Small-scale spatial patterns of biological crusts in a Mediterranean semi-arid ecosystem

Biological crusts are a common feature of soil surface in and and semiarid ecosystems, where they play a major role in ecosystem functioning and dynamics. In recent years, there has been an increasing interest in the ecophysiology, taxonomy, and dynamics of these crusts, but little is known about the effect of vascular plants on their small-scale spatial distribution. With the aim to increase our understanding about the interactions between biological crusts and vegetation in semi-arid areas, in this paper I evaluate the spatial pattern and interaction of two biological crusts components, foliose lichens and mosses, at two microsites in semi-arid Stipa tenacissima L. steppes of SE Spain. The aim of this paper was to determine if the microsite provided by S. tenacissima tussocks promoted changes in the individual patterns and in the spatial covariation of these crustal components. I used spatial analysis by distance index (SADIE) to explore the individual patterns and the spatial relationships between them. SADIE detected a significant clumped pattern in the spatial distribution of both species, but the effect of S. tenacissima tussocks promoted changes in the spatial pattern only in the foliose lichens. I did not find any microsite effect on the spatial relationships between the foliose lichens and the mosses. The results showed that the microenvironment provided by S. tenacissima is able to modify the small-scale spatial pattern of foliose lichens in semi-arid steppes, and suggested the presence of facilitation between S. tenacissima and these lichens.