Southern Arizona was once described as a "sea of grass" extending across the four major valleys, the Sulphur Spring Valley, the San Pedro Valley, the San Simon Valley and the San Bernardino Valley. But today the majority of that land is covered with desert shrubs like mesquite, leaving little to none of the natural grasses that once dominated these valleys. By the late 1800s Americans were flocking to southern Arizona to take advantage of some of the lushest grasslands the United States had to offer. Yet today we can find very little of these grasslands remaining, and so the image of this once productive land has been long forgotten. This thesis/creative project takes an in-depth look at what the land in Cochise County, Arizona once was, what it has become, and what happened to cause these drastic changes. It looks at the four major theories as to what caused these changes. The first of which is the overgrazing of cattle through the cattle boom of the late 1800s. The second is the effect of climactic events like drought and an increase in aridity over time. The third is the encroachment of what was thought to be non-native mesquite, which choked out the natural grasses. And the fourth and final theory is that the overarching suppression of fire by settlers allowed desert shrubs to expand their ranges into the grasslands. Through historical records like newspaper articles, photo archives, land surveys, military travel journals, census data, weather records as well as prior research works and interviews with researchers, conservationists and ranchers, a history of these lands is presented to show the major turning points in the lands' use and determine what led to their deterioration.

Biological soil crusts (biocrust) are photosynthetic communities of organisms forming in the top millimeters of unvegetated soil. Because soil crusts contribute several ecosystem services to the areas they inhabit, their loss under anthropogenic pressure has negative ecological consequences. There is a considerable interest in developing technologies for biocrust restoration such as biocrust nurseries to grow viable inoculum and the optimization of techniques for field deployment of this inoculum. For the latter, knowledge of the natural rates of biocrust dispersal is needed. Lateral dispersal can be based on self-propelled motility by component microbes, or on passive transport through propagule entrainment in runoff water or wind currents, all of which remain to be assessed. I focused my research on determining the capacity of biocrust for lateral self-propelled dispersal. Over the course of one year, I set up two greenhouse experiments where sterile soil substrates were inoculated with biocrusts and where the lateral advancement of biocrust and their cyanobacteria was monitored using time-course photography, discrete determination of soil chlorophyll a concentration, and microscopic observations. Appropriate uninoculated controls were also set up and monitored. These experiments confirm that cyanobacterial biological soil crusts are capable of laterally expanding when provided with presumably optimal watering regime similar to field conditions and moderate temperatures. The maximum temperatures of Sonoran Desert summer (up to 42 °C), exacerbated in the greenhouse setting (48 °C), caused a loss of biomass and the cessation of lateral dispersal, which resumed as temperature decreased. In 8 independent experiments, biocrust communities advanced laterally at an average rate of 2 cm per month, which is half the maximal rate possible based on the instantaneous speed of gliding motility of the cyanobacterium Microcoleus vaginatus. In a span of three months, populations of M. vaginatus, M. steenstrupii, and Scytonema spp. advanced 1 cm/month on average. The advancing crust front was found to be preferentially composed of hormogonia (differentiated, fast-gliding propagules of cyanobacteria). Having established the potential for laterally self-propelled community dispersal (without wind or runoff contributions) will help inform restoration efforts by proposing minimal inoculum size and optimal distance between inoculum patches.