Spatial associations among major tree species in a cool-temperate forest community under heterogeneous topography and canopy conditions

Analysis of the spatial pattern of plants may provide insight into the processes and mechanisms that promote species coexistence and community organization. Using torus-translation tests and point-pattern analyses for a heterogeneous Poisson process, we investigated habitat association and intra- and inter-specific spatial relationships of six major tree species in a cool-temperate forest community. All stems ≥5 cm in diameter at breast height were mapped on a 1.4-ha (100 × 140 m) plot and the topographic conditions (convexity and slope degree) and canopy state were assessed. Our results showed that all six species exhibited habitat associations with topographic and/or canopy conditions except for Magnolia salicifolia. Intra-specific aggregation was found for Acer japonicum, M. salicifolia, and Hamamelis japonica var. obtusata. Community-wide analysis of the inter-specific spatial patterns showed mainly mixed or partially overlapped patterns at a scale of up to 30 m, whereas individual pairwise analyses of inter-specific patterns revealed that Fagus crenata was positively associated with two Acer species and M. salicifolia at a spatial scale of up to 5 m. These results highlight that scale-dependant ecologically important processes, such as species-specific habitat preference, regeneration mode, seed dispersal, facilitation and niche complementarity, may operate simultaneously to shape tree distributional patterns, although their presence/absence as well as relative importance vary among species. Given the complexity of the process and mechanisms promoting species coexistence and community organization, more attention should be given to the effect of spatial scale in analyzing the spatial patterns of tree species in forest communities.