Ungrazed Sites Research Articles

Response of C3 and C4 grasses to supplemental summer precipitation

Rangeland plant productivity and species composition are affected by moisture availability and grazing intensity. We examined warm- and cool-season grass productivity and relative distribution on grazed and ungrazed sites, receiving either natural precipitation or precipitation plus limited supplemental irrigation. The amount of additional water varied depending on rainfall during the previous week and was intended to shorten the interval between precipitation events and provide a more uniform seasonal moisture distribution. Irrigation treatments were superimposed in 1997 and 1998 on paddocks that had not been grazed for about 55 years or continuously stocked during the growing season for 15 years. Cool-season grasses dominated the ungrazed plots, comprising about 90% of the total biomass. In the grazed plots, the proportion of C3 grasses ranged from 30 to 81%. The proportion of C3 grasses in the grazed treatment decreased from spring to fall and decreased with supplemental irrigation. Root biomass was greater and more concentrated near the soil surface in the grazed compared with the ungrazed plots. Irrigation had no effect on root biomass in the grazed plots while irrigation reduced total root biomass and root biomass in the top 5 cm of the soil profile in the ungrazed plots. Irrigation increased total aboveground biomass only at the August 1997 harvest. Aboveground biomass of warm-season grasses, however, increased under irrigation in the grazed plots in August and November 1997 and August 1998. These increases, however, were offset by a reduction in cool-season grasses in November 1997 and August 1998. Warm-season grasses were particularly responsive to the supplemental irrigation treatments and tended to increase under irrigation at the expense of cool-season grasses. Because of the increased proportion of warm-season grasses, grazed plots were more responsive to irrigation than ungrazed plots.

Species richness of annual legumes in relation to grazing in Mediterranean vegetation in northern Israel

Species richness of annual legumes in step-point transects was analyzed for 79 pairs of grazed and ungrazed sites of Mediterranean vegetation in northern Israel. Seventy-eight species of annual legumes belonging to 17 genera were sampled. Species richness of all annual legumes of Medicago and Trifolium was significantly greater, by 25-42%, on the grazed compared to the ungrazed site of site-pairs. Legume richness was significantly greater on Cretaceous and Eocene sedimentary rocks compared to younger Neogene and Pleistocene sediments, with intermediate richness on basalt. It was significantly lower in sites with 400-500 mm rainfall compared to 500-900 mm, and in wetland compared to grassland, shrubland, and woodland. Species richness of annual legumes, Medicago and Trifolium, increased significantly from zero or low grazing intensity to high intensity. A consistent, not significant reduction of species richness was observed at extremely high grazing intensity. Many species of small annual legumes increased in cover with grazing intensity. Erect or twining species did not show this response. The tendency of increased richness of annual legumes with grazing was confirmed for subhumid Mediterranean communities, but it may be reversed at extremely high grazing intensities, or in semiarid communities grazed by sheep, and for some legume taxa. Management for in situ conservation of the entire annual legume flora in productive Mediterranean vegetation requires, in different parts of the landscape, continuation of intense grazing and relative protection from grazing.

Effects of frequent fires and grazing on stable nitrogen isotope ratios of vegetation in northern Australia

AbstractThe ratios of stable nitrogen isotopes expressed as δ15N values can indicate the openness of nitrogen cycles in ecosystems. Southwards through the Northern Territory, values of foliar δ15N in savanna trees increase as mean annual rainfall decreases from approximately 1800 mm to approximately 750 mm, with foliar δ15N thereafter decreasing toward arid central Australia. Recent literature argues that this pattern is caused by higher grazing intensity in semi‐arid savannas, but counter views have attributed the pattern more directly to variations in aridity. In this paper, grazed and ungrazed sites in a semi‐arid savanna are compared, and it is shown that grazing has a relatively small effect on the positive foliar δ15N values of grasses, but no effect on δ15N values of trees. This gives little support to the argument that variations in grazing pressure at the scale of hundreds of kilometres could result in detectable differences in the foliar δ15N values of trees. I then compare the semi‐arid savannas with mesic savannas, where fires are frequent, and with mesic rainforests, which are rarely burnt. Greater foliar δ15N values in rainforest and fire‐excluded mesic savannas than in frequently burnt savannas suggests that fire regimes affect foliar δ15N. The previously observed pattern in δ15N values along the rainfall gradient in the Northern Territory is consistent with trends in fire frequency and possible direct effects of fire, but further work is required to determine the relative impacts of aridity and fire. Within a particular rainfall regime, foliar δ15N values may indicate historical fire frequencies.

