Spatial and temporal scale-dependent feedbacks govern dynamics of biocrusts in drylands

Abstract

Biota could be ecosystem engineers in generating an intrinsic heterogeneous landscape through scale-dependent feedbacks. Thereby, they can form resource enriched patchiness or islands of fertility, comprising of self-organizing spatial patterns. Research so far has largely focused on the self-organized spatial patterns of plant communities in drylands. It, however, remains unclear whether and how biocrusts having distinct morphology and life history from plant communities could self-organize themselves and form unique spatial patterns. Here we conducted field observations of biocrusts across successional stages and employed a probabilistic Cellular Automaton (CA) model to investigate the distinct self-organized spatial patterns exhibited by mosaic patches of mosses and lichens with different patch size distributions (PSDs). Our study demonstrates that short-range positive feedbacks initially promote the development of patches, featured with a heavy-tailed PSD, while long-range negative feedbacks subsequently curtail further expansion of big patches, thereby establishing a characteristic patch scale with regular PSDs. Strikingly, only lichens reverted back to the heavy-tailed PSD in the late succession stage, presumably implying self-organized critical fragmentation of lichen patches. Field measurements of biocrust performance at the center and edge of patches of varying sizes along succession stages further support the classic scale-dependent feedback mechanism for Turing pattern formation. Collectively, our results clearly demonstrate the capability of the biocrust communities to self-organize themselves to form distinct spatial patterns governed by the spatial and temporal scale-dependent feedbacks, potentially impacting dryland ecosystem functions and resilience. Significance StatementAn intriguing phenomenon is the capability of biota to form striking self-organized spatial patterns. Biocrusts serve as the soils skin and have different morphology and life history as compared to plant communities. We investigated these distinct self-organized spatial patterns exhibited by mosaic patches of mosses and lichens across succession stages through field surveys and a probabilistic Cellular Automaton (CA) model. Our results provide empirical evidence that biocrusts act as ecosystem engineers, forming self-organized spatial patterns. Simulations and field measurements of biocrust performance elucidate the mechanism of spatial and temporal scale-dependent feedbacks in governing biocrust spatial pattern formation. This self-organizing ability of biocrusts holds significant implications for ecosystem functions and the resilience of dryland ecosystems.