Zehn Jahre Vegetationsdynamik auf der Waldbrandfläche von Leuk (Wallis)

Abstract

Ten years of vegetation dynamics in a forest fire patch in Leuk (Valais) The stand-replacing forest fire of Leuk (2003) extends from 900 to 2100 m a.s.l. and covers an area of 300 ha, which represents a big disturbance event in Switzerland, although it is small in a global perspective. Its location along a wide elevational gradient has offered a unique opportunity to study the dynamics of plant species richness and natural tree regeneration in relation to different environmental drivers. The vegetation was assessed on a systematic grid including 148 relevé plots and 5 time steps. Results show a peak of species richness in the fourth year after the disturbance and a distinctly higher number of species compared to the pre-fire forests. The increase of species richness during the first four years was slower on plots with highest fire severity. Above 1600 m a.s.l. species richness rose quickly above average due to the appearance of various mountain species. Tree regeneration has advanced in all studied elevation belts. Ten years after the disturbance, sapling densities ≥25 cm reached a rather low level of 1800 to 3000 stems per hectare. Aspen (Populus tremula), willow (Salix appendiculata and S. caprea), as well as birch (Betula pendula) are most abundant up to 1700 m a.s.l., where up to 95% of the regeneration consists of broadleaves. Above, European larch (Larix decidua) and Norway spruce (Picea abies) each constitute 12% of the regenerating saplings. At lowest elevations, oaks (Quercus pubescens) have established more frequently (6.4%) after ten years than Scots pine (Pinus sylvestris; 3.7%), even though the proportion of these formerly stand-forming tree species is still quite modest compared to the total number of stems per ha. Looking ahead, a young forest will grow on the forest fire patch, developing towards a larch-spruce forest at high elevations and towards a mixed forest with a considerable proportion of oak at low elevations. It may take quite a while until prevailing aspen, willow and birch will be overgrown by conifers and oaks.