Short-Term Effects of Cattle Exclusion on Riparian Vegetation in Southeastern Kansas

Abstract Effects of cattle exclusion on the structure and composition of riparian vegetation were observed in a 2-yr study in southeastern Kansas. The study was conducted within riparian habitats on the 5,263-ha Kansas Army Ammunition Plant in north-central Labette County, Kansas. Three grazed and three ungrazed riparian areas were sampled in 1996 and 1997 to monitor vegetation changes in response to livestock exclusion. Total understory, grass, and litter cover were significantly different between the grazed and ungrazed study sites with mean cover estimates being higher (16.3%, 14%, and 12.1% greater respectively) in the ungrazed sites. A significant difference in the percentage of bare ground was observed between the grazed (24.6%) and ungrazed (12.5%) study sites. No difference in herbaceous vegetation height was detected between study sites in 1996. In 1997, mean herbaceous vegetation height differed significantly from 1996 (study sites combined) and was greater (95.6 cm vs. 65.6 cm) in the ungrazed ...

Influence of Grazing by Bison and Cattle on Deer Mice in Burned Tallgrass Prairie

Abstract We studied the influence of grazing by bison (Bos bison) and by cattle (B. taurus) on deer mice (Peromyscus maniculatus) in tallgrass prairie at the Konza Prairie Biological Station in 1997 and 1998. Small mammals were sampled by one 10-station trapline in each of four bison-grazed enclosures, four cattle-grazed enclosures and four ungrazed sites. Enclosures were 4.9 ha and the biomass of grazers in each was similar. All sites were burned annually. We sampled small mammals for 4 consecutive nights in spring before fire, in spring after fire and in autumn. Deer mice were the most abundant species (n = 285; 83% of all small mammals) captured in all treatments and in each trapping period. Deer mice were significantly more abundant in bison-grazed and cattle-grazed sites than in ungrazed sites in spring before fire (P < 0.01 and P < 0.05, respectively), but were similar in abundance in grazed and ungrazed sites following fire. Abundance of deer mice was significantly higher in bison-grazed sites than...

The Impact of Sheep Grazing on Net Nitrogen Mineralization Rate in Two Temperate Salt Marshes

Abstract: Nitrogen mineralization rate was studied in grazing trials with three different stocking rates (0, 3, 10 sheep ha‐1) in two man‐made salt marshes, viz. a Puccinellia maritima‐dominated low salt marsh and a high salt marsh dominated by Festuca rubra. Mineralization rates were derived from the amounts of mineral N which accumulated in situ during six‐week incubation periods in tubes containing undisturbed soil cores from the upper 10 cm soil layer. The annual rates of net N mineralization were significantly higher in the better drained, high salt marsh (71 ‐ 81 kg ha‐1 yr‐1) than in the low salt marsh (39 ‐ 49 kg ha‐1 yr‐1). High amounts of belowground litter accumulated in the low salt marsh due to frequent water logging. Both N mineralization and nitrification rate were negatively correlated with soil water content. In the Puccinellia maritima salt marsh, grazing had neither an effect on N mineralization rates during any of the incubation periods nor on annual mineralization rates. In the Festuca rubra salt marsh, N mineralization rates increased earlier during spring at the intensively grazed site than at the moderately grazed and the ungrazed site. N mineralization and nitrification rates were significantly higher at the ungrazed site than at the intensively grazed site during the period of peak net N mineralization from the end of April until mid‐June. Although sheep grazing affected the seasonal pattern of N mineralization in the high marsh, grazing did not affect the annual rate of net N mineralization.

