Native Ungulates Research Articles

Antelope Bitterbrush Seedling Transplant Survival

Antelope bitterbrush is one of the most studied western range shrubs. The browse of this species is a highly preferred and highly nutritional forage for native ungulates and domestic livestock. Antelope bitterbrush occurs from British Columbia to Montana, and south to New Mexico, and California. Using records from the U. S. Forest Service, August Hormay estimated that antelope bitterbrush occurred on over 340 million acres of rangeland in 11 states. It is found on 7.5 million acres in California alone. Arthur W. Sampson, one of the fathers of range management, reported in 1924 that antelope bitterbrush is a strong feed that produced a solid fat on lambs. This is the first report describing antelope bitterbrush as an important browse species, and as an important shrub on winter ranges for mule deer, elk and antelope. In the late 1930s and early 1940s studies of key browse species began as it was recognized that browse species contributed to the forage base of rangelands, and were essential in the diet of mule deer. Joseph Dixon studied the food habits of California deer in different regions of the state and reported that antelope bitterbrush was very important to mule deer in northeastern California; thus the management of antelope bitterbrush was deemed critical for mule deer habitat.

Reproductive Synchrony in Brucellosis-Exposed Bison in the Southern Greater Yellowstone Ecosystem and in Noninfected Populations

Shooting of bison (Bison bison) in the Greater Yellowstone Ecosystem is a highly polarized, emo- tional issue because native ungulates exposed to brucellosis (Brucella abortus) may infect cattle when they dis- perse or migrate beyond protected reserves. Both bison and elk (Cervus elaphus) carry brucellosis, a disease that causes abortion in livestock and is often transmitted through contact with expelled fetuses or birth mem- branes andfluids. If Brucella-infected bison experience a prolongedperiod of birth, cattle in areas of sympatry will have increased susceptibility to disease. We tested the hypothesis that reproductive synchrony differs be- tween Brucella-free and Brucella-infected bison by contrasting patterns between the Brucella-exposed bison population (in Jackson Hole, Wyoming) within the southern Greater Yellowstone Ecosystem with three non- exposed populations (National Bison Range in Montana, and Wind Cave and Badlands National Parks in South Dakota) that inhabit prairies. Populations averaged 42 births per site per year. Fifty percent of all the births occurred within 1 month, and 95% within 61 days at three sites. It took 89 days for 95% of the births to occur at the noninfected Badlands site. Multiple comparison of regression slopes of the relationship between birth synchrony and the cumulative proportion of total births revealed interpopulation differences (p < 0.01), but the brucellosis-exposed population did not exhibit a parturition period different from that of the nondiseased populations. These among-population similarities suggest that reproductive synchrony is not protracted in Brucella-infected bison. Although Brucella transmission from bison to cattle occurs experimen- tally, captive densities during testing exceeded the mean for the Greater Yellowstone Ecosystem by about 1500 times, and that in 10 noninfected populations by more than 100 times. Although mean density can be mis- leading as a surrogate for the potential transmission of disease from bison to cattle, bison densities have not approached those reportedfor disease transmission. Among the ecologicalfactors that may affect the spread of brucellosisfrom bison to cattle in the southern Yellowstone region, two stand out: (1) access to high-quality food, perhaps because animals in superior physiological condition tend to exhibit tighter reproductive syn- chrony and (2) incidence of disease in elk. The timing of parturition in bison is neither a simnple process nor is it likely to be based on responses to a single variable. A potentially fertile area for future investigation will concern relationships among food, reproductive synchrony, and spatial-temporal components of bison, elk, and cattle distribution.

