Aerobiology and passive restoration of biological soil crusts

Abstract. Biological soil crusts (BSCs) commonly occupy the surface of many arid and semiarid soils, and disturbed soils in more mesic environments. BSCs perform many essential ecological services. Substantial resources have been invested trying to restore BSCs that have been damaged by anthropogenic disturbances, largely to no avail. The nexus of science related to crust restoration and to aerobiology strongly suggests that crusts can become reestablished via naturally occurring processes. Propagules of BSC organisms are found naturally in the atmosphere, and are transported long distances. Whether restoration occurs naturally in this way, or by costly attempts to produce and disseminate artificial inoculants, success is ultimately moderated and governed by the timing and frequency of adequate precipitation relative to the arrival of viable propagules on suitable substrate at an appropriate time of the year. For greatest ecological benefit, efforts should focus primarily on minimizing the scope and scale of anthropogenic disturbance of BSCs in arid ecosystems.