Desert Experimental Range Research Articles

Interaction Assessment: A modeling tool for predicting population dynamics from field data

Interaction Assessment (INTASS) is a field and analytic methodology for constructing population dynamics models. Because data collected in generating a model for one species comprise much of the information needed for other species, a small increase in effort can result in simultaneous expressions for the dynamics of multiple species. These expressions can be used to simulate whole community responses to environmental change, including management actions. Since publication of the most recent paper in this series, the INTASS methodology has undergone a large number of developments. These include the use of conceptual models to direct field and modeling efforts and incorporation of an information theoretic approach to model selection. We review these modifications and additions, applying them to a population of Sitka black-tailed deer ( Odocoilius hemionis) in Alaska and to cheatgrass ( Bromus tectorum) at the Desert Experimental Range in Utah. In both cases, useful information about the species’ ecology and population trends was ascertained. INTASS is portable across a wide range of taxa, habitats and management situations.

SEM study of phytoliths produced by grasses indigenous to the desert experimental range in southwestern utah

The USDA Desert Experimental Range Station located in southwestern Utah has been conducting an ongoing investigation into the effects of grazing on the ecology of the region, The study reported herein is a preliminary effort to determine if phytolith analysis can be used to gain insight into the ecology of the region prior to the 60 year period over which records have been kept.Phytoliths are solid deposits of silicon dioxide that form at specific intracellular and extracellular locations in many plant taxa. Grasses produce phytoliths with morphological characteristics diagnostic of their taxa. When a plant dies, its phytoliths resist decomposition thereby becoming micro-fossils of the plant that produced them. Micro-fossil phytoliths provide archaeobotanical and ecological information because they remain in the same soil horizon at which decay occured. In this study phytoliths produced by four grasses indigenous to the Experimental Range were analyzed. Phytoliths extracted from soil samples of different grazing treatments at the Range were then analyzed to determine if any similar to those produced by the four grasses could be identified in the soil. If so, then phytolith analysis could prove to be a viable research tool for those studying the paleoecology of the Range.

Effects of grazing and drought on population dynamics of salt desert shrub species on the Desert Experimental Range, Utah

We examined natality, mortality, and population turnover of dominant salt desert shrub species under different seasons (winter vs. spring) and intensities (light vs. heavy) of grazing during a drought period on the USDA Forest Service Desert Experimental Range in southwestern Utah. Species responses were more predictable from their life history and physiological traits than from past responses to grazing alone. Heavy or spring grazing increased mortality of Artemisia spinescens, a cool-season shrub susceptible to past grazing, and of Sporobolus cryptandrus and Atriplex confertifolia , a C4 grass and shrub, respectively, that had increased under this grazing regime in the past. Light or winter grazing during this period increased survival and natality of S. cryptandrus, and of Ceratoides lanata, a shrub that had decreased in density but increased in cover under past grazing. Population turnover rates were generally positive for A. spinescens, but were highly negative for A. confertifolia in all but the heavy spring grazing treatment. A. confertifolia had exhibited high mortality during past droughts. C. lanata exhibited little population change reflecting past trends. Generally positive rates of turnover for the two grasses, S. cryptandrus and O. hymenoides, paralleled past trends, except in the spring-heavy treatment which had highly negative turnover rates. In a comparison of grass vs. shrub dominated vegetation types, C. lanata had higher mortality in grass dominated plots; O. hymenoides had higher mortality in shrub dominated plots. Both S. cryptandrus and O. hymenoides exhibited low or negative turnover rates for grazed plots within the shrub dominated type. Overall, light to moderate grazing and the removal of livestock before active physiological growth of cool season species had the least negative effects on population dynamics during a two-year drought period. This grazing regime increased survival or natality of certain species.

Melanistic Pronghorn Fawns on the Desert Experimental Range, Utah

Melanistic Pronghorn Fawns on the Desert Experimental Range, Utah

Pronghorn Reactions to Winter Sheep Grazing, Plant Communities, and Topography in the Great Basin

