Currently the size and frequency of wildfires are increasing at a global scale, including arid ecosystems that exhibit great sensitivity to disturbance. Fire effects on plant pollination and reproductive success in deserts are largely unknown. Plant dependence on animal pollinators for reproduction can increase the risk of reproductive failure if pollination services are hindered or lost. Species that depend on few taxonomically related pollinator species are expected to be most negatively affected by disturbances that disrupt pollination interactions. To assess fire and isolation effects on reproductive success in desert plant communities, and how wildfire influences the pollination success of generalist and specialist pollinated plants, the number of flowers, fruits, and viable seeds produced by plants surviving in burned and unburned desert landscapes were compared. Fire increased flower production for wind and generalist pollinated plants, and did not affect specialist plant flower production. Increases may be associated with positive physiological responses exhibited by plants surviving in burned areas. Fire did not affect pollination services. Wildfire effects on fruit production were neutral or positive, and overall seed:ovule ratios varied by 3% or less in burned and unburned areas for each pollination strategy. Increasing isolation within burned areas did not affect fruit production for generalist or specialist pollinated plants, suggesting that pollination services are functional across expansive burned desert landscapes. Annual reproductive output varied between years in burned and unburned areas, and shifts likely resulted from variation in annual precipitation patterns. Reductions in landscape reproductive output may be partially compensated by increased per plant fruit and seed production and maintaining pollinator services across burned landscapes, providing native shrub communities the possibility to naturally recover from fire disturbances. Habitat disturbances can influence plant interactions with herbivores, in addition to pollinators. To understand how fire and ungulate herbivory affect reproductive success of specialist pollinated desert plants, reproductive effort, floral herbivory, and pollinator visitation and success, were compared for Yucca baccata, and Yucca brevifolia in burned and unburned areas of the Mojave Desert. Fire increased Y. baccata flowering from 12% to 22% of plants in burned areas, but had no effect on the number of flowers or fruits produced per plant. Fruit set and pollinator collection failed at all sampled Y. baccata individuals, while fire and herbivory had no effect on Y. brevifolia flower, fruit, and pollinator collection. Herbivores consumed 50% and 67% of floral stalks produced by Y. baccata in unburned and burned areas. Herbivores pose a clear threat to successful sexual reproduction for Y. baccata. Removal of ungulate herbivores during important flowering periods may still result in failed fruit and seed production if local pollinator reserves have been drastically reduced or lost.

<p dir="ltr">The origins and deposition of nitrate in dust traps in Mojave Desert are examined in this thesis. Two main hypotheses are tested: (1) most of the dust in the traps comes from local soil, implying that the nitrate content is primarily derived from the soil; and (2) wet deposition is the primary source of nitrate found in the environments, implying that precipitation processes play an important role in nitrate accumulation. To test these hypotheses, we collected data from 11 dust trap from locations in of the US Geological Survey's long-term investigation of dust composition and influx rates. Dust and soil samples were analyzed for ions to determine their origins and the contributions of local vs distant sources. Our findings show that the fraction of soil-derived nitrate (<i>f</i>_soilNO₃^-) is consistently low at all traps, hardly reaching 0.03, whereas the atmospheric nitrate percentage (<i>f</i>_atmNO₃^-) is usually close to or equal to 1. This shows that atmospheric sources play a substantial role in the nitrate levels detected in dust traps. Nitrate contributions are also significantly influenced by sedimentary and geological settings, such as the distinctions between alluvium and playa regions. Playas, which are composed of silt and clay, may have higher nitrate concentrations than alluvial plains, indicating that external dust inputs are significant. The second hypothesis's results show that nitrate deposition in the study area is primarily from dry sources, with dry deposition values ranging from 0.68 to 10.84 NO₃⁻/kg/ha/yr, averaging 4.12 NO₃⁻/kg/ha/yr, and wet deposition values averaging 1.09 NO₃⁻/kg/ha/yr. This observation challenges the hypothesis that wet deposition is the primary source of nitrate. The dominance of dry deposition is further supported by low amounts of precipitation and a weak correlation between precipitation and dust deposition. This study concludes that although local soil has a role in nitrate levels in dust traps in the study site, it is not the primary source, external sources and dry deposition account for the majority of nitrate in the dustpan</p>

