Livestock grazing abandonment reduces soil microbial activity and carbon in a Mediterranean Dehesa

Extensive livestock grazing is a major determinant of local biodiversity and ecosystem functioning in many regio1ns of the world. In sub-humid Mediterranean areas with long history of extensive grazing, abandonment of grazing has been linked to changes in the composition and structure of vegetation communities and decreases in soil multifunctionality, with potential cascading consequences for ecosystem services such as soil fertility and potential for soil carbon storage. Herein, we assessed the effects of livestock grazing abandonment on soil fertility and the ability of soil microbial communities to process organic matter (enzymatic activity and decomposition rate using the Tea Bag Index) in twenty-four study sites in a Quercus ilex dehesa from Central Spain. Sites were distributed across four levels of grazing (none, very low, low and moderate) and two levels of resource availability in terms of water and nutrients (upper slope and lower slope zones). Grazing abandonment and upper slope zones were associated with a lower accumulation of organic matter and availability of nutrients such as phosphorus and potassium in the soil. Grazing abandonment also had a negative effect on microbial enzyme activity, which was directly related to litter decomposition and the ability of microbial communities to stabilize soil carbon. Microbial effects were particularly marked in the lower zones, indicating the modulating role of topography on the consequences of land use changes. Environmental management policies should consider the positive ecological effects of traditional grazing in regions with long evolutionary history of grazing by domestic livestock, and how the abandonment of these practices could negatively affect soil ecosystem functions and the provision of soil-related ecosystem services.