Elevational advance of alpine plant communities is buffered by herbivory.

摘要

Question: A warming climate has been linked to changes in the distribution of many species, yet the interactions between climate and other environmental drivers are relatively poorly understood. Mountain regions are expected to be particularly at risk in a warming climate, and in many upland regions land use has also changed dramatically over the past few decades, with densities of grazing livestock often decreasing. Does livestock grazing influence elevational shifts of plant communities? Location: Southern Scandes, Norway. Methods: We use a unique long-term experimental study at the landscape scale along an altitudinal gradient to study elevational shifts of plant communities and species under high and low sheep densities and in ungrazed conditions. Results: We show that elevational advance of the whole alpine grassland plant community occurred in the absence of herbivores (with a 3 m elevational advance over 8 yr), but was suppressed at low sheep density. At high sheep density there was a downward shift in plant community composition of 4 m. The average change in median altitude across species was positive in the absence of herbivores, but not significantly different from zero under both grazing treatments. There was no convincing evidence that species from lower altitudes showed a greater elevational advance than species from higher altitudes. Conclusions: This study presents evidence that grazing sheep suppressed an elevational advance of the plant community, suggesting that grazing can limit the altitude of the plant community. This implies that grazing management has the potential to buffer climate-driven shifts in plant communities. Conversely, the widespread recent changes in land use, with reductions in large herbivore densities in alpine areas, could further increase the vulnerability of alpine communities to warming.Digital Object Identifier http://dx.doi.org/10.1111/j.1654-1103.2012.01391.x