grazing effects on the same response variables were used for the review; each study was assigned to serve as a single data point in paired comparisons of grazed versus ungrazed sites. All analyses tested the 1-tailed null hypothesis that grazing has no effect on the measured variable. Eleven of 16 analyses (69%) revealed significant detrimental effects of cattle grazing, suggesting that cattle can have a negative impact on North American xeric ecosystems. Soil-related variables were most negatively impacted by grazing (3 of 4 categories tested were significantly impacted), followed by litter cover and biomass (2 of 2 categories tested), and rodent diversity and richness (2 of 2 categories tested). Vegetative variables showed more variability in terms of quantifiable grazing effects, with 4 of 8 categories testing significantly. Overall, these findings could shed light on which suites of variables may be effectively used by land managers to measure ecosystem integrity and rangeland health in grazed systems.     

Roadside foraging by kangaroo rats in a grazed short-grass prairie landscape

We used live-trapping and foraging experiments to describe use of roadside vegetation by kangaroo rats ( Dipodomys ordii ) in short-grass prairie in Colorado, and to determine whether this species' perception of predation risk differed between roadside habitats, where predators were expected to be most active, and locations 120 m into adjacent grazed pastures. Giving-up densities (GUDs) were measured in paired seed trays placed beneath saltbush ( Atriplex canescens ) shrubs and in the open, 3 m from shrubs along transects in roadside and pasture locations. Trials were conducted on nights with a partial (1st-quarter), full, and new moon to assess how intensity of risk affected microhabitat use. Kangaroo rats were much more abundant in areas with saltbush cover than in grazed prairie, and were 4–6 times more numerous along roadsides in saltbush areas than in other locations. On dark nights and in pasture locations, foraging rates of kangaroo rats were similar in shrub trays and open trays. The fewest seeds were removed (i.e., GUDs were highest), however, in open trays along roads on moonlit nights, suggesting that kangaroo rats recognized potential risks associated with roadsides on bright nights. The high numbers of kangaroo rats along roads suggest that benefits associated with these habitats (ease of digging, dust bathing, higher soil seed banks) exceed the costs associated with higher risk of mortality from predators and vehicles. Our results demonstrate how foraging decisions differ depending on the spatial and temporal contexts in which behaviors are measured, and underscore the potential value of less common habitats such as road margins for increasing landscape-scale diversity and wildlife habitat in grazed grasslands.     

Dry-year grazing and Nebraska sedge ( Carex nebraskensis )

In 1984 (a dry year), Tule Meadow, in the Sierra National Forest, California, was well grazed after several years of light use. This situation provided the opportunity to study responses of Nebraska sedge ( Carex nebraskensis ), an important forage species in mountain meadows, to protection and grazing. Rooted shoot frequencies and densities in fall 1984 and spring 1985 were the same within an exclosure and on the grazed area. Residual herbage (shoot weight) in fall and shoot heights in spring were greater within the exclosure. Lower spring shoot heights on the grazed area may relate to fall regrowth and reduced insulation induced by grazing. Nitrogen and potassium content of fall herbage was greater on the grazed area. Phosphorus content was the same both inside and outside the exclosure.     

Records of the yellow-nosed cotton rat ( Sigmodon ochrognathus ) in southwestern New Mexico

The yellow-nosed cotton rat ( Sigmodon ochrognathus ) previously was known only from extreme southwestern New Mexico in the Peloncillo and Animas mountains. Here I document S. ochrognathus at 3 localities from the Big Burro and Mogollon mountains in southwestern New Mexico. My northernmost capture represents an extra-limital record of 160 km north of prior records in southern New Mexico and represents the northernmost occurrence in North America. Lack of intensive mammalian surveys in the region render it difficult to interpret my recent captures, but the most parsimonious explanation is that captures likely represent overlooked populations. I captured S. ochrognathus in grassy areas ungrazed by domestic livestock along the Gila River. Understanding the use of limited grassland habitats along arid rivers by terrestrial vertebrates in the region is important because many of these grasslands have been converted to agricultural lands or are grazed by livestock.     

Grazing impacts on sagebrush communities of central Utah

Twenty-three study sites were established in the sagebrush communities bordering Utah Lake. Relic (ungrazed) and grazed stands were represented in the sample. Differences in species composition, vegetation, and soil characteristics were assessed. Major differences in species composition and vegetative characteristics were due to the influence of grazing. Major changes were loss of native perennial grass cover, and increases in cover from introduced annual species. Differences in the soil characteristics were due to habitat rather than grazing influences.     