The winter distribution of pronghorn over a 142-km2 area on the Desert Experimental Range was significantly related to sheep grazing during the current winter, presence of black sagebrush, and topographic characteristics. Even moderate sheep use during the dormant period left grazing units relatively unfavorable for pronghorn until spring regrowth-at least on ranges where key pronghorn forage plants were in short supply. Winter use areas preferred by pronghorn were above the valley bottoms in rolling to broken topography where black sagebrush communities were evident. Movement characteristics of pronghorn have allowed many of them to readily locate rested grazing units, and, therefore, avoid severe dietary competition with sheep. The Great Basin and other parts of the Intermountain West contain about 16 million ha of low-shrub cold desert. Most of these lands are publicly owned, and their primary use has traditionally been the grazing of sheep in winter and cattle in various seasons. In the last decade or so land managers have intensified efforts to consider the needs of wild animals, and require specific information to consistently make good management decisions. Information is available on pronghorn diets, water requirements, and predator losses (Beale and Holmgren 1975, Beale and Smith 1970, Beale and Smith 1973), but no intensive study has been accomplished in the Great Basin region to document the effects of livestock grazing systems on pronghorn (Antilocapra americana) populations Kindschy et al. 1978). Neither have the impact of other uses of the low-shrub desert on pronghorn been well documented for the Great Basin. A study to probe the effects of winter sheep grazing and certain environmental factors on pronghorn distribution wasconducted on the USDA Forest Service Desert Experimental Range near Milford, Utah, during the winters of 1976-81. Pronghorns thrive best on ranges with a diversity of grass-forbshrub communities (Autenrieth 1978), but are widely adaptable to different forage conditions across the total range of the species. The severity of competition between pronghorns and domestic livestock appears to vary greatly with differences in species of livestock, season of the year, and plant species available to the foraging ruminants (Salwasser 1980, Yoakum 1980). Although pronghorn habitat has mainly been manipulated by livestock grazing, many proposed energy, mineral, and defense activities threaten severe habitat disruptions. Winter ranges are often especially critical for pronghorn and are of particular concern (Kindschy et al. 1978). When the most important plants in the pronghorn's diet are a minor component of the vegetation, widespread surface disturbances or intensive sheep grazing of all available habitat could result in increased winter mortality for the pronghorn. The size and stability of pronghorn winter home ranges appear to be important in the animal's ability to adapt to newly created unfavorable habitat situations. Bayless (1969) found the pronghorn's winter home range to average 10-1 1 kM2, but one-half of the Authors are principal range scientist, Intermountain Forest and Range Experiment Station, Shrub Sciences Laboratory, Provo, Utah 84601; and wildlife biologist, Utah Division of Wildlife Resources, Cedar City, Utah 84720. Authors thank range technician John Kinney for his initiative and consistency of observation which made this study possible. Manuscript received Jan. 21, 1983. animals observed shifted home range at least once during the winter. This suggests that pronghorns may be flexible in their selection and use of wintering areas, although Howard et al. (1980) reported pronghorn avoided rough, broken terrain.

