Date of Award


Degree Type


Degree Name

Master of Science (MS)



First Advisor

Dr. Rebecca Drenovsky


Biological soil crust communities (biocrusts) growing on gypsum soils have been well- documented for their prolific appearance and rich diversity of lichens and bryophytes. However, studies characterizing gypsum biocrusts have primarily occurred outside of the U.S., most of which lack comparisons to other soil types. We conducted intensive field surveys to evaluate the cover and frequency of biocrust functional groups and moss species on gypsum and non-gypsum soils in the U.S. regions with the most extensive gypsum outcrops, the northern Chihuahuan and eastern Mojave Deserts. We employed canonical correspondence analysis (CCA) to relate the observed differences in biocrust abundance and composition across soil types to distinct environmental and soil variables. Additionally, we assessed species richness of biocrust mosses on gypsum versus non-gypsum soils, as well as in the Chihuahuan versus Mojave Deserts. Our results support previous observations that biocrusts are especially abundant on gypsum soils but that these differences are likely due to gypsum’s profuse dark algal (predominantly cyanobacteria-forming) rather than lichen and moss biocrusts. Biocrust functional groups did not exhibit associations with environmental and soil variables. However, moss species appear to be strongly influenced by environmental variables and exhibited differential preferences for substrate parent material. Moss species richness was greater on gypsum soils and, surprisingly, in the hottest and driest North American Desert, the Mojave. Differences in species richness across deserts was strongly correlated to mean annual and seasonal temperatures, as well as mean winter precipitation. Overall, our data suggest that soil, environmental, and climate conditions all play important roles in the ecology of biocrusts, specifically moss diversity and distribution, in the northern Chihuahuan and eastern Mojave Deserts of the U.S. More importantly, we emphasize that gypsum soils of the U.S. are unique refugia for moss-forming biocrusts.

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