Spatial patterns and associations of six congeneric species in an old-growth temperate forest

Analyses of the spatial patterns of pairs of sympatric congeneric species present unique opportunities and challenges in explaining species coexistence. In this study, we compared the population structure and spatial patterns of six coexisting species of Acer (maple) in a large-scale 25-ha old-growth temperate forest plot in northern China with the aim of gaining insight into the coexistence of these congeners. A second-order spatial point pattern analysis based on the pair-correlation function was used to evaluate spatial patterns and examine intra- and interspecies associations among them. The abundance varied from 251 to 6609 individuals, but these species showed similar, distinct L-shaped size-class distributions. All six species were aggregated at small scales. The degree of aggregation of the three species with low abundance was in fact higher than that for the others at small scales. Aggregated patterns were also found for small and large trees at small scales. For spatial associations among the congeners, the goodness-of-fit (GoF) test revealed significant associations for only 10 of 30 species pairs, indicating no clear evidence for interspecific competition within them. In comparing the relationships among different size classes, we found no significant relationship for most of the analyzed species pairs. The GoF test detected significant associations for 6 of 20 species pairs among large trees of different species, 6 of 30 species pairs among small trees of different species, and 11 of 30 species pairs between large and small trees of different species. Based on a comparison of population structure, spatial patterns and associations, we infer that for these congeners there exists no significant difference in seed dispersal, competitive ability, or the requirement for specific topographic and light environments. Other factors (e.g., seed production and other habitat requirements) may contribute to the coexistence of these congeners and the trade-off between species commonness and rarity.