Extensive reductions of reindeer lichen heaths - repeated freeze-thaw cycles and ground-icing as potential key factors

Climate scenarios predict that high latitudes will experience a substantial increase in winter temperatures during the next decades. It has been suggested that repeated freeze-thaw cycles and the formation of ground-ice, which are induced by winter warmin g, will have profound effects on vegetation at high latitudes. There are indications that these phenomena can lead to extensive die-back of lichen heaths and other vegetation types in northern Fennoscandia. However data from field experiments are currentl y lacking. The combination of ground ice-crusts and reduced quality of the underlying vegetation can lead to far-ranging implications for reindeer herding in these areas. Instead of waiting for chance events to understand the importance of freeze-thaw cyc les and ground-icing, we need to gain predictive power through manipulative experiments. This will be done here by establishing permanent field plots for simulating winter warming and rain-on-ice events, and also by monitoring natural vegetation at differ ent altitudes, including sites with low and high reindeer trampling activity. By means of these approaches we (postdoctoral candidate and partners) will accomplish results that will answer the following fundamental questions: -Can increased frequency of f reeze-thaw cycles and ground-icing induce short-term and longer-term changes in vegetation composition? -If so, which changes take place; said in other words, which species and functional groups become more abundant, which species and functional groups ex perience a decline in abundance, and do new species establish? -Is the metabolic and ecophysiological activity of cryptogams affected by the increased frequency of freeze-thaw cycles and ground-icing? -Is it likely that freeze-thaw cycles and ice encaseme nt have contributed to the last decades' extensive and well-documented reduction of lichen-dominated heaths? -Will northern Fennoscandian reindeer pastures suffer from winter warming in forthcoming decades?