Alpine vegetation under atmospheric change

Background/Question/Methods High elevation vegetation is commonly considered dominated by effects of low temperature with all other drivers of life such as carbon, water, and nutrient supply playing secondary roles. In this talk, this hierarchy will be questioned, given that temperatures are modified by vegetation and topography, offering a suite of quite contrasting temperature regimes over short distances. Another common claim is nutrient limitation, because of slow nutrient cycling, and carbon starvation, because of thin air, and thus, low partial pressure of CO2 at high altitude. Therefore, atmospheric nitrogen deposition and CO2 enrichment might be seen as a relief and benefit. Both these views will be challenged on the basis of limitation theory in an ecological context, and by in situ experimental data from the Swiss Alps. Results/Conclusions Large-scale infra-red thermometry conclusively confirms earlier point-data, that topography exerts greater effects on temperature in alpine vegetation than several hundred meters of elevation. Adding inorganic nitrogen compounds, affects plant species interaction and is likely to cause competitive exclusion, with a few vigorous species taking advantage. Hence, soluble nitrogen deposition is a biodiversity threat rather than a relief. Elevated CO2 has no stimulating effect on alpine plant growth (even some negative effects have been observed), presumably, because stomata-driven water savings (explaining most low elevation responses) are not relevant in a commonly wet and cold alpine environment. While there are rapid plot scale, species specific responses to experimental warming, overall species diversity will be much less affected by climatic warming in the alpine compared to the plains, because a rich micro-habitat diversity provides short distance escapes. We thus question the frequent claims of particular vulnerability of alpine biodiversity to climate warming. The most likely effect of higher temperatures is a local re-arrangement of alpine species abundance. Trees at treeline will profit, leading to a slow invasion into alpine terrain. Since natural plant communities are never nutrient limited (whereas productivity, irrespective of species, regularly is), any anthropogenic input of nutrients will affect biodiversity. Alpine vegetation is carbon saturated at current CO2 concentration. Land use change will exert impacts exeeding those by atmospheric change in many cases. References: Körner, Alpine Plant Life, Springer 2003;. Scherrer & Körner, Glob Change Biol 2010 in press.