Vegetation succession dynamics at the Alpine timber-line ecotone in the Grindelwald region (Northern Swiss Alps)

Abstract

This Ph. D. study investigates the importance of vegetation mappings (as proposed by Braun-Blanquet, 1964), in differentiating the type of dynamics of vegetation succession (non-disturbed/naturally determined vs. disturbed/anthropo-zoogenically determined) taking place in a newly forested surface at the Alpine timber line in the Grindelwald region. Non-disturbed and disturbed areas differ in their vegetation structure and phyto-diversity, as proved by previous studies. In this study we test these statements at the timber-line ecotone, which is an ecologically sensitive area and therefore well-suited for investigating changes in vegetation development, caused by non-disturbed (e.g., site conditions with intact ecological balance) and disturbed (e.g., site conditions with disturbed ecological balance) processes. For this purpose, we have chosen a site located in the region of Grindelwald that has shown the largest increases in forest cover at the timber line over the past 100 years. Our results show that phyto-diversity is more meaningful than plant structure when determining a surface area of progressing forest vegetation at the timber-line ecotone by its non-disturbed character, in probable response to global warming. We find a tendency for large parts of the current timber line to be anthropo-zoogenically determined, whereas non-disturbed/naturally shaped current timber line is limited to some local areas, as known from other Alpine regions. However, in the majority of studied areas the cause of current vegetation succession at the timber-line ecotone is unclear, neither attributable to the impact of possible global warming nor pasture reduction. These results reinforce the observations of previous studies that the timber line is unlike the snow line suited to showing the effects of evolutionary climate change as a global relation and that the spatial pattern of vegetation at the Alpine timber line is expected to behave non-synchronously with ongoing global climate change in the coming century.