Effects of competition reduction on intra-annual radial growth of European beech (Fagus sylvatica L.) at stem base and crown base

Abstract

Key message: In beech stands, thinning affects growth differently along tree stems, with higher and longer duration increment at stem base than at crown base while unmanaged stands depict opposite patterns. Abstract: Forest management affects individual tree growth dynamics at different levels of the tree bole. Here, we assessed stem-growth patterns as a function of bole height (stem base and crown base) and competition reduction using high-resolution dendrometer records. We measured radial increments throughout the vegetation periods of 2015 and 2016 in two differently managed European beech (Fagus sylvatica L.) stands in central Germany. In one stand, trees had been repeatedly released from competition while the other had remained unmanaged for about 40 years. To assess different temporal phases of diameter increment, we fitted Weibull growth curves to dendrometer data. Stem basal area and crown base area increments of trees in the managed stand were always higher than in the unmanaged stand. In the managed stand, crown base and stem base monthly diameter increments were highly correlated until July when diameter increment at stem base surpassed the diameter increment at crown base. Conversely, in the unmanaged stand, monthly diameter increment at the stem base was often lower than at crown base. In both stands, diameter growth started earlier at crown base than at stem base. However, stem base growth in the managed stand began earlier and lasted longer than in the unmanaged stand. Our results confirm that competition reduction affects diameter increment along the stem differently than in unmanaged stands and increases growth duration. Future research is needed to test whether different growth patterns and tapers of residual trees in managed and unmanaged stands have implications for biomass and carbon storage modeling.