Thesis (M.S.)--Brigham Young University. Dept. of Plant and Animal Sciences, 2005. / Includes bibliographical references (p. 14-18).

The purpose of this study was to provide basic ecological information on an important but little studied major vegetation type through autecological investigations of the dominant species. Data include climate and soils where this species occurs, root distribution, phenology and growth, seed germination requirements and seedling survival. Percent ground cover provided by blackbrush and other dominant plants as well as the composition of herbaceous understory vegetation was presented. Leaf and stem anatomy of blackbrush revealed features typical of desert shrub species with stem splitting appearing to be a characteristic of this species. Blackbrush is characterized as a poor forage species of low palatability. Nutrient content analysis provided data on ether extract, carotene, phosphorus, acid detergent fiber, crude protein, and lignin. Nutrient deficiencies occur during the winter when blackbrush ranges are grazed by domestic livestock. Brush beating or same similar method which will remove the old woody material from the plants was proposed as a method of increasing the forage quality without changing the entire community as is done with burning.

Coleogyne ramosissima Torr. (blackbrush) and Atriplex confertifolia [Torr. & Frem.] Wats. (shadscale) are cold desert shrubs from different families that often grow together in the Great Basin and the Colorado Plateau in the life zone between 800 and 2000 m elevation. Tissue and seeds from the two species were collected from several localities. Metabolic heat and carbon dioxide production rates were measured with calorespirometry on tissue from field-grown plants and on seedlings at temperatures from 5 to 35°C at 5°C intervals. Blackbrush adapts to higher temperatures earlier than does shadscale, and once it has adjusted to higher temperatures, anabolic rates keep rising with increasing temperature while for shadscale rates flatten out or drop off between 25 and 35°C. Both species are metabolically adapted to temperatures during the growth season determined by the historical rainfall pattern.

The purpose of this study was to provide data on responses of Angora goats and blackbrush (Coleogyne ramosissima) to a biological manipulation program. Blackbrush utilization levels averaged 30, 16, and 6 percent (545, 367, and 147 kg p er hectare) for the heavily, moderately, and lightly browsed pastures, respectively; removal rates of 77, 38, and 19 percent (1164, 582, and 291 kg per hectare) were projected. Statistically significant differences in body weight loss (P=0.052) were noted for goats browsing in different replications. Goats lost an average of 14 and 19 percent of body weight in replications one and two, respectively. Differential weight loss app eared to be related to variable crude protein levels in blackbrush twigs. Small, but statistically significant differences were noted between replications for crude protein (P:0.002) and phosphorus (P=0.019) content in blackbrush twigs. Crude protein content averaged 4.9 and 4.4 percent for replications one and two, respectively; phosphorus content averaged 0.18 and 0.15 percent for replications one and two, respectively. No statistically significant differences in plant production were noted among stocking rates; this was primarily a result of the low utilization levels. Site (replications) affected plant response (P:0.135), and terminal branches produced more current season's growth than did basal branches (P:0.162).

