Sustainable forest management practices and the increased interest of plantation forestry in species mixtures require an understanding of individual-tree growth in complex and diverse forests. Individual-tree growth has been found to be affected by factors such as species identity and size of the target tree as well as of neighboring trees, neighbor density and abiotic factors. However, most of these studies have been conducted in plantations or mixed forests with a very limited number of species. We conducted our study in a subtropical forest in China, which was very species rich and highly heterogeneous with regard to topography (slope inclination and aspect, elevation) and successional status. Prior to our study the forest was subjected to an exceptional snow break event. We asked whether individual-tree basal area increment (BAI) over three growing seasons following the snow break event was related to local biotic and abiotic conditions. We hypothesized that individual-tree BAI is negatively affected by local neighborhood competition, positively affected by local neighborhood diversity, negatively related to slope inclination, and positively related to aspect to south. Individual-tree BAI of four different species was mainly affected by tree size, local neighborhood competition and species identity. Contrary to our expectations, we did not observe significant effects of local neighborhood functional diversity and abiotic conditions. However, we did find a negative effect of plot functional diversity on BAI. This finding may be explained by a negative correlation of plot functional diversity and snow break damage, which was observed in mid- and late-successional stages. The disturbance event did considerably change the competitive local neighborhood interactions by reducing competition, which increased the BAI of target trees in more disturbed/more diverse plots.

Keywords

Basal Area Increment, Crown Projection Area, Functional Diversity, Gutianshan National Nature Reserve, Local Neighborhood Diversity