The influence of climate, soil physicochemical properties and tree size inequality on tree slenderness in mixed forests of Northeastern China

Abstract

The tree slenderness coefficient (TSC) reflects tree stability and plays an important role in the development of near-natural silviculture programs and forest management decisions. However, there is a lack of TSC models to explore the factors that promote tree stability in mixed forests. Based on the data from 316 boreal and temperate mixed forest plots in northeastern China, this study developed a nonlinear mixed-effects TSC model for 14 tree species. Biotic and abiotic factors including climate, soil, wind speed, species mixtures, and diversity indices were tested for their regulatory effects on the TSC. Response patterns of each species' stability to changes in environmental factor gradients were simulated. In addition, this paper quantified the influence of biotic and abiotic factors on tree stability using the hierarchical partitioning approach. The results showed that mean annual temperature (MAT), mean annual precipitation (MAP), soil cation exchange capacity (CEC), the proportion of sand particles (SAND), mean wind speed (MWS), basal area proportions of the species of interest (BAP), and the Gini coefficient (GC) significantly influenced TSC. Tree stability increased with increasing MAT, CEC, and SAND. In contrast, increasing MAP, MWS, BAP, and GC negatively affected tree stability. The effects of biotic and abiotic factors on TSC were related to species heterogeneity. Our study quantified the drivers of tree stability in mixed forests and revealed the response patterns of TSC to environmental gradients, which will support further assessments of the stability of multi-species mixed forests under future environmental changes.