Effects of grazing exclusion on species composition in high-altitude grasslands of the Central Alps

Our study examines the effects of grazing exclusion on low-productive subalpine and alpine grasslands of the Central Alps (UNESCO Biosphere Park Gurgler Kamm, Obergurgl, Austria). A long-term exclusion experiment was established in 2000 in the subalpine, the lower, and the upper alpine zone. With exception of the subalpine zone, domestic herbivores have been grazing during the whole growing season. In grazed and exclosure plots species frequencies were recorded for 7 years. We analysed exclosure effects on species number, community composition, life forms, and functional groups. Species richness did not decrease significantly within the exclosures, but changes in species composition occurred in each zone, although some were transitory in nature. The dynamic trends of the plots were significantly explained by the 'treatment x year' effect along the whole altitudinal gradient, but the effects decreased considerably with altitude. In the subalpine and upper alpine exclosures, stress-tolerators, species or low or no nutritive value, and mosses showed a decreasing trend, whereas tall grasses (subalpine exclosures), competitors, and species with high or medium nutritive values (lower alpine exclosures) tended to increase. Overall, our 7-year study revealed that. several functional groups reacted to grazing, according to Our main expectations. We suggest that these effects will intensify in the long term. (C) 2008 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.