Increase in soil aggregate stability along a Mediterranean successional gradient in severely eroded gully bed ecosystems: combined effects of soil, root traits and plant community characteristics

Our objectives were to evaluate changes in soil aggregate stability along a successional gradient, located in severely eroded Mediterranean gully bed ecosystems and to identify predictors of soil aggregate stability variations among several soil, root traits and plant community characteristics. We selected 75 plots in gully beds, representing five successional stages that differ in plant community composition, dominated by herbs, shrubs or trees according to successional stage. In each plot, we measured soil aggregate stability, basic soil characteristics, root traits and plant diversity indices. Soil aggregate stability increased along the successional gradient, being thrice higher in tree-dominated communities as compared to grass-dominated communities. This increase was mainly driven by soil organic carbon (SOC) accumulation. In early successional stages showing low SOC (below 24 g.kg(-1) or 12 g.kg(-1) in some cases), fine sand content and the percentage of fine roots acted as co-drivers enhancing soil aggregate stability while silt content decreased it. Plant succession in severely eroded Mediterranean gully bed ecosystems is accompanied by a strong stabilization of soil aggregates, mainly driven by SOC accumulation and for early successional stages, by soil granulometry and root traits as co-drivers. Stimulating succession thus appears as a promising restoration strategy for severely eroded ecosystems.