Natürliche Baummortalität in Mitteleuropa: Mortalitätsraten und -muster im Vergleich

Mortality is one of the key processes of forest dynamics. Yet, its investigation is challenging since trees can reach high ages, and tree death is the result of several interacting drivers. Long-term monitoring data from unmanaged forests are of great importance for studying mortality. Such data from strict forest reserves in Switzerland and Germany were used in this study to 1) derive mortality rates for 18 wooden species, and 2) build species-specific mortality models. Estimated mortality rates were highly variable among the reserves, and were particularly high in stands with many young trees and a high share of short-living pioneer species. For the calculation of accurate and comparable mortality rates, adjustments towards the same caliper threshold and mortality period are necessary. Models that predict the mortality probability of individual trees can be built based on stem diameter and basal area growth. Such models revealed that small and slow growing trees had the highest mortality risk. In addition, mortality patterns featured species-specific differences. Short-living species experienced high overall mortality probability. Shade-intolerant species showed a more pronounced mortality risk at small diameter and slow growth than shade-tolerant species. Competition as well as drought and frost were identified as the dominant drivers of tree mortality in the Swiss and German reserves. Pronounced age-related mortality due to senescence was not present, in contrast to a primeval beech forest in Ukraine. In the reserves, mortality rates and patterns should become more and more similar to those of primeval forests; however, it will require several decades or centuries of undisturbed forest development to reach identical successional stage.