Vegetation and soil seed bank in a 23-year grazing exclusion chronosequence in a Mediterranean dry grassland

Abstract

Long-term grazing shaped plant diversity in dry Mediterranean grasslands. Abandonment of grazing affects plant diversity especially in the northern Mediterranean. Considerable efforts are, therefore, under way for grassland conservation and restoration. Yet, we do not know at which temporal scales impacts of grazing abandonment appear and in particular how soil seed banks evolve after longer grazing abandonment. Here, we provide detailed data from one of the very few long-term experiments available. These experiments provide data for up to 23 years (1982–2005) of grazing exclusion built in 1982, 1989, 2000 and 2001. Grazing exclusion decreased species richness, modified vegetation structure and changed soil parameters. Decline in species richness appears in communities that experienced 16 and 23 years of grazing exclusion. Only four to nine plant species of this Mediterranean grassland built persistent soil seed banks appearing after grazing exclusion, compared to 40–50 species in the established vegetation of grazed plots. Hence, similarity between vegetation and soil seed bank decreased with time of grazing exclusion. Even 23 years after abandonment, no woody plants colonised the experiments. We conclude that vegetation will recover fast from grazing abandonment in the short-term. Nevertheless, longer abandonment will impact diversity due to reduced soil seed banks.

Keywords:

• Species richness
• herbivory
• disturbance
• sheep
• succession

Acknowledgements

We are grateful to the CEN PACA and Ecomusée de Crau and the Nature Reserve of the Coussouls de Crau for their authorisation to carry out soil samples and access to study sites.

Notes

1. Plinius, Naturalis Historia 21.57.