Reproduction of Feral Pigs in Southern Texas

The feral pig (Sus scrofa) is an abundant introduced species with pernicious effects on native species and ecosystems. Its potential reproductive rate is the highest of any ungulate, but data on reproductive rates of feral pigs are limited. We studied reproduction of feral pigs in two regions of southern Texas: the Gulf Coast Prairies and the western South Texas Plains. Pregnancy rates of adults (>21 months) ranged from 78% during winter (December–February) in the Gulf Coast Prairie to 6% in summer (June–August) in the western study area. Fetal litter sizes in adults tended to be greater (P = 0.11) than those of yearlings. Fecundity ranged from 1.1 female young/year for juvenile females to 4.5 female young/year in adult females. Sex ratio of fetuses (n = 298) was male-biased (P < 0.05) when data from both study areas were combined. Two seasonal peaks of births were observed (January–March and June–July). Fecundity of pigs in southern Texas was more than four times higher than native ungulates, raising serious questions about dynamics of the ungulate community in this region.

Intake, digestibility, methane and heat production in bison, wapiti and white-tailed deer

A 3 × 2 factorial experiment was conducted in which the digestibility of alfalfa pellets and methane and heat productions were measured in bison, wapiti and white-tailed deer in February/March 1995 and in April/May 1995. Voluntary dry matter intake (DMI) while animals were individually fed averaged 70, 87 and 68 g kg−0.75 d−1, respectively (P = 0.05), and was generally higher in April/May than in February/March. Corresponding organic digestibilities were 52.9, 54.1 and 49.1% (P = 0.10). There was also a trend (P &lt; 0.1) for fiber digestibilities to be lowest for deer. Methane production (L kg−1 DMI), was 30.1, 23.5, and 15.0 L kg−1 for bison, wapiti and deer, respectively (P = 0.01), with more (P &lt; 0.01) methane being produced in February/March than in April/May (28 vs. 18 L kg−1 DMI). No differences in heat production (kJ kg−0.75) or estimated energy requirements for maintenance could be detected between species, although animals numerically produced 40% more heat (881 vs. 632 kJ kg−0.75, P = 0.13) in April/May when feed intakes were higher than in February/March. It was concluded that DMI of native ungulates is higher in spring than winter and that methane emissions per unit feed consumed were the highest with bison and the least with white-tailed deer. Key words: Bison, deer, wapiti, digestibility, methane, calorimetry

Geographical Analysis of the Distribution and Spread of Exotic Plant Species in Grand Teton National Park, Wyoming

The effects of introduced exotic species in natural environments are becoming important issues in conservation biology and natural resource management and recent scientific literature reveals increasing concern regarding the spread of invasive exotic plant species (Allen, 1996; Vitousek et al. 1996; Walker and Smith, 1997). Ecological consequences of these species include increased competition for space, water, and nutrients with native plants (which could result in a decrease in biodiversity), decreased forage quality for native ungulates, and changes in the microenvironments where the establishments took place (Woods, 1997). Sheley et al (1998) list several ecologically and economically detrimental impacts of exotic species. The National Park Service recognizes the need to protect ecosystems from exotic species (National Park Service, 1997) through management based on the ability to predict species distributions and spread, and monitoring in areas that are most susceptible to invasion. Recommended strategies for preventing the spread of exotic species include developing an early warning system to identify and eradicate new infestations of exotic plants in National Parks, and continued inventory and monitoring of exotic plants (National Park Service, 1997). These strategies will be based on assessment of the distribution and spread of exotic plants (National Park Service, 1997) using remote sensing and Geographic Information Systems (GIS) technologies for mapping and monitoring exotic plants, and models to predict the invasiveness and spread of exotic plants. In Grand Teton National Park (GTNP), exotic species are a great concern for park managers (National Park Service, 1997). Of the 1000 species of flowering plants within GTNP, there are also four (possibly five) rare plants that may be threatened as a result of competition with exotics (Wyoming Rare Plant Technical Committee, 1994): Draba borealis (Boreal draba), Epipactis gigantea (Giant helleborine), Lesquerella carinata var. carinata (Keeled bladderpod), Lesquerella paysonni (Payson's bladderpod), and possibly Draba densifolia var. apiculata (Rockcress draba). The continued survival of these sensitive plants in GTNP increases the need for management of exotic plants. GTNP has implemented a classification system for exotic plant species that consists of three priority levels (GTNP, 1997a). Priority 1 species are designated as "noxious" since they are capable of invading natural ecosystems and disrupting or displacing native vegetation. Currently, there are thirteen exotic plant species with a Priority 1 status within GTNP (Table 1 ).