Factors Influencing Development of Cryptogamic Soil Crusts in Utah Deserts

The relationofsomephysiallandchemicalsoilcharncteristicsto cryptogamic crust development was determined from sites in semidesert regions of southern Utah. The effects of grazing on eryptogamic crust development also wasexamined. Electrical conductivity, percentage silt, and soil phosphorus were found to he correlated with well-developed cryptogamic crusts. Both total cryptognmic cover and the number of cryptogamic species decreased under grazing pressure. Themsnagement ofmngelands, especially in arid regions, would bestrengthened by understanding the role of cryptogamic crusts and considering them in range management decisions. The vascular plants of many semidesert areas furnish a scant ground cover of discrete and widely spaced units. Between the plants are rather extensive open spaces exposed to the elements. Where soils are gravelly, a pavement of pebbles provides protection from erosive forces of wind and water. Another factor, less obvious but ofimportance in the controloferosionin theinterspaces, particularly where the gravel pavement is weak or absent, is a community of nonvascular or cryptogamic plants that grow upon or immediately beneath the soil surface. Where well established and undisturbed by trampling, the cryptogams form a recognizable crust (Fig. I). Algae are the primary components of these crusts, but in some environments, themorevisiblemacroscopiclichensand mossesare common members of the cryptogamic cover (Anderson and Rushforth 1977, Kleiner and Harper 1972). Even though they are small and often inconspicuous, cryptogamic species play an important role in soil stabilization in semideserts (Fletcher and Martin 1942). Algal filaments, fungal mycelia, and tissues of lichensand mosses are present throughout the surface few millimeters of many semidesert soils (Anderson and Rushforth 1977, Hunt and Durrell 1966). Where lichens and mosses grow in abundance, the stability of the soil surface is readily apparent, but the less obvious algae, especially the filamentous algae, are probably more effective in binding the surface soil particles (Anantani and Marathe 1974; Durrelland Shields 196l).Thethickgelatinoussheathsthatencase some of the algal species probably add strength and toughness to the felt-like web of filaments among the soil particles in the surface I or 2 millimeters of a well-established algal crust. Cryptogamic crusts are common in the arid regions of the westn and more importantly, lichen-free grasslands could be maintained through continous moderate to heavy grazing, suggesting cryptogams can be used to evaluate grassland management practices. Little has been done to incorporate the information known about soil crusts into range management considerations. It seems likely that our ability to manage ranges, especially in arid regions, would be strengthened by such an inclusion. The purposes of this study are two-fold: first, we seek to determine the relations of some physical and chemical soil factors to crust development, and second, we desire to evaluate the effect of grazing on cryptogamic soils crusts. Study Areas Five areas in the southern part of Utah were selected for study (Fig. 4). All are characterized by low precipitation, hot summers, and cold winters. The Desert Experimental Range (DER) of the USDA-Forest Service is located in western Utah and isthedriest of all the areas considered: precipitation averages I5 cm annually. Two study areas are along the Hurricane Fault in extreme southwestern Utah near St. George and Hurricane, which receive about 19 and 22 cm average annual precipitation, respectively. Virginia Park in Canyonlands National Park in southeastern Utah is the wettest site, receiving about 30 cm of annual precipitation, mainly during the warm season. The temperature extremes for all five areas are similar over the past IO years. Maximums are around 4CPC and minimums -14OC or lower (Holmgren 1973). Quite different vascular communities prevail at the study sites. Species of low shrubstypical ofthecolddesertdominatethestands at the DER. Hilaria (galleta) and Boutelouo (blue grama) are the most common grasses. Ephedra (Mormon tea) and Larrea (creosotebush) are the most common vascular plants at St. George, while Ephedra and Petalonyx (sandpaper plant) are the dominant vascular species at Hurricane. Hi/aria and Sripa (needlegrass) grasslands characterize Virginia Park. An additional collection was made north of Black Rock, Utah, in Atriplex (saltbush) and Chrysothomnus (rabbitbrush) communities. The St. George and Hurricane study sites are on gypsum outcrops and have sparse vascular cover and heavy cryptogamic cover of algae, lichens, and intermingled mosses characteristic of gypsiferous soils.

Arid land monitoring using Landsat albedo difference images

The Landsat albedo, or percentage of incoming radiation reflected from the ground in the wavelength range of 0.5 μm to 1.1 μm, is calculated from an equation using the Landsat digital brightness values and solar irradiance values, and correcting for atmospheric scattering, multispectral scanner calibration, and sun angle. The albedo calculated for each pixel is used to create an albedo image, whose grey scale is proportional to the albedo. Differencing sequential registered images and mapping selected values of the difference is used to create quantitative maps of increased or decreased albedo values of the terrain. All maps and other output products are in black and white rather than color, thus making the method quite economical. Decreases of albedo in arid regions may indicate improvement of land quality; increases may indicate degradation. Tests of the albedo difference mapping method in the Desert Experimental Range in southwestern Utah (a cold desert with little long-term terrain change) for a four-year period show that mapped changes can be correlated with erosion from flash floods, increased or decreased soil moisture, and increases or decreases in the density of desert vegetation, both perennial shrubs and annual plants. All terrain changes identified in this test were related to variations in precipitation. Although further tests of this method in hot deserts showing severe “desertification” are needed, the method is nevertheless recommended for experimental use in monitoring terrain change in other arid and semiarid regions of the world.

Survival Patterns of Major Perennials in Salt Desert Shrub Communities of Southwestern Utah

Chart quadrat records periodically taken at the Desert Experimental Range in southwestern Utah over 34 years were examined for evidence of establishment and survival of eight major perennial plant species. A set of seedlings that became established in 1935-37 were followed until 1968-70. Relatively few individuals have died since the second year after establishment. There were few significant differences between the survival of plants in the grazed versus ungrazed plots. West et al. (1979) recently reviewed the relevant literature and noted the dearth of demographic data dealing with perennial plants in arid and semiarid environments. Further comparative studies describing survivorship curves and discussion of how mortality and longevity vary with environmental perturbations seem appropriate. Unfortunately, there exist few sources of longterm data complete enough to perform analyses like those West et al. (1979) did on 2 1 + years of pantograph records taken on the U.S. Sheep Station in southeastern Idaho. There exist, however, at other research stations periodic pantograph or chart quadrat records and stand maps that could be of some use in exploring these issues. The following is an attempt to use such data from the Desert Experiment Range (DER) in southwestern Utah.