Effects of Grazing on the Demography and Growth of the Texas Tortoise

Abstract: Considerable effort has been exerted in attempts to understand the complex ecological effects of grazing. North American tortoises, by virtue of their distribution, provide a good model taxon through which to study how grazing effects vary with grazing regime, habitat, and climate. We studied the Texas tortoise ( Gopherus berlandieri ), which is restricted primarily to privately owned rangelands of southern Texas and northeastern Mexico. Management of this species is hampered by a lack of information on the effects of common land‐use practices. We evaluated the effects of moderate grazing by cattle (short‐duration, winter‐spring rotational grazing regime; 6–28 animal‐unit days/ha/year) on this tortoise by comparing two grazed and two ungrazed sites in the Western Rio Grande Plains, Texas ( U.S.A.), from April 1994 to October 1997. We made 132 captures of 106 individuals in the ungrazed pastures and 324 captures of 237 individuals in the grazed pastures. We also radiotracked 22 tortoises in the ungrazed pastures and 25 tortoises in the grazed pastures. Comparisons of relative abundance, body‐size distribution, age distribution, body mass, sex ratio, adult survival, proportion of juveniles, and growth rates revealed no differences ( p&gt; 0.05 for all parameters) between tortoises on grazed and ungrazed areas. Based on these results, we suggest that moderate grazing by cattle is not incompatible with maintenance of Texas tortoise populations. Our data were consistent with a general model of tortoise biogeography and tolerance of disturbance which suggests that Texas tortoises are tolerant to intermediate levels of disturbance. Generalities about the effect of cattle grazing on the four North American tortoises should be avoided unless they can be placed in the context of grazing regime, precipitation, habitat quality, and tortoise requirements.

Influence of cattle grazing on population density and species richness of granivorous birds (Emberizidae) in the arid plain of the Monte, Argentina

Cattle grazing is an important disturbance in the Monte plain, reducing grass biomass and rates of fruit setting. Grass seeds are the most important food for granivorous birds (Emberizidae) during winter. The objective of this study was to test whether granivorous bird populations (Emberizidae), grass seed production, and vegetation structure differed at sites with different intensities of grazing. Emberizid density and species richness were higher in the ungrazed site than in the two grazed paddocks. Seed abundance was also higher in ungrazed vs. grazed sites. Woody vegetation, that serve as safe nest sites, did not differ among treatments. Granivorous bird populations seemed to be affected by cattle grazing; however, the main mechanisms of this process remain unknown.

SOIL DEGRADATION RELATED TO OVERGRAZING IN THE SEMI-ARID SOUTHERN CALDENAL AREA OF ARGENTINA

The aim of the present study is to determine quantitatively the magnitude of the structural changes that occur in the soil during the degradation process affecting natural grassland in the semi-arid ecosystem of the southern area of the District of the Calden, Argentina. Topsoil horizons show a reduction in depth from 20 cm in ungrazed sites to 16 cm in grazed sites, mainly as a consequence of soil compression caused by animal hooves. Bulk density values in the first 5 cm of the profile in grazed sites are approximately 27% higher than those in ungrazed sites. Total porosity values in the top few centimeters are, on average, 17% lower in grazed sites, primarily due to the collapse of macropores (>50 μm) and larger mesopores (50-9 μm). Water retention curves for the three depths in the different patches reflect the changes in pore space distribution. Grazing causes a sharp increase in mechanical impedance-an average increment of 210% over ungrazed values in the first 10 cm of soil. There are marked differences in the degree of aggregation in grazed sites compared with ungrazed sites. The former show a lower quantity and density of roots in the top few centimeters of the profile. Changes are also evident in average root diameter as a result of vegetation substitution brought on by overgrazing. The lack of significant differences in soil physical properties in areas subject to different grazing intensities underscores the gravity of the problem caused by animal traffic, which poses a serious threat to the conservation and recovery of the grazed patches.

Antelope Bitterbrush Seed Production and Stand Age

Antelope bitterbrush (Purshia tridentata (Pursh) DC) is the most important browse species on many western mule deer (Odocoileus hemionus) ranges. Lack of antelope bitterbrush seedling recruitment is a critical problem, and therefore, the influence of livestock grazing on antelope bitterbrush seed production is an important issue. Seed production was compared in grazed and ungrazed communities during 1995 and 1996 at 2 locations in northeastern California and one location in northwestern Nevada. A system of seed traps was used to estimate seed production in relation to the size, age and grazing of antelope bitterbrush plants in the various stands. Antelope bitterbrush seed production was significantly (P less than or equal to 0.01) higher at one of the ungrazed sites. Significant (P less than or equal to 0.05) differences in shrub ages were also recorded between sites. DOI:10.2458/azu_jrm_v54i3_clements

