Long-term changes in biological soil crust cover and composition

Eva Dettweiler-Robinson,Jeanne M Ponzetti,Jonathan D Bakker

doi:10.1186/2192-1709-2-5

Eva Dettweiler-Robinson, Jeanne M Ponzetti + Show 1 more

Open Access

https://doi.org/10.1186/2192-1709-2-5

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Abstract

Communities change over time due to disturbances, variations in climate, and species invasions. Biological soil crust communities are important because they contribute to erosion control and nutrient cycling. Crust types may respond differently to changes in environmental conditions: single-celled organisms and bryophytes quickly recover after a disturbance, while lichens are slow growing and dominate favorable sites. Community change in crusts has seldom been assessed using repeated measures. For this study, we hypothesized that changes in crust composition were related to disturbance, topographic position, and invasive vegetation. We monitored permanent plots in the Columbia Basin in 1999 and 2010 and compared changes in crust composition, cover, richness, and turnover with predictor variables of herbivore exclosure, elevation, heat load index, time since fire, presence of an invasive grass, and change in cover of the invasive grass. Bryophytes were cosmopolitan with high cover. Dominant lichens did not change dramatically. Indicator taxa differed by monitoring year. Bryophyte and total crust cover declined, and there was lower turnover outside of herbivore exclosures. Lichen cover did not change significantly. Plots that burned recently had high turnover. Increase in taxon richness was correlated with presence of an invasive grass in 1999. Change in cover of the invasive grass was positively related to proportional loss and negatively related to gain. Composition and turnover metrics differed significantly over 11 years, though cover was more stable between years. This study can be a baseline for assessing change in crust composition due to anthropogenic influences.

Highlights

Communities change over time due to disturbances, variations in climate, and species invasions
This study can be a baseline for assessing change in crust composition due to anthropogenic influences
We examined the relationship between these variables and potential abiotic and biotic explanatory factors including exclosure from large herbivores, elevation, heat load index (HLI), time since fire (TSF), initial presence of B. tectorum, and change in B. tectorum cover

Summary

Introduction

Communities change over time due to disturbances, variations in climate, and species invasions. Sites with higher resource availability, such as moist microsites, can support more species (Garcia-Pichel and Belnap 2001) and can have higher productivity and more stability (Hooper et al 2005) Invasive species such as the annual grass Bromus tectorum can decrease crust cover and species richness (Belnap et al 2006). This grass may prevent crust from recovering (Dettweiler-Robinson et al 2013) by competing for resources and/or reducing the fire return interval (Brooks et al 2004). Succession may proceed differently based on timing and severity of disturbance, what portion of the community survived the disturbance, and the spatial arrangement of disturbed and undisturbed patches (White and Jentsch 2001)

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