Biological Soil Crusts: Ecological Roles and Effects of Disturbance in Desert Systems

Abstract: Biological soil crusts are composed of an assemblage of species of cyanobacteria, lichens, mosses, and fungi. In many desert ecosystems, they fulfill several critical ecological functions in areas where vascular plant growth is limited due to low moisture or harsh temperatures (Belnap et al, 2001). Carbon (C) and nitrogen (N) fixation are two such functions. Photosynthesizing crust organisms facilitate the addition of both organic matter and inorganic carbonates to soils and can increase total soil C by as much as 300 percent (Pointing and Belnap, 2012). Cyanobacteria and lichens fix substantial amounts of N within crusts, increasing soil N levels and providing the nutrient to other microbes and plants that colonize the area. Soils crusts are also critical in promoting soil stabilization and limiting wind and water erosion. Reduced erosion can be important in terms of reducing dust deposition on snowpack within the Colorado River watershed, a process that is decreasing snow albedo and changing the timing of snowmelt. However, crust disturbance by grazing, trampling by hikers, vehicle traffic can reduce functionality of crusts and often cause even more severe erosion. Therefore, better management and regulation of traffic in areas with biological soil crusts is key to preserving their crucial roles in desert ecosystems. Increased monitoring and designation of high- and low- resiliency areas, considering factors such as species composition, soil stability, and water availability, may be key to improving management of crusts in sensitive areas.