The relative contribution of grazing and climate variation on vegetation change in alpine area

Abstract

For more than a decade, a warming and grazing experiment has been carried out in the alpine area of the Faroe Islands. Ten Open Top Chambers (OTCs) were placed inside an enclosure with control plots both inside (CtrlE) and outside (CtrlO) the enclosure. The difference in vegetative growth of the two species Salix herbacea and Polygonum viviparum and graminoids were monitored as well as the frequencies of the four functional types: herbs, graminoids, woody species and bryophytes. It was found that warming generally increased leaf length by around 30% with similar or larger increases in photosynthetic leaf area. Grazing reduced leaf length by around 30% for graminoids and Polygonum viviparum, but only by around 10-20% for Salix herbacea. The changes in frequencies of functional types were most pronounced for bryophytes and woody species during the latter part of the experiment when both grazing-exclusion and warming increased the frequencies of bryophytes and decreased the frequencies of woody species.