The effect of tree size, neighborhood competition and environment on tree growth in an old-growth temperate forest

Aims Understanding the controls influencing tree growth is central to forest ecology. Although many factors such as tree size, neighborhood competition and environmental variables, have been proposed as being important in explaining patterns of tree growth, but their relative contributions are still subject to debate. We aimed to examine the relative importance of tree size, local abiotic conditions and the density and identity of neighbors on tree growth in an old-growth temperate forest in northeast China. Methods We used linear mixed models with data from a 25 ha (500 × 500 m) broad-leaved Korean pine (Pinus koraiensis) mixed forest permanent plot to examine the relative importance of these local drivers on tree growth at three organizational levels (community, guild and species). Subplot was included as a random effect to account for spatial autocorrelation in growth of trees located within the same subplot, and species was included as a random effect to account for variation among species in growth. Important Findings Tree size was typically the most important predictor of growth, followed by neighborhood competition and then soil nutrients. The correlation of tree size to growth varied from strongly positive for large trees and medium trees to slightly positive for small trees. The effect of neighborhood competition on growth showed weak negative density dependence as indicated by slightly negative effect of total basal area of neighbors and the proportion of conspecific neighbors. Environmental factors influenced growth of very common species, smaller tree-size classes and shade-tolerant species. We concluded that the relative importance of variables driving patterns of tree growth varied greatly among tree size classes, shade tolerance and abundance classes in this temperate forest. These results provide critical information for future studies of forest dynamics and offer insight into forest management in this region.