Most natural disturbances to Swiss forests are caused by climatically induced extreme events: winter storms, foehn and thunderstorms predominate in the North of the Alps, and forest fires in the Southern Alps. Many studies predict a general increase of these extreme events under continued climatic change. How resistant are Swiss forests against wind and fire disturbance, and how resilient are they after disturbance? Because in Switzerland most of the severe winds happen in the wintertime, conifers such as Norway spruce and silver fir are the most vulnerable species. Beyond gust speeds of more than 40 m/s, all tree species are damaged. The fire resistance of forests depends on the flammability, which will increase due to increasing drought frequency. Forests in the Ticino will be most affected by this development, and to a lesser extent also forests in the Central Alps and those north of the Alps. After wind and fire disturbance, forest has re-established in almost all regions of Switzerland. Results from various studies in disturbed forests show that the amount of tree regeneration decreases with increasing elevation (R2 = 0.31). After fire, the speed of regeneration depends on various factors such as tree species, drought and the transient absence of mycorrhiza.
The natural regeneration process after severe forest disturbances reflects a first step towards a forest more adapted to the future. Trees that establish in big gaps and under repeated drought may resist the future climate.