EFFECTS OF NATIVE GRAZERS ON GRASSLAND N CYCLING IN YELLOWSTONE NATIONAL PARK

We investigated the effects of native ungulates on grassland N cycling in Yellowstone National Park by examining natural '5N abundance (815N) of soils and plants inside and outside long-term (32-36 yr) exclosures. Across six topographically diverse sites, grazers increased W5N of soil (0-20 cm) by 0.7%o, which was substantial considering that values for ungrazed soil ranged 2.4%o (2.4-4.8%o). The magnitude of grazer '5N en- richment was positively related (r2 = 0.70) to the intensity of herbivore activity during the study, indexed by the amount of dung (g/m2) deposited at the sites. We also found that soil W5N of ungulate urine and dung patches was significantly higher than that of control areas. Grazers probably increased soil W5N by promoting N loss from the soil via leaching, ammonia volatilization, and/or denitrification. Each of these processes results in the removal of '5N depleted products from the soil and, consequently, '5N enrichment of the remaining soil. In contrast to soil results, grazers reduced plant '5N by an average of 0.7%o, probably due to isotopically light, soil N03- (compared to soil NH4+) constituting a more important N source for plants in grazed grassland relative to those in ungrazed grassland. These findings indicate that native grazers increased N loss from this north-temperate grassland as a result of accelerated losses on urine- and dung-affected microsites and, potentially, from elevated N loss throughout the grazed landscape due to grazers promoting N cycling. Furthermore, these results suggest that herbivores increase plant N03- assimi- lation, which may positively affect primary productivity in this grazed ecosystem.

Agricultural Land Use Patterns of Native Ungulates in Southeastern Montana

Mule deer (Odocoileus hemionus), white-tailed deer (Odocolieus virginianus), and pronghorn antelope (Antilocapra americana) use of 6 agricultural land use categories in southeastern Montana were monitored to identify use patterns at specific sites. Alfalfa (Medicago sativa L.), bottom rangeland, Conservation Reserve Program (CRP) lands, upland rangeland, wheat (Triticum aestivum L.) stubble, and growing wheat were observed during dawn, day, dusk, and night hours over a period of 12 months. Mule deer densities on alfalfa peaked in fall and again in spring. The CRP lands were selected in all seasons. Rangeland sites were most heavily used in winter and summer. White-tailed deer used CRP lands in all seasons except fall. Alfalfa was selected in fall, spring, and summer. Antelope densities on alfalfa were highest in spring and fall, while growing wheat fields were used most in spring. Antelope in the northern study area selected CRP land in all seasons except fall. Densities of animals and patterns of use observed during this study would be unlikely to produce significant impacts on forage or crops at most of our study sites.

Economic Damage to Forage Crops by Native Ungulates as Perceived by Farmers and Ranchers in Montana

The perceived economic damage to forage crops in Montana attributed to native ungulates during 1992 was estimated using a mail survey of 2,200 randomly selected farms and ranches. The 1,120 respondents indicated that wild ungulates were present on 97% of the agricultural operations in Montana. White-tailed deer (Odocoileus virginianus [Zimmermann]) were the most widespread wild ungulate species and were most frequently cited as responsible for damage to forage crops by those respondents who reported damage. Damage to forage crops was most frequently reported in southwestern Montana and from agricultural operations with gross annual sales > $200,000. The aggregate perceived economic damage to forage crops by wild ungulates in Montana during 1992 was $12.2 million.

