Effects of grazing abandonment on soil multifunctionality: The role of plant functional traits

Extensive livestock grazing is a global land use activity that has numerous social, cultural, and environmental benefits. Many marginal zones grazed for centuries are now suffering from abandonment, which has been found to be interrelated with species and functional diversity loss, and has potential consequences for the provision of ecosystem services such as soil fertility and soil carbon storage. We sampled soil and plant species abundance in a total of 64 plots (5 x 5 m), in wet and dry habitats under different grazing regimes (from moderate grazing to grazing abandonment for at least 30 years) in Central Spain. We tested the influence of grazing intensity and water availability on different variables related to soil fertility and also on soil carbon storage. In addition, Community weighted mean and Rao quadratic entropy were calculated for two effect traits (specific leaf area and plant height), in order to assess the ultimate effects of these functional attributes on multifunctionality (i.e., the provision of several simultaneous ecosystem functions). We found that grazing abandonment generally produces a reduction in soil organic matter, total nitrogen, available potassium and phosphorus, aggregate stability and soil carbon storage. In addition, grazing abandonment had a negative effect on soil texture with loss of fine particles (clay and silt) and water holding capacity, but only in dry habitats and in longer-term abandoned situation. In general, soil multifunctionality was higher in wet than dry habitats, decreased with grazing abandonment in both habitats. Soil multifunctionality was indirectly mediated by the functional structure of size and leaf traits of the local plant communities, but our results suggested that macroscale grazing effects, i.e. translocation of nutrients by grazers among habitats via dung and urine deposition, might be important mechanisms that influence soil multifunctionality at the local level. Agri-environmental policies should be aware of the risk of widespread grazing abandonment and take advantage of the benefits of low-intensity grazing regimes for ecosystem services such as soil fertility and stability, and soil carbon storage.