Domestic goats were used to modify the growth form of blackbrush, a spinescent shrub occurring in nearly monospecific stands on several million hectares of rangeland in the southwestern United States. The objective of this research was to evaluate goat browsing as a means of improving these rangelands for cattle. Winter goat browsing stimulated spring twig growth from basal and axillary buds which resulted in increased production. Twig production by heavily browsed plants (>95 percent removal of current season's twigs) was a function of precipitation, soil depth, branch location on the plant, and period of rest after browsing. As precipitation doubled, production increased by a factor of 1.9. Twig production by plants growing on deep soils (71 cm) was 1.9 times that by plants growing on shallow soils (39 cm). Older branches growing on the outer edges of blackbrush plants (terminal branches) produced 4.6 times more current season's twigs than sprouts and young branches (basal branches) growing within the shrub canopy. Heavily browsed plants increased twig production by a factor of 3.6 relative to control plants, and production remained at this level, even after four consecutive years of browsing. Stocking intensities of 2.4 animal-unit-months·hectare-1 were required to achieve utilization levels of 80 percent in blackbrush pastures. Annual twig production declined with rest from browsing. However, plants which were browsed and subsequently rested for two years yielded an aggregate 1.6 times more available forage than plants which were browsed on a yearly basis. This was due to an accumulation of twigs ranging in age from one to three years. Browsing also improved the apparent nutritional quality of blackbrush twigs. Current season's twigs contained more crude protein (6.5 versus 4.6 percent), phosphorus (0.10 versus 0.08 percent), and in vitro digestible dry matter (48 versus 38 percent) than older twigs. Current season's twigs from basal branches contained more crude protein (6.1 versus 5.7 percent) and in vitro digestible dry matter (44 versus 41 percent) than those from terminal branches. The palatability of current season's twigs to goats and cattle was lower, however, than that of older twigs, presumably due to their higher tannin levels. Within individual blackbrush plants, current season's twigs from terminal branches were higher in tannins than those from basal branches. Rest from browsing resulted in decreased tannin levels due to a decrease in the proportion of current season's to older twigs. Goats and cattle tended to prefer older twigs to current season's twigs, and current season's twigs from basal branches to those from terminal branches. The occurrence and allocation of tannins within blackbrush support hypotheses dealing with the elaboration and allocation of phyto-chemicals as defense mechanisms countering herbivory. Esophageally fistulated goats (does and kids) browsing in pastures where forage consisted primarily of current season's twigs consumed diets with more crude protein, in vitro digestible dry matter, and tannins than goats browsing in pastures where forage consisted primarily of older twigs. They also lost less weight. Does initially consumed diets higher, but later consumed diets lower in crude protein than those consumed by kids. Kids consumed diets with more in vitro digestible dry matter, but lost more weight than does. No statistically significant differences in weight response were recorded for cattle browsing in pastures which were, and were not, previously browsed by goats. However, the average heifer in previously unbrowsed pastures consumed 1.9 times more protein supplement than her counterpart in previously browsed pastures.

Climate change and exotic plant invasions are significant anthropogenic threats to desert community structure and resilience . In the Mojave Desert, the invasive grass red brome (Bromusrubens L) is increasing fire frequency and extent in response to climatic factors. The resilience of this ecosystem will be affected by how plant and animal communities respond to fire. To better understand these dynamics, we studied the environmental factors underlying changes in invasive grass fire regimes in the Mojave Desert and its structural and functional effects on plant and animal communities. Following fire, reestablishment of native vegetation can be preempted by repeated burning associated with the abundant exotic grass red brome. Red brome density is correlated with various climate and landscape variables, but to establish causality, we experimentally assessed germination and growth of red brome. Red brome responded positively to fall precipitation, finer-textured soils, fertile-islands soils, and soils from burned landscapes. Red brome germination is maximized in wet fall periods when adequate water and optimal temperatures overlap . To evaluate landscape responses of pre- and post-fire plant communities and the potential for repeated burning we analyzed vegetation greenness (NDVI) data from 1985-2011 in response to temperature and precipitation. Landscape analysis indicated that the dominance of exotic grasses increases on post-fire landscapes. Following wet fall and winter seasons, high red brome productivity increases fire potential. Without mitigation, the establishment of an invasive-plant-driven fire regime is likely and may drive state transitions from arid shrublands to arid annual grasslands. Potential revegetation of post-fire landscapes will depend at least in part upon the physiological response of surviving vegetation to post-fire landscapes. Plant physiological responses to post-fire landscapes were generally neutral or positive, suggesting that revegetation of post-fire landscapes is not precluded by resource loss associated with fire and may even be enhanced by post-fire conditions. This will likely translate to increased reproductive potential of surviving plants. Alterations to small mammal populations will likely play a role in the reestablishment of vegetation (both native and exotics) as small mammals have strong top-down effects in arid ecosystems. Diversity and species richness responded negatively to burned landscapes as Merriam's kangaroo rat (Dipodomys merriami) increased in abundance while other species practically disappeared from burned landscapes. Merriam's kangaroo rat affects propagule sources through direct consumption, and seed dispersal. Increases in abundance and dominance of Merriam's kangaroo rat will likely alter plant recruitment.