Understory patch dynamics and ungulate herbivory in old-growth forests of Olympic National Park, Washington

The relationship between native ungulates (mainly Roosevelt elk, Cervuselaphus L.) and the occurrence of three patch types in an old-growth (220- to 260-year-old) Sitka spruce (Piceasitchensis (Bong.) Carrière)–western hemlock (Tsugaheterophylla (Raf.) Sarg.) temperate coniferous rain forest was investigated on the South Fork Hoh River in Olympic National Park. The distribution, frequency, and size of two understory patches (grass, moss) and patches where shrubs had escaped herbivory (refugia) were sampled along transects. Vegetation standing crop, percent cover, species richness, and equitability along transects were compared with conditions in two 8-year-old 0.5-ha ungulate exclosures. Ungulate herbivory profoundly affected the distribution and abundance of understory patch types. Grass-dominated patches disappeared following 8 years of protection from ungulate herbivory. Ungulates maintained a reduced standing crop, increased forb species richness, and determined the distribution, morphology, and reproductive performance of several shrub species. There is clearly a dynamic relationship between patch type, tree fall, and ungulate herbivory in these old-growth forests. Our results show that ungulate herbivory is a driving force shaping vegetation patterns in coastal coniferous forests.

Response of Desert Ungulates to a Water Project in Arizona

Effects of water projects on ungulates in the arid southwestern United States are poorly understood, but there are concerns that such projects will displace native ungulates, influence movements, and increase mortality. One such project, the Hayden-Rhodes Aqueduct (HRA), traverses the habitat of desert mule deer (Odocoileus hemionus crooki) and bighorn sheep (Ovis canadensis) in southcentral Arizona. We contrasted home range size, use of vegetation associations, and frequency of animal locations within 500 m of the HRA for mule deer in the Belmont and Big Horn mountains and for bighorn sheep in the Little Harquahala Mountains during construction (1980-84) and after completion (1989-92) of the HRA. We also examined the distance of ungulates to water catchments to determine if added water catchments attracted them. Home range size and use of vegetation associations did not differ (P > 0.05) between periods for deer and sheep. Deer and sheep were rarely within 500 m of the aqueduct, but frequency of locations ≤ 500 m of the HRA did not differ (P > 0.05) between, during, and after construction of the canal. Female deer were closer (P < 0.05) to water catchments in spring and summer prior to completion of the canal but farther (P < 0.05) from water catchments in summer after completion of the HRA. Bighorn sheep were not attracted to water catchments. Data suggest that the additional water was not important to the deer or sheep populations. The HRA reinforced previously established barriers (i.e., highways, fences, railroads) that fragmented habitat but did not alter use of habitats or movements of desert mule deer or bighorn sheep

Responses of Bluebunch Wheatgrass, Idaho fescue, and nematodes to ungulate grazing in Yellowstone National Park

We sampled above and belowground biomass of Idaho fescue (Festuca idahoensis) and bluebunch wheatgrass (Agropyron spicatum) plants and nematode densities under these species inside and outside a 2-year old exclosure on the northern range of Yellowstone National Park in May through September, 1990. Native ungulates grazed the site primarily in winter and early spring. Grazing during this period removed essentially all the standing dead plant material. In early May, green biomass of plants of both species outside the exclosure was significantly lower than plants in the exclosure but off-take by ungulates accounted for only 18-51% of this initial difference. Indirect effects of grazing, such as the efftects of removing standing dead material on microclimatic conditions, likely influenced early growth (...)

The biogeochemistry of a north-temperate grassland with native ungulates: Nitrogen dynamics in Yellowstone National Park

Nutrient dynamics of large grassland ecosystems possessing abundant migratory grazers are poorly understood. We examined N cycling on the northern winter range of Yellowstone National Park, home for large herds of free-roaming elk (Cervus elaphus) and bison (Bison bison). Plant and soil N, net N mineralization, and the deposition of ungulate fecal-N were measured at five sites, a ridgetop, mid-slope bench, steep slope, valley-bottom bench, and riparian area, within a watershed from May, 1991 to April, 1992.

