The manifestation of drought events in tree rings of beech and oak in northern Bavaria (Germany)

Abstract

The frequency and intensity of climatic extreme events is expected to increase in the near future in central Europe as a consequence of climate change (Schar et al. 2004). For northern Bavaria, an increase of summer temperatures of up to 2.4°C is expected, while summer precipitations are predicted to decrease (Rennenberg et al. 2004). Some climatic events manifest themselves by characteristic features such as frost rings, light rings, false rings or reaction wood. Droughts or severe storms are expressed by abrupt growth reductions which might alter growth for a number of years (Schweingruber 2001). Drought events might alter the intrinsic water use efficiency of trees and document themselves in variations of stable isotopes in wood cellulose (Bonn 2000, Skomarova et al. 2006). We present first results of a project (“FORKAST”) studying the effects of extreme drought events on trees of edaphically dry sites in northern Bavaria (Germany) during the last century. Special emphasis is laid on the resilience time needed by different tree species for recovering from extreme drought. We investigate a spatial network of chronologies of common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Mattuschka) Liebl.) by applying a multi-parameter approach including quantitative analyses of intra-annual variations of wood anatomy, wood density and carbon isotopes. The final goal of this study is to assess the adaptability of these tree species if frequency and intensity of drought events will increase in the near future. This will lay a dendroecological basis for forest management actions that may have to be taken in order to modify the forest structure on drought-prone sites as an adaptation to future climate change.