Evapotranspiration in a Prairie Ecosystem

Grazing by ungulates is common in grasslands and may influence evapotranspiration (ET). The Bowen ratio energy balance method (BREB) was used to measure ET from grazed (GR) and ungrazed (UGR) tallgrass prairie sites in northeastern Kansas, USA. Yearling steers were stocked on the GR site from day of year (DOY) 128 to 202 in 1999, and ET data were collected from DOY 141 to 295. Grazing reduced ET by 28% between DOY 179 and 207; mean ET values were 3.6 (GR) and 5.0 mm d−1 (UGR). During that period, leaf area index (LAI) was an average of 78% lower on the GR site, and below‐normal precipitation kept soil dry near the surface; hence, transpiration and evaporation of water from soil decreased. Lower ET during that period, conserved soil water in the 0‐ to 0.30‐m profile on the GR site. Before that (e.g., DOY 152–179), ET was similar between treatments, despite an average 70% lower LAI on the GR site compared with the UGR site. Above‐normal precipitation during that period probably maintained high evaporation of water from soil, thereby compensating for reductions in transpiration (via LAI removal) on the GR site. Cumulative ET values during the 155‐d study were estimated at 526 and 494 mm on the UGR and GR sites, respectively. Thus, grazing reduced seasonal ET by 6.1%. Late in the study, ET was higher on the GR site, despite a lower LAI compared with the UGR site. Younger leaves in regrowth after grazing resulted in delayed senescence, causing higher ET on the GR site.

Effects of ungulate grazers on arbuscular mycorrhizal symbiosis and fungal community structure in tallgrass prairie

Complex interactions among mycorrhizal fungi, plants, and herbivores occur in grasslands. Grazing of aboveground vegetation may influence plants directly and indirectly through the alteration of mycorrhizal symbiosis and other below-ground processes, and mycorrhizae in turn can influence plant responses to defoliation. An understanding of these interactions is important to our understanding of the dynamics of plant and fungal communities and to the sound management and conservation of grassland ecosystems. In this study, the effects of grazing in tallgrass prairie on mycorrhizal colonization of plant roots, fungal community composition, and extraradical mycorrhizal hyphal (EMH) development were examined. In October 1994 and 1995 rhizosphere samples were taken at different topographical positions in tallgrass prairie sites grazed for several years by cattle at varying intensities, in ungrazed sites, and inside and outside permanent 25-m2 exclosures at each site. Spores of 19 species of AM fungi were encountered in these sites, and Glomus heterosporum was the most abundant species present. Moderate and intense grazing increased root colonization by mycorrhizal fungi in both years of this study. Similar root colonization levels inside and outside permanent exclosures in the ungrazed sites indicated no confounding effects of the exclosure structure itself. In 1995, EMH development was also increased under intense grazing. AM fungal species diversity (based on AM fungal spores present) decreased with grazing under both moderate and high grazer densities in both years. Different fungal species varied in abundance with topographical position, however topography did not significantly affect AM fungal spore species diversity, mycorrhizal root colonization or EMH development in either year. Although overall total spore density was unaffected by grazing intensity or soil type, several individual species increased or decreased in response to these factors. These results suggest that defoliation alters plant resources which stimulates greater development of mycorrhizal symbiosis. The shifts in fungal species composition and decrease in diversity with grazing also indicates that defoliation, or alteration of the soil microenvironment by grazers, favors certain species of grazing-adapted AM fungi that increase under grazed conditions. The high mycorrhizal dependency of many tallgrass prairie grasses and these results together suggest significant interactions between plant-grazer and plant-fungal relationships in tallgrass prairie. In addition to direct effects of herbivory, our results indicate that grazers may influence grassland plants indirectly through alterations in soil communities and in mycorrhizal symbiosis.

Effects of grazing on geophytes in Mediterranean vegetation

Abstract. The response of geophyte species diversity and frequency of individual geophyte species to cattle grazing was measured at 68 site pairs along fences separating ungrazed from grazed grassland and woodland on different geological formations in northern Israel. Over all site pairs, geophyte species density per 4 m2 was significantly greater in grazed (2.37) than in protected (1.96) sites of the same site pair. There was considerable variation between site pairs in the magnitude and in the direction of the grazing effect. Part of this variation could be explained by differences in site altitude and in geological formation. The positive effect of grazing on geophyte diversity was lower in sites with low productivity. Of 22 geophyte taxa for which sufficient data were available, nine indicated greater frequency in grazed sites compared to only two in ungrazed sites. In 11 other taxa the response was not consistent. A positive response to grazing was most common in geophytes with narrow leaves of the Iridaceae, Liliaceae and allied families. Conservation of the entire geophyte flora in Mediterranean vegetation requires livestock grazing at moderate to high intensities in parts of the area of each community, and light or no grazing in other parts.

