Relationships of exotic plant invasions with biological soil crust, desert pavement, and soil carbon in the eastern Mojave Desert
Creators: name: DeCorte, Adria 
Publisher: name: University of Nevada, Las Vegas
Year: 2011

description: In a matter of 50 years, exotic annual plants have become widespread in the Mojave Desert, contributing to drastic landscape changes such as those caused by recent fires. Invasions by exotics threaten native Mojave Desert plant communities by altering community functions (e.g. fire regimes) and by reducing plant diversity. Because it is not practical, or even possible, to eradicate these exotics, developing effective prevention techniques is the key to controlling these invasions. 
This thesis used a greenhouse experiment, a field experiment, and a correlational field study to examine the affect soil surface types have on the establishment of three exotic plant species in the Lake Mead National Recreation Area of the eastern Mojave Desert. The species studied were Bromus rubens, Schismus spp., and Brassica tournefortii, and the soil surface types were biological soil crust, desert pavement, and areas free of rock mantle and living crust that are referred to as "open." Also examined were the effects that carbon addition and disturbance have on the establishment of these species. 
The results, analyzed using analysis of variance models, showed a correlation between carbon addition and the reduction of density and biomass in all three exotic species studied. In the field experiment, Bromus had a 69% reduction in density and a 93% reduction in biomass when carbon was added to the soil, and Schismus had an almost 100% reduction in density and biomass with carbon addition. In the greenhouse, carbon addition almost entirely eliminated Brassica germination, and Schismus density decreased by 49% on open surfaces and 65% on crust. 
Disturbance by hand-raking had no significant effect on establishment, and establishment varied by surface type with mixed results. At the field experiment site, where establishment on biological soil crust was compared to that on desert pavement, there was 83% more Bromus on crust than on pavement, but Schismus showed no significant correlation with surface type. In the greenhouse, where establishment on crust and pavement was compared to that on open surface, there was higher overall establishment on open surfaces. Schismus had the strongest response, with 63% higher density on open than crust and 87% higher density on open than pavement. Brassica had 36% higher density on open than crust or pavement. 
When plant community data from the correlational field study were analyzed using analysis of variance models, plant cover was higher on open sites than biological soil crusts and higher on crusts than pavement. Both open sites and crusts had higher species diversity than pavement. Multivariate community analyses showed that there were significant differences in annual plant community composition on crust at each of the sites surveyed. On the field experiment treatment plots, there was a significant difference between community composition for interactions between surface type and carbon addition and between surface type and disturbance. 
Protection of biological soil crust and desert pavement in conjunction with carbon addition could serve as useful tools for limiting the spread of invasive species in the Mojave Desert. These two surface types, pavement especially, exhibited lower exotic establishment than that on open surfaces. Using carbon addition to reduce soil fertility was overall successful at reducing invasive plant establishment. Disturbance results contradicted the literature's suggestions that disturbance is correlated with exotic establishment, a possible result of the short duration of the study. 
These findings are expected to contribute novel information to the broader understanding of these factors in arid lands as well as to provide information applicable for local land managers tasked with protecting desert soil surfaces and minimizing the impacts of exotic species.