COVER AND COMPOSITION OF BIOLOGICAL SOIL CRUST VARY AS A FUNCTION OF DISTURBANCE DUE TO LIVESTOCK IN A SONORAN DESERT GRASSLAND

Abstract

Cryptic organisms are increasingly recognized for their influence on ecosystem function and services. Biological soil crusts are communities of aggregated soil particles, bryophytes, lichens, cyanobacteria, and other microbes that influence arid ecosystem function by provisioning soil nutrients, increasing soil water capacity, and reducing soil erosion. Biocrusts are broadly sensitive to mechanical disturbance, but knowledge gaps persist in our understanding of disturbance impacts to cover and composition of biocrusts. Because of their sensitivity to disturbance and importance in arid ecosystem function, biocrusts may provide important insight into ecological theory of disturbance in arid ecosystems. I assessed cover and composition of biocrusts across a gradient of disturbance by livestock in a Sonoran Desert grassland in southern Arizona. I found reductions in biocrust cover and shifts in biocrust communities under greater use by livestock. I argue that biocrust communities are negatively impacted by livestock use, but that some biocrust morphotypes may be more resilient to, or benefit from, some level of disturbance. This work provides new data about the composition and distribution of biocrusts in southern Arizona and contributes new insights about the potential impacts of livestock on these important elements of dryland ecosystems.