Drivers of forest structure and biomass along a climatic gradient in the Soutpansberg, South Africa

Forest structure plays a key role for providing different ecosystem services in rural regions worldwide. In forests and woodlands of southern Africa, there is a lack of quantitative information on prevailing structures, their abiotic and biotic drivers, as well as how stand characteristics will be affected by climate change. In this study, we established permanent research plots in mature developing stages of representative forests and woodlands occurring along a strong climatic gradient. Effects of site-available soil water and forest type were investigated for relevant dendrometric, as well as structural forest variables. We found site-available soil water having a significantly positive effect on all variables, apart from tree density and the ratio of multi-stem trees. Among the factors influencing site-available soil water, climate had a higher impact than topographical wetness index and soil available water capacity. Studied variables were also strongly influenced by the different forest and woodland types emerging, probably due to different species compositions, survival strategies and fire adaptations. Structural forest variables were revealed to have a positive effect on AGB especially in taller stands having enough space to form multiple canopy layers. In light of climate change with less soil water available and a related ongoing species and biome shift in southern Africa, our findings indicate that in the future, most of the studied forest variables, their related ecosystem functions and services are likely to decrease in the Soutpansberg region. The results of this study could be of use as input data for landscape level modelling, as well as for creating local management policies.