Tree growth and resource allocation in forest stands: Empirical evidence substantiated by scenario simulations

The focus of this study is on the resource and growth distribution between trees in forest stands and the dependency of this distribution on site conditions. Growth distribution patterns of forests, empirically revealed and modeled on stand level, still lack of a causal explanation. Therefore, a physiological individual tree growth model was applied in order to explain recently published general growth distribution patterns. Our study focuses on Norway spruce (Picea abies (L.) H. KARST) and European beech (Fagus sylvatica L.). This way, simulation results of the physiologically based growth model were compared to empirically found principles of resource allocation. The results of the scenario analyses suggest that the degree of size-symmetry increases with the trees' limiting factors, light and water. Size-symmetric competition and growth was found on poor sites whilst size-asymmetric behavior is dominant on more fertile sites. Synergies made by combining empirical research and model based hypothesis testing are discussed. The study also reflects that the use of physiologically based growth models can contribute to a better understanding of stand dynamics. Consequently, biological causalities based on the analysis of model simulations can support empirical findings.