Human activities are changing wildfire regimes globally through ignition, spread of invasive species, fire suppression, and climate change. Because of this, ecosystems are experiencing novel fire regimes that may alter plant growth and patterns of succession. Annual growth rings are one metric that can track changes in tree and shrub growth patterns over time in response to changing fire frequency. In Chapter 1 we explored the effects of fire on resprouting native shrubs in the Mojave Desert. Fires are becoming increasingly frequent due to the spread of highly flammable invasive grasses in the region. We monitored growth and fruit production of Larrea tridentata D.C. (creosote bush) on burned and unburned transects from three independent 2005 wildfires. Even though creosote has a high fire mortality rate, we found that resprouting creosote produced 4.7 times the amount of fruit and had stems that grew nearly twice as fast compared to creosote in unburned areas. Our data suggest that creosote can resprout after fire and thrives in its growth rates and reproduction in post-fire environments. In Chapter 2 we used annual Basal Area Increment to investigate how fire suppression has altered facilitation and competition interactions through stages of succession in mixed aspen-conifer forests. We found that aspen had lower growth rates in mixed aspen-conifer stands compared to aspen dominant stands. We also found that aspen growing with an associated fir tree due to facilitation had increasingly lower growth rates over time than those growing independently. Fir trees in mixed stands were facilitated over time by associated aspen trees while fir trees growing in association and independently in aspen stands showed no statistical difference from each other but grew better than independent fir trees in mixed stands. Our data suggest that restoring a more frequent fire regime will balance competitive interactions between aspen and conifer in subalpine forests.

The landscapes of the Great Basin and Mojave Deserts are changing due to plant invasion. Highly flammable invasive grasses increase the size and frequency of fire causing a cascade of effects through the plant and animal communities. One of the most influential animal groups in desert systems is small mammals. We sought to learn how small mammals are impacted by fire and how their influence on the plant community differs between burned and unburned habitat. Small mammals did not have higher rates of mortality as a direct result of a controlled burn. In the Great Basin, there were short-term reductions in abundance, richness, and diversity of the small mammal community in burned plots. In the Mojave, species richness and diversity increased in burned plots shortly after fire and no abundance differences were detected. These results correspond with our prediction based on the dominant small mammal species at each site. Small mammals are primarily granivores; however, they also have strong impacts on the plant community via folivory. We tested for small mammal impacts on seedling survival in burned and unburned habitat. Small mammal access, burned vs. unburned habitat, and plant species were all important determinants of survival. Small mammals greatly reduced survival at both sites in burned and unburned habitat and often had a stronger impact in unburned than burned plots. Accounting for small mammal folivory may be a crucial step in successful post-fire rehabilitation. Finally, we used seed trays to test how small mammals influence the persistence of seed on the landscape. Small mammals reduced persistence of an invasive and native plant species in the Great Basin in 2012, yet a year later when small mammal abundance was reduced, no small mammal effect was observed. In the Mojave, persistence was reduced for the majority of species both years of the study. Small mammals did not appear to avoid seed of invasive plant species as we had predicted and may be important consumers reducing the reproductive potential of these invaders. If small mammals do prefer non-native seedlings over natives and are also consuming non-native seed, they may be greatly reducing the presence of non-natives both on the unburned landscape as well as after fire. Non-native consumption by small mammals could aid in the biotic resistance of these desert ecosystems. This research further enforces the important role that small mammals play as consumers, dispersers, and regulators of the plant community.

