Phenological phases of common beech (Fagus sylvatica L.) and their dependence on region and altitude in Southern Germany

Abstract

Long-term observational data of the phenological network of the German Weather Service (DWD) were used to derive the altitudinal dependence of leaf unfolding (LU), leaf discolouration (LD) and the length of the vegetation period (LD-LU) of common beech (Fagus sylvatica L.) in different regions of Southern Germany. Depending on altitude, the vegetation period starts in Bavaria between the 2nd and 24th May with a delay of around 2 days per 100 m altitude increase (averaged over the last 30 years). In Southern Bavaria, LU starts a few days earlier as well as increases slightly faster into higher altitudes than in the northern regions. This can be explained by a more favourable supply of warmth and radiation in the south. The end of the vegetation period, defined here as the beginning of LD, showed no altitudinal dependence, which reflects an interaction of endogenous and exogenous factors as triggers for LD. In the Bavarian Forest region, altitudinal dependences are strongly influenced by sites which are affected by cold-air tailback (‘Kaltluftstau’) was obtained. Hence, phenological gradients should only be derived and applied above a phenological inversion zone. The calculated vertical gradients for LU can be used together with available observational data to estimate the beginning of the forest vegetation period of beech for different altitudes of Bavaria.