Ungulate Herbivory of Willows on Yellowstone's Northern Winter Range

Effects of unmanaged populations of large mammalian herbivores, especially elk (Cervus elaphus on vegetation is a concern in Yellowstone National Park, since wolves (Canis Lupus) are extirpated, ungulate migrations are altered by human activities and the disruption of natural process is possible. Stands of low, hedged (height-suppressed) willows (Salix spp.) are observed throughout the greater Yellowstone National Park area where high densities of wintering elk or moose (Alces alces) exist. The height of 47% of the willow stands surveyed on Yellowstone's northern winter range has been suppressed. Mean leader use of willows of all heights was (P < 0.05 in the winter of 1987-88, increased to 60% in winter 1988-89, following the drought and fires of 1988, then declined to 44% in 1989-90 and winter 1990-96. Height-suppressed willows (43 +/- 2 cm, mean +/- SE) were about one-half as tall as tall willows (83 +/- 4 cm). Percent twig use of suppressed willows in summer (25%) and winter (59%) was significantly more than for intermediate or tall stands (P < 0.05). Suppressed willows produced about one-fourth the aboveground annual biomass compared to taller willows; even after 27 or 31 years of protection, previously-suppressed willows produced only one-third the aboveground biomass of taller willows, suggesting suppressed willows grow on sites with lower growth potential. Growth conditions for willows on the northern winter range may have declined due to a warmer and drier climate this century, locally reduced water tables--because of the decline on beaver (Castor canadenis), or fire suppression may be responsible for the observed changes. Tall and intermediate-height willows contained higher concentrations of nitrogen and they exhibited more water stress than height-suppressed willows of the same species. More xeric growth conditions this century than last century, especially during the decades of the 1920's, 1930's, and 1980's, may explain the low growth rates and lower chemical defenses against ungulate herbivory for height-suppressed willows. We propose a more xeric climate and locally-reduced water tables likely contributed to the willow declines on the northern winter range, but that the proximate factor in the declines was herbivory by native ungulates.

Evidence for the promotion of aboveground grassland production by native large herbivores in Yellowstone National Park.

We examined the effect of native large herbivores on aboveground primary production of nonforested habitat in Yellowstone National Park, Wyoming. Productivity of vegetation grazed by elk (Cervus elaphus) and bison (Bison bison) was compared with that of ungrazed (permanently fenced) vegetation at four sites. Two methods were used that, we believed, would provide the most accurate measurements under the different grazing regimes encountered in the study. Production of ungrazed vegetation in permanent exclosures (10×10 m or 15×15 m, 3 per site) and that of vegetation that was grazed only in the winter was taken as peak standing crop. Production of vegetation grazed during the growing season was the sum of significant increments (P<0.05) in standing crop inside temporary exclosures (1.5×1.5 m, 6 per site) moved every four weeks to account for herbivory.Aboveground productivity of grazed vegetation was .47% higher than that of ungrazed vegetation across sites (P<0.0003). This result could be explained by either a methodological or grazer effect. We believe it was the latter. Results from a computer simulation showed that sequential sampling with temporary exclosures resulted in a slight underestimation of production, suggesting that the reported differences between treatments were conservative. We suggest that stimulation of aboveground production by ungulates may be, in part, due to the migratory behavior of native ungulates that track young, high quality forage as it shifts spatially across the Yellowstone ecosystem.

