The Valais is among the most extreme inner-Alpine dry regions.The distinct temperature increase of the recent years results in increasing drought stress for plants during dry years. In Valais forest vegetation is presently in change: mortality processes in Scots pine (Pinus sylvestris L.) go along with an increase of broadleaved trees, mostly downy oak (Quercus pubescens Willd.). A combined approach (assessment of forest structures on a regular grid, intensive monitoring and experimental plots, and analysis of past forest management) was applied to analyze the shift in tree-species composition and to keep apart the impact of changes in climate and land-use.
The shift from pine to oak was most pronounced on dry sites, where pine mortality was highest and oak regeneration most frequently. Pine mortality was highest after dry years, whereas oak was less affected. Although oak regeneration seems to profit from the dryer climate, the changes of the land-use regime during the past decades was identified as the main driver for the increased spread of oak.