Comparison of Fecal, Rumen and Utilization Methods for Ascertaining Pronghorn Diets

Fourteen male pronghorn (Antilocapra americana), two in each of seven spring and summer months, were killed to obtain rumen and fecal matter for comparing methods of determining diets. They came from a herd confined to the Desert Experimental Range in southwestern Utah. Animals were killed only after they had completed their early morning grazing period. Plant material was removed from the rumens and rectums, fresh feces were collected from the feeding site, and forage utilization and production estimates were made there. Diets as indicated by the four data sources-rumen, intestinal feces, site feces, and utiiizationvaried with individual animals from close to little agreement, a not unexpected result in view of food availability and selection. Fewer plant species were identified by fecal analysis than were found in the rumen; even fewer species were recorded by utilization estimates. This indicates that fecal analysis may be less accurate than rumen data but more so than those based on plant utilization. Validation tests of the fecal method conducted with mule deer (Odocoileus hemionus) fed known diets showed substantial differences with individual species in the amounts fed and the amounts indicated by fecal analysis. Only in the case of the single grass species fed was there close agreement; browse and forb species differed greatly. Effective management of wild ruminants and their habitat depends upon a knowledge of plants selected and the composition of the diet at each season. All methods for determining animal diets have disadvantages. Analyses of rumen contents necessitate sacrificing animals unless fistulated animals are available, a costly and often troublesome procedure. Moreover, biased estimates may result from rumen samples because plants have different rates of digestibility and disappearance from the rumen. Utilization estimates, usually ocular, are subject to observer error and personal biases. Utilization is difficult to detect when use is light, as it often is with game animals; and when more than one herbivore is present it may not be possible to separate their effects. There are limited oppdrtunities for observing wild animals feeding at close range. In dense vegetation, determining the plant being utilized is nearly impossible. Use of tamed animals can minimize some of these difficulties, but they provide limited and possibily unrepresentative sampling. Fecal analysis is increasingly advocated to avoid the disadvantages of other methods for determining diets of free

Nutritional Quality of Summer Diets of Pronghorn Antelopes in Utah

Between 1 May and 30 September, 1969 and 1970, plants eaten by pronghorns (Antilocapra americana) on the Awapa Plateau and at the Desert Experimental Range in Utah were collected at triweekly intervals and subjected to chemical analysis for protein, phosphorus, and digestibility. Diets were determined by estimating percentage of utilization and quantity of vegetation available at locations where pronghorns were seen feeding. Crude protein values varied from 10 to 22 percent; digestibility coefficients were between 71 and 77 percent. Lowest levels of dietary crude protein were observed at the Desert Experimental Range, but the highest values were recorded there as well. Overall, there was little difference in digestibility of forage at the two locations, but differences that were found favored animals at the Desert Range location. Both protein content and digestibility declined more rapidly as the season advanced on the Awapa Plateau; at the Desert station, both nutritional parameters were erratic in response to the amount and timing of summer precipitation. There is nothing in the data to suggest nutritional constraints in the forage available to antelopes during summer at either location. J. WILDL. MANAGE. 38(4):792-798 One of the reasons postulated for the present low productivity of pronghorns in many desert areas is that the vegetation now found on these ranges is deficient in one or more critical nutrients. This factor was cited by western game departments as a prime suspect for the failure of pronghorns to produce as well as their biological capacity seemed to indicate (Foree 1959). Little is known of the nutritional qualities of forage used by pronghorns. The little information that is available comes from nutritional assessments for domestic livestock and, on the deserts of western Utah, these apply only to winter months. During the summer months, a wide variety of plants are available that are not present during the winter, and these have not been investigated as to chemical make-up or

Three Noteworthy Cacti of Southwestern Utah

In the spring of 1939 and 1940 Dr. Fred A. Barkley collected some unusual cacti in southwestern Utah in the vicinity of the Desert Experimental Range west of Milford. These cacti were locally known as Opuntia fragilis. Dr. Barkley called the author's attention to them and at the same time further collections were made by Drs. Selar Hutchings and Gordon Marsh of the U.S. Desert Experimental Range Staff.