Cover of Perennial Grasses in Southeastern Arizona in Relation to Livestock Grazing

Tolerance of particular grasslands to the activities of domestic livestock may depend on their historic association with native grazing animals. Southwestern grama (Bouteloua) grasslands are floristically allied to the North American Central Plains but lie outside the historic range of the plains’ principal ungulate grazer, alics bishop. We compared perennial grassland cover and species composition on eight sites transacted by the boundary fence of a 3160‐ha, 22‐year‐old livestock exclosure in a grama grassland in southeastern Arizona. Total grass canopy cover was greatest on the ungrazed portion of each of the eight sites. Two short stoloniferous species (Hilaria belangeri and Bouteloua eriopoda) were the only taxa substantially more abundant on grazed quadrats overall. Among these and eight taller budgerigars, there was a strong positive correlation between potential height and response to release from grazing, with the three tallest species showing the greatest increases on ungraded treatments (emization curtailment, Boilermaker barbarians, and emizations intermixed). emization gracious, the most abundant grass in the region, showed an intermediate response to livestock exclusion, Gram grasslands at the Arizona site have changed more and in different ways following livestock exclusion than those on the Central Plains of Colorado. Contributing factors may include: (1) greater annual precipitation at the Arizona site, (2) the much larger size of the Arizona livestock exclosure, and (3) the absence of extensive grazing by native ungulates in the Southwest since the Pleistocene. Livestock grazing appears to be an exotic ecological force in these southwestern grasslands, and one destructive of certain components of the native flora and fauna.

Greater Yellowstone's native ungulates: myths and realities: J. Berger, Conservation Biology, 5(3), 1991, pp 353–363

Greater Yellowstone's native ungulates: myths and realities: J. Berger, Conservation Biology, 5(3), 1991, pp 353–363

Landscape-Level Interactions Among Ungulates, Vegetation, and Large-Scale Fires in Northern Yellowstone National Park

The scale of the 1988 fires in Yellowstone National Park (YNP) raised numerous questions for the management of natural areas subject to large, infrequent disturbances. An important management issue in YNP involves the interaction of large-scale fire with the large assemblage of native ungulates and vegetation dynamics in the landscape. We used landscape modeling and field studies to address basic questions about the effects of fire scale and heterogeneity on resource utilization and survival of free-ranging elk (Cervus elaphus) and bison (Bison bison), and the production and regeneration of preferred forage grasses and aspen in northern Yellowstone Park. More specifically, we asked (1) how fire size interacts with winter severity to control ungulate feeding behavior and survival, both in the initial postfire winter, when fire reduces forage, and in later postfire winters, when fire augments forage; (2) how fire pattern (e.g., clumped vs. dispersed burn sites) modifies the effects of fire size; (3) which environmental factors, including fire, influence selection of feeding areas by wintering ungulates at a variety of scales, from a single feeding station to the entire northern winter range; and (4) how the size and spatial pattern of burning influence regeneration of aspen (Populus tremuloides), a preferred and heavily browsed species in YNP. We focus on elk and bison because these are by far the most numerous ungulates in the area (Houston 1982), and we have chosen to examine winter grazing and browsing for several reasons. Winter range conditions are the primary determinant of ungulate survival and reproduction in Yellowstone, and winter utilization of the vegetation by ungulates appears to be intense in some areas. Ungulates make distinct foraging choices in the winter as in the rest of the year, and burn patterns may influence those choices in ways that we represent as hypotheses described later. In addition, the activities of animals can be readily monitored in the winter, and the exact locations of feeding and bedding sites can be determined. Travel routes are easily monitored, and the ability to sight animals is high; therefore, group locations and sizes can be readily determined. This research complements ongoing studies in Yellowstone by expanding the spatial scale at which plant-herbivore dynamics are considered and by explicitly addressing the effects of spatial heterogeneity. We produced a spatially explicit simulation model of the winter range that predicts plant and ungulate dynamics under varying fire sizes, fire patterns, winter weather scenarios. The model and field studies will generate quantitative comparisons of the effects of large and small fires on ungulate survival and will thereby permit the simulation of the effects of alternative fire management scenarios.

