Impact of canopy disturbances on climate sensitivity of old-growth beech (Fagus sylvatica L.) forests

Abstract

Canopy disturbances can affect tree growth and mask climate signals in tree rings. Their magnitude and lasting effects, however, remain poorly understood, potentially obscuring dendroclimatic analyses in closed-canopy forests. Here, we evaluate the influence of canopy disturbances on the climate sensitivity in European beech (Fagus sylvatica L.) in three old-growth forests spanning a wide range of ecoclimatic conditions. Growth-release detection was used to identify disturbed and undisturbed trees and assess their sensitivity to maximum temperature, precipitation, vapor-pressure deficit, diurnal temperature range, and cloud cover over two periods (1902–2022, 1962–2022). Our results indicate that, across all sites, growth was primarily driven by moisture availability and previous-season maximum temperature. While growth releases cause short-term deviations at the individual-tree level, they have limited impact on the strength, timing, and stability of climate–growth relationships. Comparison of sites from northern Germany to southern Italy reveal a north-to-south narrowing of climate-sensitive growth periods and a notable increase in sensitivity during the late 20th century. Despite their short-term influences, our findings show that disturbances in old-growth beech forests act only as secondary modifiers rather than primary drivers of climate-growth relationships and thereby justify dendroclimatic reconstructions without prior disturbance adjustment.