C 3 and C 4 Species Changes Identified by δ 13 C values of soil organic matter in a Colorado prairie

We measured carbon isotope signatures (δ 13 C) from 0-10 cm and 10-20 cm soil depth intervals for grassland soils near Boulder, Colorado. These grasslands included tall-, short-, and mixed-grass prairies that were grazed, ungrazed, or hayed. Soils exhibited δ 13 C signatures consistent with observations that current sites are a mix of C 3 and C 4 species, with C 3 plants more abundant in mixed-grass than in native tall- or shortgrass prairies. The δ 13 C signatures were not significantly different for grassland types; however, management treatments (grazing, no grazing, haying) significantly influenced changes in soil δ 13 C signatures from the 0-10 cm to 10-20 cm soil depth intervals. We observed a correlation ( r = 0.63) between isotopic values of surface soils and percent native species in total vegetation cover. Overall, the community type with the lowest percentage of nonindigenous species cover had the most enriched δ 13 C signature. Sites currently grazed by prairie dogs, cattle, or both herbivores had stronger C 3 signatures, indicating that grazing may have increased C 3 plant productivity in these communities at the expense of C 4 grasses. This finding differs from studies of native shortgrass steppe where grazing has the opposite effect on the relative abundance of these 2 functional groups of plants. This result, along with the correlation between C 3 isotopic values and nonnative vegetation abundance, provides evidence that management practices that maintain dominance of C 4 grasses should be encouraged.     

Species richness and California voles in an annual and a perennial grassland

Populations of a common burrowing rodent, Microtus californicus (the California vole), thrive in ungrazed or lightly grazed grasslands in coastal California. Two sites ungrazed by livestock, one dominated by native perennial grasses and another dominated by invasive annuals, were evaluated over 2 consecutive years for the relationship between plant species richness and location of M. californicus burrow entrances (burrows). Plant species and burrows were sampled as present or absent in contiguous 1-m 2 quadrats on a 100-m 2 grid. Quadrats with burrows averaged significantly more plant species than quadrats without them (11.3 vs. 9.9 species, P < 0.001). Burrows found in 1996 were not correlated with species richness in 1995, suggesting that voles affect richness rather than seek it out. Vole burrow locations showed significant clumping on the annual site and trended toward clumping on the perennial site in both 1995 and 1996. Because voles seem to create a clumped pattern with their burrow entrances, the associated increase in plant species richness may have a strong effect on the overall structure of the plant community. A quantitative comparison of the 2 sites showed that the plant matrix of the perennial site contained flora of the annual site. This similarity in plant species composition may allow for similar treatment of our 2 types of sites and potentially other California grasslands. Undetected increases in vole populations with livestock grazing reduction may account for the erratic results from grasslands management research and the inconsistent success of derived management practices.     

Conservative and moderate grazing effects on Chihuahuan Desert wildlife sightings

Seasonal wildlife observations were made along transects on 2 pastures conservatively grazed (36% use of perennial grasses) and 2 pastures moderately grazed (47% use of perennial grasses) in south central New Mexico in non-drought (1997) and drought years (1998). Experimental pastures were similar in soils, terrain, spacing of watering points, and brush cover. Average ecological condition score for the conservatively grazed pastures was 60% compared with 64% for moderately grazed pastures. Throughout the study total standing vegetation understory herbage levels were higher ( P P > 0.05) between conservatively and moderately grazed pastures. Black-tailed jackrabbit ( Lepus californicus ) sightings were higher ( P Antilocapra americana ), scaled quail ( Callipepla squamata ), mourning doves ( Zenaida macroura ), and desert cottontails ( Sylvilagus auduboni ) showed no differences ( P > 0.05) between conservatively and moderately grazed pastures. Dry conditions in 1998 depressed total wildlife sightings by > 50% compared to 1997. Both songbird and gamebird (particularly mourning dove) sightings were severely reduced in the dry compared to wet year ( P < 0.05). Our results are consistent with Nelson et al. (1997) that livestock grazing at intermediate levels had no effect on most Chihuahuan Desert upland wildlife species, and that drought years severely depress wildlife sightings.