Biological soil crust rehabilitation in theory and practice: An underexploited opportunity

Biological soil crusts (BSCs) are ubiquitous lichen-bryophyte microbial communities, which are critical structural and functional components of many ecosystems. However, BSCs are rarely addressed in the restoration literature. The purposes of this review were to examine the ecological roles BSCs play in succession models, the backbone of restoration theory, and to discuss the practical aspects of rehabilitating BSCs to disturbed ecosystems. Most evidence indicates that BSCs facilitate succession to later seres, suggesting that assisted recovery of BSCs could speed up succession. Because BSCs are ecosystem engineers in high abiotic stress systems, loss of BSCs may be synonymous with crossing degradation thresholds. However, assisted recovery of BSCs may allow a transition from a degraded steady state to a more desired alternative steady state. In practice, BSC rehabilitation has three major components: (1) establishment of goals; (2) selection and implementation of rehabilitation techniques; and (3) monitoring. Statistical predictive modeling is a useful method for estimating the potential BSC condition of a rehabilitation site. Various rehabilitation techniques attempt to correct, in decreasing order of difficulty, active soil erosion (e.g., stabilization techniques), resource deficiencies (e.g., moisture and nutrient augmentation), or BSC propagule scarcity (e.g., inoculation). Success will probably be contingent on prior evaluation of site conditions and accurate identification of constraints to BSC reestablishment. Rehabilitation of BSCs is attainable and may be required in the recovery of some ecosystems. The strong influence that BSCs exert on ecosystems is an underexploited opportunity for restorationists to return disturbed ecosystems to a desirable trajectory.