Alpine plants in a warming world – particularly threatened or well buffered?

Stefan Dullinger

Due to steep climatic gradients, higher-than-average warming rates as well as conic shapes and limited elevation of mountains alpine plants have long been considered as particularly threatened by a warming climate. While niche-based modelling corroborates this expectation, empirical data have not provided clear evidence of such a particular risk far. In fact, colonization of high-mountain sites by newcomers has been the predominant trend over the last decades, while extinctions of resident species have been rare. Long extinction lag times and the buffering effect of pronounced microclimatic variation are alternative explanations of the unexpected trends. Here, I present results from recent research in my group which suggests, (1) that extinction rates are on the rise and lag times hence seem to be important; (2) the superior role of microclimate vs. macroclimate in driving alpine vegetation change cannot be demonstrated with the data available so far; (3) the maintenance of cold sites, as a result of microclimatic variation, does not automatically make them functional as refugia for cold-adapted plants due to strong dispersal limitation and frequently adverse non-climatic habitat conditions of exceptionally cold sites. I conclude that the climatic threats to alpine plants are considerable despite strong microclimatic variation in high-mountain terrain. I underline this conclusion by results of demographic modelling which suggest widespread negative population growth rates of alpine plants already under the climatic conditions of the most recent past.