The introduction and establishment of exotic species can profoundly alter ecosystems. Two exotic species drastically changing the landscape of deserts in western North America are Bromus tectorum L. and Bromus rubens L. Through the buildup of biomass and slow decomposition rates in deserts these two exotic annual grasses can alter fire regimes that change the plant and animal community dynamics in the ecosystems. To better understand the ecological mechanisms that could restrict or alter the patterns of invasive plant establishment we established a replicated full factorial experiment in the Great Basin and Mojave Desert. The combinations of factors being manipulated are burned or intact plant communities, and presence or exclusion of small mammals. Generally invasive species establishment is thought to be a result of competitive superiority or lack of natural enemies, but if that is the case then why do not all invasive species establish and become highly abundant in their new ecosystems? To understand why some invasive species establish and others do not we monitored three dominant exotic species from the Great Basin and the Mojave Desert, B. tectorum, Halogeton glomeratus (M. Bieb.) C.A. Mey., and B. rubens. We observed that the presence of small mammals create a biotic resistance to B. tectorum, H. glomeratus, and B. rubens. This pattern was observed in both intact and burned plant communities; however, it was most prevalent in the burned plant communities. The strength of the biotic resistance on these invasive species varied between species and the years sampled. In deserts both plant and small mammal communities are tightly tied to precipitation. We wanted to understand how invasive species establishment is affected by small mammal presence after a fire disturbance, and manipulating total precipitation. Total precipitation was manipulated through three different treatments: 1) drought or 30% reduction of ambient precipitation; 2) ambient precipitation; 3) water addition or an increase of 30% ambient precipitation. We focused on B. rubens establishment in the Mojave Desert as our model organism by monitoring it beneath rain manipulation shelters nested in burned/intact and small mammal presence/absence full factorial plots. What we observed was that again small mammals created a biotic resistance on the density of B. rubens regardless of the burn or precipitation treatments. This biotic resistance also translated into decreasing B. rubens biomass and seed density. Under the drought and ambient precipitation treatments we found that small mammals kept the density and biomass equal but under increased precipitation the efficacy of biotic resistance on B. rubens density and biomass was lessened by the availability of the added water.

Following its introduction to North America in the late nineteenth century, Bromus tectorum L., an inbreeding invasive winter annual grass, has become dominant on millions of hectares of sagebrush steppe habitat throughout Intermountain Western North America. It appears that within the last 30-40 years, B. tectorum has expanded its range southward into the Mojave Desert and also into more climatically extreme salt desert environments. Previous research using microsatellite markers and experimental studies has suggested that lineages found in desert habitats are genetically distinct from those found in the sagebrush-steppe habitat and possess suites of traits that pre-adapt them to these environments. To provide additional support for our hypothesis that desert habitat-specific haplotypes dominate and are widely distributed across warm and salt desert habitats, we genotyped approximately 20 individuals from each of 39 B. tectorum populations from these habitats and adjacent sagebrush steppe habitats using 71 single nucleotide polymorphic (SNP) markers. Our data clearly demonstrate that populations throughout the Mojave Desert region, as well as in salt desert habitats further north, are dominated by a small number of closely related SNP haplotypes that belong to the desert clade. In contrast, populations from adjacent environments are largely dominated by haplotypes of the common clade, which is widely distributed throughout the North American sagebrush steppe. Populations across all habitats were usually dominated by 1-2 SNP haplotypes. This suggests that inbreeding B. tectorum lineages can often maintain their genetic integrity. It also explains the strong association between marker fingerprints and suites of adaptive traits in this species.

This archaeological and historical investigation focuses on the area in and around the town of Goffs, California, which was used for support and logistical facilities and had some association with combat divisions during the period. The central question concerns the nature and the role of the military units from 1942 to 1944. Was this site a a significant part of the World War II era DTC? C-AMA, and how did it relate to the whole? Efforts to answer this question included document research and extensive field investigation. The result is a more complete view of the wartime activites at Goffs and their relationship to the whole DTC/ C-AMA, other governmental agencies, and other organizations.

The Desert Solitaire curriculum was designed as a basis for exploring Edward Abbey's book, of the same name, in a high school field ecology class. Students read the book over a period of six weeks during the middle of the school year. Lessons were designed to aid students in exploring their home ecosystem, the Mojave Desert, via comparison with Arches National Monument as described in Desert Solitaire. This exploration fosters in students a sense of place and connection with their home environment. With little alteration, the curriculum can be used by students to examine their own ecosystem, even if it is not a desert. Furthermore, this curriculum can be used for delving into environmental issues, exploring environmental values and/or beliefs, or as an introduction to the genre of nature literature.

