Debris flow; Dendrogeomorphology; Tree sensitivity; Ageing; Growth disturbance; Intensity reaction

Dating of geomorphic events using dendrogeomorphic methods has increased rapidly during the last years to provide a systematic overview on event frequencies, spatial reach and magnitudes. Despite the recent advances in methodology, multiple questions remain when it comes to the age-dependent sensitivity of trees which may further influence the quality of dating. Yet, the impacts of ageing effects on dendrogeomorphic reconstructions have not been assessed in detail so far. This study clearly shows the evolution of numbers, types, and intensities of growth disturbances (GDs) across the lifespan of three different tree species (Larix decidua Mill., Picea abies (L.) Karst., and Pinus sylvestris L.) affected by debris flows in the European Alps. Based on the re-analyses of datasets from past dendrogeomorphic reconstructions and calculation of statistical tests we investigated decreased ability of all studied tree species to record the debris-flow impact with increasing age.