Insights into ecosystem composition and function in a sequence of degraded semiarid steppes

We evaluated changes in ecosystem function in semiarid Stipa tenacissima L. steppes along a degradation gradient in southeast Spain. We used soil surface indicators to obtain surrogates of ecosystem function (resistance to erosion, infiltration, and nutrient cycling) and related these values to the main abiotic and biotic characteristics of the experimental sites. When ranked in an ordered sequence, the trajectory of these indicators showed abrupt changes, providing empirical evidence of discontinuities in ecosystem function along the degradation gradient evaluated. Surrogates of resistance to erosion showed nonlinear relationships with variables defining the spatial structure of patches, the area covered by sprouting shrubs, and species richness. The latter two variables were significantly related to surrogates of nutrient cycling and infiltration. Our results suggest that sprouting shrubs are playing a key role in improving ecosystem function and composition in degraded S. tenacissima steppes. The implications of our results for the optimization of restoration procedures in semiarid degraded steppes are discussed.