Spatial pattern of tree species in an old-growth temperate forest: Chance or competition?

Background/Question/Methods Analyzing spatial patterns of tree speices can provide many important clues about the underlying processes that have generated these patterns. A 25-ha broad-leaved Korean pine (Pinus koraiensis) mixed forest plot was established on Changbai Mountain, P.R. China, in 2004 in order to gain insights into the processes driving regeneration and succession of the forest. All trees at least 1 cm in diameter at breast height were mapped and identified to species. In this study, the spatial distribution patterns and spatial associations of main tree species, density-dependent effects on tree survival, and the patterns of species co-occurrence were analyzed to evaluate the roles of chance and competition in structuring the community. Results/Conclusions We found that: (1) Intra- and interspecies spatial associations of varied with species, tree height, and scales. (2) Scale is an important factor for pattern formation, and different species showed different distribution patterns and spatial associations at different scales. (3) The analysis of density dependence on tree survival showed that, for common species, 3 of 5 canopy species and 3 of 8 midstory and understory species were random in mortality. Negative density-dependent mortality was not found when trees reach 1 cm in DBH. There was no significant correlation for canopy species between tree survival and conspecific abundance, but largely positive correlations for midstory and understory species. In contrast, tree survival was found to negatively correlate with conspecific basal area for most species. (4) The analysis of species co-occurrence pattern was conducted for all species, species with larger abundances, species with larger sizes, and five phylogenetic-based species groups at seven fine scales, and our results showed that competition is an important assembly rule at small scales in governing tree communities of our temperate forest, although it is not the only process involved. The importance of other processes should also be taken into account to explain spatial patterns of tree species.