Components and Predictors of Biological Soil Crusts Vary at the Regional vs. Plant Community Scales

Lea A. Condon,David A. Pyke

doi:10.3389/fevo.2019.00449

Abstract

Although biological soil crusts (biocrusts) occur globally in arid and semi-arid environments, most of our knowledge of biocrust cover and ecology is from a relatively small number of locations worldwide. Some plant communities are known to have high cover of biocrusts, but the abundance of biocrusts is largely undocumented in most plant communities. Using a data driven approach, we identified 16 plant communities based on plant cover from the Assessment, Inventory, and Monitoring Strategy data from the Bureau of Land Management (AIM, 5200 plots). We found that abundance of lichens and mosses varies among communities, but that both components of biocrusts are present in all plant communities. Biocrusts are indicators of two of these communities: one that is defined by high cover of mosses and basin big sagebrush and one that is defined by high cover of lichens and shadscale saltbush. Using non-parametric multiplicative regression, we evaluated a suite of abiotic and disturbance variables to assess the degree to which climate and soils are associated with the abundance of lichens and mosses at the regional scale. At the regional scale, soil depth and maximum vapor pressure deficit were found to be strongly associated with the abundance of lichens and January minimum temperature dictated the abundance of mosses. At the scale of plant communities, community specific metrics of soil and climate were better able to explain the abundance of biocrusts. Given our demonstration of the presence of biocrusts across the western US, we hope to call attention to the need to include biocrusts in studies on ecosystem function given their arguably stronger association with climatic variation, direct association with soils, and their contribution to ecosystem functions that are not solely maintained by vascular plants.

Highlights

Interspaces among vascular plants in undisturbed semiarid ecosystems are occupied by biological soil crusts, referring to lichens, mosses, and cyanobacteria that grow on the soil surface (Belnap and Lange, 2001)
Lesser spikemoss and associates are common of alpine and meadow communities (Billings, 2000) and these species are common in the grasslands of the northwestern Great Plains of Montana, North Dakota, and South Dakota (Crane, 1990)
We demonstrate the presence of the lichen and moss components of biocrusts in all plant communities across the semi-arid western US, concluding that the absence of the lichen and moss components of biocrusts is not a result of their being unable to grow in the environmental setting in any of our identified plant communities

Summary

Introduction

Interspaces among vascular plants in undisturbed semiarid ecosystems are occupied by biological soil crusts (biocrusts), referring to lichens, mosses, and cyanobacteria that grow on the soil surface (Belnap and Lange, 2001). Many of these organisms contribute to nutrient and hydrologic cycling, dust capture, and all of them contribute to the prevention of soil erosion (Evans and Ehleringer, 1993; Belnap and Gillette, 1998; Reynolds et al, 2001; Barger et al, 2006; Bowker et al, 2011). Working across scales would allow for a demonstration of the degree to which biocrusts are specific to a particular plant community vs. the degree to which they may be ubiquitous across communities of the western US

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Discussion

Conclusion