Ecological resilience after fire: the forest fire area above Leuk as a model case study.

摘要

The forest fire area above Leuk (Canton Valais, Switzerland) has served since 2004 for several studies on ecological resilience. On the 300 ha patch that ranges from 800 to 2100 m a.s.l., several samples have been installed. Vegetation changes were monitored representatively on a grid of 125 m cell size. The vegetation of the intact forest vegetation could be compared on a formerly assessed stratified sample and by re-assessing the actual vegetation. Along six horizontal transects at different altitudes, soil samples were taken from different layers of 25 soil profiles. Invertebrate fauna was collected weekly during the summer season at 18 localities along three transects at different altitudes. Localities were grouped into the three types "intact forest", "burnt forest" and "transition zone". One year after the fire, following results are at hand: For a wide area, the vegetation was literally missing. Surprisingly, at scales of 0.25 ha, the actual number of plant species was not significantly different from the former intact forest vegetation. As an indicator of fire intensity, the ash layer was significantly and negatively correlated with the vegetation cover in 2004. At altitudes between 1200 and 1600 m a.s.l., the fire intensity turned out to have been most severe. The fire resulted in a general increase of the pH in the top soil by means of 1 to 1.5 units if compared to unburned top soils of the corresponding communities, basically as an effect of burnt organic acids and by the loss of protons. A superficial hydrophobic carbonate layer resulted from cations freed by the burning process. In consequence, erosion processes on steep places were intensified. Invertebrate diversity was surprisingly high one year after the forest fire. The most frequent groups were beetles, aculeate Hymenoptera, two-winged flies, and parasitic wasps. About 50% of the collected individuals were pollinators and 28,5% were predators. Highest individual numbers were counted in the transition zone. The started projects will be continued in the next few years..