Driving factors of the growth response of Fagus sylvatica L. to disturbances: A comprehensive study from Central-European old-growth forests

Abstract

Despite improvements of dendrochronological techniques in many forest ecosystems, studies describing the growth responses of trees following disturbance events including comprehensive data on factors and processes behind tree-growth release are rare, especially for European temperate forests, limiting the interpretation and generalization of dendroecological studies. Here we examine the effect of key factors on the growth reaction of Fagus sylvatica L. to disturbances in 8 old-growth forests in the Czech Republic, independently dated using three different data sources – tree censuses, dendrochronology and historical aerial photographs. Using 117 increment cores, we studied four parameters of radial tree-growth surrounding canopy gaps: magnitude, duration, abruptness and response shift, in relation to factors of different spatial scales, i.e. tree-, gap- and stand-level variables. Our results indicate that the beech growth response to gap formation strongly differs across a complex of factors at diverse spatial levels, frequently occurring in noteworthy interactions. A positive trend for the gap size * radiation interaction in the analysis of magnitude was found, suggesting that the effect of gap area differs among topographical features. As for duration and abruptness, the interaction of distance and mortality mode was identified, indicating a longer and more gradual reaction along with increasing distance of the cored tree from the gap centre, varying by the type of the gap maker’s death. In addition, an altitudinal gradient was found to predict the magnitude of growth changes and the time interval between the disturbance and the reaction of nearby trees. Surprisingly, the diameter of the surviving trees was not a good predictor of radial growth, with a significant positive relationship to just abruptness. An effect of locality was not observed, facilitating the broad applicability of our findings across a wide range of beech-dominated temperate forests. Our results emphasize the general limits of dendrochronological data in disturbance spatial pattern studies, as indicated by the considerable variability in the responses of neighbouring trees to identical disturbance event. A detailed examination of the growth reaction, considering not only the response magnitude but also other important parameters, plays a key role in the precision of detecting growth releases as well as in reducing the sample size required for summary disturbance history evaluations. In focusing on this issue we believe we contribute to future dendroecological research by demonstrating the need for more precise disturbance history evaluations.