This study is about the impacts of the transportation of low level radioactive waste (LLRW) on American Indians. The terms American Indians, Native Americans, and Indians are used interchangeably throughout this report to refer to people who are members of tribes in the United States. The information contained in this report is valuable to non -Indian individuals, communities, and governments as well as to the tribes and the U.S. Department of Energy/Nevada Operations Office (DOE/NV) for which it was prepared. Many of the individuals who agreed to participate in this study asked if their non -Indian neighbors were also being given the opportunity to share their views and perspectives on the transportation of LLRW near and through their neighborhoods. Although this study was designed to include only Native Americans, it can serve as a model for additional studies in non –Indian communities. American Indian tribes have a unique status as sovereign nations within the U.S., and this study was designed to address that relationship.This study includes an assessment of social and cultural impacts. One type of impact assessment concerns the estimation and communication of risks associated with potentially dangerous technologies or substances. Such an assessment, a technological "risk assessment," is generally conducted by natural or physical scientists and focuses on the probability and magnitude of various scenarios through time (Wolfe 1988). The specialists who conduct the assessment believe their estimates reflect the "real risks" of a technology or project because the estimates were made using scientific calculations. This study is not a risk assessment. Instead, this study pays attention to the public perceptions of impacts and risks. Like other social scientists, the researchers and American Indian partners who designed and conducted this study focus on public perceptions and frame the discussions in terms of locally defined values and concerns.This study involves 29 tribes and subgroups and is therefore very complex. Every effort has been made to present information systematically to help the reader make sense of what is being presented. Information about the tribes is presented in the same order throughout the report.

In the late 1970s, Southern California Edison Company proposed the construction of a 500 Kilovolt transmission line from Buckeye, Arizona (just west of Phoenix) to the Devers substation near Banning California. The proposed routes crossed the traditional territory of numerous Native American groups such as the Cahuilla, Chemehuevi Southern Paiutes, Cocopah, Mojave, Maricopa, O’Odham, Quechan, and Yavapai. As required by the National Environmental Policy Act, an environmental impact assessment was conducted to understand potential impacts this project could have on human and natural resources. For the first time since the passage of NEPA, Native American concerns were fully considered. This report presents the findings of the first Native American social impact assessment in the United States. This report presents contemporary Native American values that were pertinent to planning, construction, operation, and maintenance of high voltage generation and transmission facilities. The ethnographic study also considered the following aspects: (a) determine if, where, and in what manner such values were relevant to the Devers Palo Verde study area, (b) define differing levels of significance that Native Americans assigned to geographical points, zones, or issues within the subject study area exhibiting such values, (c) assign appropriate sensitivity ratings to the pertinent points, zones, or issues of significance and rank such points, zones, and issues from highest to lowest, explain what actions might constitute varying degrees, kinds of impact to those points, zones, or issues, and (e) provide recommendations for mitigation of negative impacts to those points, zones, or issues.

This project examined the potential impacts that construction of the Western Transmission System of the Allen-Warner Valley Energy System would have on the ethnographic and historic resources of the Mojave Desert area. The Western Transmission System of the Allen-Warner Valley Energy System project consisted of two 500-kilovolt transmission lines extending from Southern California Edison Company’s Eldorado Substation in southern Nevada westward across the Mojave Desert to Lugo Substation in Victorville, California. The ethnographic component of this study included the identification of culturally affiliated Native American groups and extensive field investigations which focused on ethnohistory and ethnogeography of the study area. The ethnographic study also documented Native American recommendations for mitigation by Southern California Edison Company of potential adverse impacts that the project had on Native American values and resources.

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.