Master Thesis

Auswirkungen des Klimawandels auf Diversitätsmuster von Waldquellen nordostbayerischer Mittelgebirge

Mario Schanz (03/2022-09/2022)

Support: Carl Beierkuhnlein

The forest springs of the north-eastern Bavarian low mountain ranges are characterised by largely uniform hydrogeological conditions. They are seepage springs fed by an interflow, so that there is a close connection between spring water characteristics and factors of the catchment area. In addition, the springs are mostly located on slopes used for forestry, which is why they represent near-natural habitats with little anthropogenic influence. The species composition of the forest springs is mainly determined by the acidity of the spring water and the light supply. Pronounced summer droughts as a result of climate change have led to the drying up of some springs in recent years. The effects of these drying events on the diversity patterns of spring ecosystems are largely unknown and were therefore investigated in the present work. We hypothesised that intermittently dry springs would show differences in vegetation composition compared to permanently pouring springs, and that these differences would be smaller in the highly acidic springs. We expected higher dominance of liverworts compared to mosses in the continuously pouring springs than in the intermittently dry springs. We also hypothesised that spring water pH and light availability remain important environmental factors that can explain differences in species composition. To this end, in spring 2022 we took releves of 102 springs distributed evenly over the two north-eastern Bavarian low mountain ranges of Frankenwald and Fichtelgebirge, estimated their discharge and measured the pH value, conductivity and temperature of the spring water. An ordination of the spring sites with the method of Non-Metric Multidimensional Scaling (NMDS) shows that the intermittently dry springs cannot be distinguished from the continuously pouring springs by their species composition, even when analysing the springs with different degrees of acidification separately. Furthermore, the liverworts do not show higher dominance in the continuously pouring springs compared to the mosses. In contrast, we were able to confirm that the spring water pH value and the light availability continue to be important environmental factors influencing the species composition. The finding that the drying out of the forest springs in recent years has not caused any change in the current vegetation composition indicates that the spring ecosystem has so far been highly resistant to the effects of climate change. This is presumably favoured by the deepening of the forest springs into the surrounding terrain relief, because this maintains a cool, moist microclimate for longer. Given the widespread distribution of helocrene forest springs with similar environmental conditions in Europe, our results provide supra-regionally relevant insights into the impacts of climate change.