Long‐term changes in the vegetation after the cessation of livestock grazing in Eucalyptus marginata (jarrah) woodland remnants

AbstractThis paper documents changes in the floristic composition of Eucalyptus marginata Donn (jarrah) woodlands over 7 years of recovery from continual, intensive livestock grazing. In remnants of native woodland left after agricultural clearing, which have been subjected to livestock grazing, comparisons were made between the floristics of fenced exclosure plots and open plots that continued to be grazed. The vegetation in nearby remnants, which had not been subjected to livestock grazing, was also surveyed. An initial increase in annual exotic pasture species after grazing relief was only temporary and highly influenced by fluctuations in annual climatic patterns, particularly rainfall distribution and abundance. Subsequent years saw a decrease in exotic annuals in exclosure plots and an increase in native perennials, in a trend towards becoming more floristically similar to the ungrazed sites. Germination of overstorey species was observed in the exclosure plots, however, development of seedlings and saplings was sparse. Results indicate that for jarrah woodland in southwestern Australia, natural regeneration is possible after the removal of livestock, with the return (within 6 years) of native species richness to levels similar to those found in ungrazed vegetation. Re‐establishment of cover, however, appears to take longer. The floristic dynamics are described in terms of a nonequilibrium model. Two vegetation states exist, degraded remnants with an understorey dominated by annual species, and ungrazed vegetation with an understorey dominated by perennial shrubs and herbs. The former state is maintained by continual heavy grazing by livestock. Upon relief from grazing, the vegetation undergoes a transition towards floristic similarity to ungrazed vegetation. After 6 years, vegetation change in the exclosure plots appears to be continuing and therefore it is still in transition.

ECOLOGY OF WILD EMMER WHEAT IN MEDITERRANEAN GRASSLANDS IN GALILEE

Aaronsohn in 1909 noted that Triticum dicoccoides was found mainly in rocky habitats. Recent research in Mediterranean grasslands in Galilee supports the hypothesis that rocks served as refuges from intensive grazing. Although proximity of rocks enhances early germination of Triticum, cattle grazing intensity is the major factor determining its abundance. At high grazing intensity, it is absent or survives only among rocks. At moderate grazing intensity it is common not only near rocks. In ungrazed sites it sometimes becomes dominant, but in the long term is often suppressed by perennial grasses. Fitness of Triticum plants in intensively grazed populations was only half that of plants in ungrazed populations, mainly because of damage to maturing ears. After grass fires, Triticum cover increased in ungrazed grasslands, as the cover of perennials was reduced. In ungrazed or lightly grazed grasslands, severe reductions of Triticum populations were observed during population eruptions of the Levant vole, foll...

Antelope bitterbrush seed production and stand age

Antelope bitterbrush (Purshia tridentata (Pursh) DC) is the most important browse species on many western mule deer (Odocoileus hemionus) ranges. Lack of antelope bitterbrush seedling recruitment is a critical problem, and therefore, the influence of livestock grazing on antelope bitterbrush seed production is an important issue. Seed production was compared in grazed and ungrazed communities during 1995 and 1996 at 2 locations in northeastern California and one location in northwestern Nevada. A system of seed traps was used to estimate seed production in relation to the size, age and grazing of antelope bitterbrush plants in the various stands. Antelope bitterbrush seed production was significantly (P less than or equal to 0.01) higher at one of the ungrazed sites. Significant (P less than or equal to 0.05) differences in shrub ages were also recorded between sites.

Livestock Effects on Reproduction of the Columbia Spotted Frog

We evaluated reproduction and recruitment of the Columbia spotted frog (Rana luteiventris Thompson) in 70 ponds used by beef cattle and in 57 ponds not used by beef cattle in northeast ern Oregon. No significant differences were detected in the num ber of egg masses or recently metamorphosed frogs in grazed and ungrazed sites. No pond characteristic measured could pre dict egg mass numbers, but percent aquatic vegetation and dis solved oxygen had some ability to predict recently metamorphosed frog numbers. Both variables explained 65% of the variability in recently metamorphosed frog numbers in grazed ponds. At ungrazed ponds, 4 additional variables (presence of fish, elevation, percent of rock, and conductivity) were required to achieve the same level of variability in predicting recently transformed frog abundance. The egg mass volume was larger at grazed than at ungrazed ponds suggesting that grazed ponds may have a greater food abundance or larger (older) individuals.

