Role of biological soil crusts in desert hydrology and geomorphology: Implications for military training operations

Abstract

Biological soil crusts, composed of soil surfaces stabilized by a consortium of cyanobacteria, algae, fungi, lichens, and/or bryophytes, are common in most deserts and perform functions of primary productivity, nitrogen fi xation, nutrient cycling, water redistribution, and soil stabilization. The crusts are highly susceptible to disturbance. The degree of perturbation is governed, at least in part, by the nature, intensity, and spatial and temporal distribution of the disturbance, as well as the soil type and soil moisture content at the time of disturbance. When disturbed, biological soil crusts lose their capacity to perform their ecological functions. Natural recovery of disturbed crusts can range from several years to millennia. Several strategies have been attempted to accelerate recovery of crusts. At present, artifi cial recovery is not economically feasible on large tracts of disturbed desert landscape. Management options available to the military on arid landscapes include: (1) eliminating or minimizing training in desert ecosystems, (2) avoiding critical seasons, (3) avoiding critical areas, (4) artifi cially restoring damaged crusts, and (5) considering desert training lands as “sacrifi ce areas.” Given the need to train in environments representative of the locations of many current and projected world confl icts, the fi rst option is untenable. At this time, the most plausible alternative is to consider desert training lands as “sacrifi ce areas.” However, it is recommended that attempts be made to avoid critical seasons and areas inasmuch as logistically feasible, and that the military continue to support research into the development of cost-effective technologies for biological soil crust restoration. Warren, S.D., 2014, Role of biological soil crusts in desert hydrology and geomorphology: Implications for military training operations, in Harmon, R.S., Baker, S.E., and McDonald, E.V., eds., Military Geosciences in the Twenty-First Century: Geological Society of America Reviews in Engineering Geology, v. XXII, p. 177–186, doi:10.1130/2014.4122(16). For permission to copy, contact editing@geosociety.org. © 2014 The Geological Society of America. All rights reserved. INTRODUCTION Biological soil crusts are characteristic of most arid and semiarid landscapes. Alternatively referred to as cryptobiotic, cryptogamic, microbiotic, microfl oral, microphytic, and organogenic soil crusts, they are formed when cyanobacteria, algae, fungi, lichens, and/or bryophytes colonize and inhabit the surface layer of arid soils. Filamentous cyanobacteria, algae, and fungi, as well as rooting structures of lichens and bryophytes physically entwine soil particles, creating a stable matrix. The crust is further consolidated by glue-like polysaccharide secretions of cyanobacteria, algae, and fungi. Biological soil crusts generally range from 2 mm to 2 cm in thickness, and perform a variety of essential ecological functions. Biological soil crusts have been reported from virtually every desert in the world (Belnap and Lange, 2001). At least