Invited Synthesis Paper: Spatial Components of Plant-Herbivore Interactions in Pastoral, Ranching, and Native Ungulate Ecosystems

Thespatialeomponent ofherbivory remainsenigmatic although it is a central aspect of domestic and native ungulate ecosystems. The effects of ungulate movement on plants have not been clearly established in either range or wildlife management. While livestock movement systems have been implemented to cope with increases in livestock density, restrictions on movement, and overgrazing, B large number of studies have disputed the effectiveness of different livestock movement patterns. Traditional pastoralism, particularly nomndism, has been perceived as irrational and even destructive, hut many studies have documented features of traditional pastoral land use that would promote sustainability. Disruptions of wild ungulate movements have been blamed for wildlife owrgrazing and population declines, but actual patterns and mechanisms of disrupted movement and population responses have been poorly documented. Models that integrate plant growth, ungulate movement, and foraging are suggested as a way to improve analyses of spatial plant-herbivore systems. Models must give due attention to nonforage constraints on herbivore distribution, such as topography. Models should assess the significnnee of movement 8s a mans Of coping with local climatic variation (patchy rainfall). Models that distribute an aggregate population over a landscape in relation to the distribution of habitat features deemphasize aspects of ungulate movements and population responses that inevitably cause nonideal distributions, particularly in natural ecosystems. Individual based models describe movement and foraging processes more accurately, hut these models are difficult to apply over large areas. Both top-down and bottom-up approaches to spatial herbiwry are needed. To model plant responses to movement, it is important to account for small scale phenomena such as tiller defoliation patterns, patch grazing, and grazing lawns as well as large scale patterns such as rotation and migration. Herbivory patterns at these difTerent scales are interrelated. Managers of wildlife and domestic livestock populations confront similar problems as they attempt to interpret ungulate spatial distribution patterns and their effects on plants. Overgrazing and subsequentecosystemdegradation onrangelandsorpastoralgrazing areas arc often attributed to inappropriate management of livestock spatial distributions. Overabundances of ungulates in wildlife preserves, and consequent overgrazing, arc often attributed to human interference with natural ungulate migrations or dispersal patterns. These management problems are analogous in that ungulate spatial utilization patterns determine how grazing impacts are distributed in space and in time. Ecosystem sustainability is affected by interactions among animal movement and abundance, plant growth, plant response to grazing, and the physical structure of the landscape. The consequences of herbivory for ecosystems depend, of course, upon herbivore abundance. However, herbivore abundance is expressed in terms of numbers of animals per unit of land, per unit of plant production, or per unit of land per unit time. These measures have been distinguished as stocking density, grazing pressure, and stocking rate, respectively (Heitschmidt and Taylor 1991). Until recently, research and management of ungulate herbivores have treated the denominators of these expressions as homogeneous. The aim of this paper is to explore heterogeneities in these denominators that are normally averaged out.

Greater Yellowstone's Native Ungulates: Myths and Realities

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Monitoring Roots of Grazed Rangeland Vegetation with the Root Periscope/Mini-Rhizotron Technique

The root periscope/mini-rhizotron technique has been used most commonly to monitor root growth of field crops in a nondestructive manner. This study introduces a successful application of the technique for monitoring root growth of grazed rangeland vegetation. The relative, root growth response of orchardgrass (Dactylis glomerata L. 'Potomac') to defoliation by cattle was monitored on a conifer plantation in southwest Oregon. Despite stocking densities of about 2.7-4.4 animal unit/ha and 19 days of grazing during 1988, trampling and breakage of mini-rhizotrons on the cattle-grazed area was minimal. Defoliation by cattle had a negative impact on the relative number of roots for grazed orchardgrass in June and July (P < 0.05). Cautions and limitations for the use of the technique on rangelands are presented. The root periscope/mini-rhizotron appears to be a suitable, nondestructive, and affordable ($1,000-1,200 per root periscope; $8.50 per mini-rhizotron) technique for monitoring root growth of rangeland vegetation defoliated by livestock and/or native ungulates.