Short-term effects on sheep pastureland due to grazing abandonment in a Western Mediterranean island ecosystem: A multidisciplinary approach

Changes of pasture communities consequent to management practices resulting from land abandon- ment considerably affect the structure and function of the ecosystem. This study analyses the consequences of grazing abandonment in terms of plant and soil microbial diversity and fertility, on a Mediterranean upland sheep pasture,over a short period(five years). Grazing was experimentally excluded by fencing ten 10x10 m permanent plots within an area that had supported grazing until 2000, by 0.23 sheep ha-1. Plant and soil microbial communities and physicochemical parameters were monitored within the fenced and unfenced control plots, during three sampling times from 2000 (before the fencing)to 2005. Grazing cessation notably altered the floral composition, with an average dissimilarity of 96.7%between the vegetation communities, over five years. No significant change occurred in the control plots that were grazed throughout the sampling period. This work highlighted that, over a short term, the structural change in the specific plant composition affected only the grass species, confirming that grazing favours the small-sized species over the annual species. Further, it was evident that species groups of conservational and phytogeographic interest, like the endemic and Mediterranean-Atlantic species, tended to disappear with pasture abandonment and were substituted by more widespread species throughout the Mediterranean or even the world. Pasture abandonment was accompanied by an increase of soil pH and a decrease in soil organic matter and soil nitrogen. The microbial parameters recorded at three different sampling times revealed a substantial effect of the plant community, or the time of grazing abandonment, on soil microbial abundance and diversity. Considerable importance is given to the consequences of pasture abandonment on the conservation of plant and microbial diversity and on soil fertility.