Die verbreitung und entwicklung der Grünerlenbestände in der ostschweiz

Abstract

In many subalpine regions of Switzerland, the Green Alder (Alnus viridis) is expanding as summer pastures are abandoned. The Federal Office for the Environment has set up a research project to improve the understanding of the characteristics of Green Alder and the consequences of its expansion. This project is based on a literature search, interviews with experts and GIS-based analysis of the past and present occurrence of Green Alder in three areas of eastern Switzerland. The results show that Green Alder is present at all exposures in the research areas. It is not lime-intolerant, but is less present on well drained basic subsoils. It is much more widespread than hitherto believed. In the canton of Glarus as well as in the Surselva, the area of Green Alder stands has doubled in the past 75 years. Only a few have developed to high forest stands. Therefore Green Alder stands should be considered, at least in their optimum oceanic sites, as permanent association, and not pioneer forests. In many places a broad belt of Green Alder has developed at the upper treeline, which is preventing the establishment of other species (e.g. Spruce) which might be possible because of climate change. Without intervention, the Green Alder stands will in all likelihood continue to expand over the coming decades. The areas affected by this expansion should be identified as of now, and a decision taken as to whether or not to tolerate this expansion. It is important that planning measures (agriculture, forestry, regional development) be taken early enough.