Effects of grazing exclusion and environmental conditions on the soil seed bank of a Mediterranean grazed oak wood pasture

Large seed banks in the soils of Mediterranean wood pastures can allow the composition of the understorey vegetation to adapt to changing conditions such as under-grazing, grazing exclusion and climate change. This three year study investigated the effect of grazing exclusion on the transient and persistent seed banks of 23 areas of a Mediterranean wood pasture of Quercus suber L., Q. ilex L. and Q. pubescens Willd. A canonical correspondence analysis was used to determine the effect of topo-climatic (elevation, aspect, slope, rainfall, temperature, tree coverage), soil (pH, soil texture, and soil nitrogen, phosphorus, lime and organic carbon content) and biodiversity (Shannon index, species richness index, and Pastoral Value) variables on the soil seed bank under grazed and ungrazed conditions. The size of the persistent seed bank increased with rainfall, grazing, and the available phosphorus content of the soil. Specific site by site grazing regimes could increase the abundance of legumes in the soil seed bank and the species richness and diversity of the understorey vegetation. These results can help guide the conservation management of this silvopastoral area.