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.

This thesis is the culmination of a graduate research project involving a floristic survey of the lichens of the Spring Mountain National Recreation Area (SMNRA), Humboldt-Toiyabe National Forest, Nevada. The project was based on extensive collections made between 1997 and 2007 as part of an air pollution biomonitoring program and a baseline established by Larry St. Clair (BYU). The Spring Mountains are a sky island mountain range in the Mojave Desert located less than an hour northwest of Las Vegas. A floristic survey of the lichen communities in the Spring Mountains represents a major addition to our understanding of the lichen flora of the Mojave Desert, a poorly studied region in western North America. This thesis also compares the lichen flora of the SMNRA with other lichen floras of the Mojave Desert based on a literature survey of all the lichen studies conducted in the Mojave Desert. The SMNRA species list represents 58% of the 217 species in 68 genera reported for the Mojave Desert. This survey of all reported Mojave lichen species reveals several interesting interactions related to species diversity, substrate, and growth form distribution patterns. These interactions appear to be influenced by two general factors: Microhabitat conditions and available substrates – which are further defined by differences in geological substrates, occurrence and development of woody plant communities, and a combination of environmental factors – elevation, temperature, precipitation, and insolation. Drier and warmer habitats are generally dominated by crustose species with some, mostly smaller, foliose taxa in protected microhabitats usually with shaded or northern exposures. Fruticose species are generally lacking or sparse with smaller thalli when found in hot and dry habitats. All the fruticose species reported from the Mojave Desert sites were rare and had very small thalli. Many foliose and fruticose species, with larger, more complex thalli and thus greater surface area, are more susceptible to higher rates of water loss and therefore occur less frequently in extreme arid locations. The lichen communities in the Mojave Desert respond to sharp contrasts in microhabitat conditions with exposed, lower elevation sites having lower numbers of species along with more drought resistant growth forms – crustose and squamulose species. The Spring Mountains NRA, with high elevation mountains and well developed woody plant communities, accommodates a large variety of microhabitat conditions spread over a complex temperature and moisture gradient. These conditions have resulted in the highest species diversity (124 species in 48 genera) and the greatest number of foliose and corticolous species when compared with all of the other Mojave Desert lichen floras.

The impacts of mining are easily observable in the way they alter the terrain of landscapes, displace animals, and increase waste accumulation in an area. An unobservable impact and one that lasts a long time is by radioactive exposure in the environment. Specifically, this is a risk at uranium (U) mine sites which are expanding in number to accommodate the world’s growing energy needs, and even to accommodate weapons manufacturing. This paper analyses the impacts of an abandoned uranium mine on the local environment through measurements of Uranium concentration in soil, plants, and rocks. Transect sampling was used to collect 22 soil samples and 17 plant samples between 5 and 100m of the mine shaft. Uranium concentrations in soil and plant samples, digested with nitric acid, were measured with an Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES), and an X-ray Powder Diffraction (XRD) analysis was used to find the mineral contents of the rock samples. Satellite positions were associated with each sample, which allowed an effective spatial analysis of the Uranium concentration values. U values in soil ranged from 0 to 5.291ppm, with mean concentrations of 0.710 ppm, and U values in plants ranged from 0.0323 to 0.1121ppm with mean concentrations of 0.0558 ppm. A paired t-test determined that there was no spatial autocorrelation in U concentrations of plants and adjacent soils. The highest U concentration was found closest to the mine, peaking at ~7.3 meters from the mine, and low spatial variability occurs in U concentrations at greater than 10 meters from the mine. In comparison with other mines internationally, U concentrations at this study site were low, which may be indicative of a small operating mine, efficient clean-up, and transport mechanisms of U in desert environments.

Field guide -- Map -- Nature trail plant species -- Plant identification key -- Species test plot -- Climate -- Cloud identification -- Desert soils -- Tortoise station -- Animal track and pond.