Western Ragweed Effects on Herbaceous Standing Crop in Great Plains Grasslands

Western ragweed [Ambrosia psilostachya DC. ], a major forb species in mixed and tallgrass prairies, is considered to have little value for cattle grazing but is an important food item for bobwhite quail [Colinus virgini anus ]. While often thought to be a strong increaser with grazing pressure, information on the actual relationship between western ragweed and grasses is contradictory. Our objectives were to 1) determine the effect of western ragweed on grass standing crop, and 2) determine the effect of vegetation type and grazing on survival and shoot morphology of western ragweed. Western ragweed did not appear to reduce grass standing crop. Instead, standing crop (40 to 620 kg ha - 1 ) and density (6 to 41 shoots m - 2 ) of western ragweed were positively related to grass and grassforb standing crop in mixed prairie. Standing crop of western ragweed was not related to grass standing crop in tallgrass prairie. Competitive thresholds for western ragweed in mixed and tallgrass prairies appear to be above the levels observed in this study. Density of western ragweed shoots decreased over the growing season under both grazed and ungrazed treatments. Survival of western ragweed shoots from June to September was greater in mixed prairie (81%) than in tallgrass prairie (63%) and was greater in ungrazed (76%) than grazed plots (68%). Western ragweed shoots weighed less per unit of height in tallgrass prairie. Western ragweed shoots in ungrazed plots were taller than shoots in grazed plots but weighed less per unit of height. These differences in shoot morphology are consistent with increased competition for light in tallgrass prairie and in ungrazed sites. Western ragweed may not directly reduce grass standing crop but, rather, increase only when grasses are reduced by other stresses such as improper grazing.

Morphological and Physiological Responses of Perennial Grasses to Long-term Grazing in the Pryor Mountains, Montana

We evaluated in situ the effects of long-term grazing (>100 y) on the morphological (i.e., shoot height, leaf blade length, width and angle) and physiological (i.e., gas exchange and water relations) responses of the dominant perennial grass species from arid lowlands and more mesic uplands of the Pryor Mountain Wild Horse Range (PMWHR) in Montana. Pseudoroegneria spicata, the most abundant grass in the lowland communities, had shorter vegetative shoot heights and leaf blade lengths and narrower leaves in plants from grazed than long-term ungrazed sites. Similarly, vegetative and reproductive shoot heights of Festuca idahoensis and Elymus lanceolatus, common upland grass species, were shorter in plants from grazed than ungrazed sites. Leaf lengths of these upland grasses also were shorter and less erect in plants from grazed sites than ungrazed sites. The physiological responses of the dominant grasses to grazing were not consistent between species or sampling dates. Overall, photosynthetic rates, stomatal conductances and xylem pressure potentials were the same in over 65% of the comparisons between plants from grazed and ungrazed sites and were higher in grazed sites in only 11 to 22% of the grazed-ungrazed comparisons. Collectively, our results indicate that long-term grazing of grasses by wild horses and other herbivores in the PMWHR has resulted in morphological modification, but has not substantively altered physiological function.

The effects of elk and cattle foraging on the vegetation, birds, and small mammals of the Bridge Creek Wildlife Area, Oregon

High densities of elk ( Cervus elaphus), especially when combined with cattle ( Bos taurus), may adversely affect local reforestation efforts and reduce forage availability. Few studies, however, have assessed the potential impacts of high densities of elk, combined with cattle, on biodiversity. We compared vegetation, bird, and small mammal diversity of three elk and cattle exclosures (ungrazed sites) to three grazed sites in the Blue Mountains of eastern Oregon. Shrub species richness was greater on ungrazed than grazed sites ( P=0.04). We found no differences in herbaceous vegetative cover, biomass, species richness, or diversity, bird abundance, species richness, or diversity between grazed and ungrazed sites. Small mammal abundance ( P≤0.01), species richness ( P≤0.01), and diversity ( P≤0.03) were greater on ungrazed than grazed sites. In this study, foraging by elk and cattle appears to be reducing shrub and small mammal biodiversity.