Paradoxical role of the spatial heterogeneity in the functioning of drylands

Erosive soil processes in arid ecosystems render local heterogeneities and associated ecological and hydrological diversities within the landscape. Spatial heterogeneity exhibits simultaneous opposing degrading and developing conditions with varying degrees of resilience. While it would have been expected that heterogeneity-induced response diversity should increase the ecosystem resilience, highly heterogeneous ecosystems promote irreversible shifts. The major question is whether heterogeneity accelerates dryland degradation or provides an opportunity for increasing sustainability. To understand this paradox, recent studies were reviewed to answer (۱) the causes of spatial heterogeneity in patterns of soil biotic-abiotic properties; (۲) how heterogeneity simultaneously exhibits seemingly opposite effects in dryland dynamics through the emergence of resilience thresholds. Until heterogeneity can retain multiple resilience thresholds, it will have facilitative effects on resilience of the landscape. When the distance between fragments exceeds a dispersal threshold, the disappearance of resilience thresholds promotes destructive effects of the heterogeneity, stimulating irreversible transitions. It is hoped that this review, in emphasizing the importance of the relationship between erosive soil disturbances and soil biotic-abiotic variables in the dynamics of spatial heterogeneity can provide an effective basis to quantify critical heterogeneity thresholds as an early warning sign for anticipating the future evolution trend of landscape.

Keywords:

Dispersal scale , dryland , Pedoheterogeneity , Resilience , Soilscape