Scale-Dependent Relationships Between Treefalls and Species Richness in a Neotropical Montane Forest

Recent community studies found no relationship between treefall regime and species richness at the scale of individual treefalls. Here, spatial patterns of trees >5 cm diameter and treefalls (mostly dated by using dendroecological techniques) were described in 6 ha of subtropical montane forest in northwest Argentina, to explore the relationships between treefalls and tree community composition at different spatial scales. Time since gap formation showed spatial autocorrelation at spatial scales smaller than 5000 m2 (Moran's I coefficient). Point pattern analysis (Ripley's K function) showed that very recent treefalls (1990–1997) are spatially associated with previous treefalls (1978–1987) at scales of 1000–5000 m2. At the scale of individual treefalls (100–400 m2), species richness was uncorrelated with treefall regime, and shade-tolerant and light-demanding species were not discriminated in a multidimensional scaling ordination analysis. However, correlation between treefalls and species richness, and the discrimination of regeneration groups, increased abruptly at the scales of treefall aggregations. In agreement with previous studies, this study suggests that isolated treefalls have little effect on species composition and diversity, probably due to recruitment limitation. Instead, this study shows that at scales >1000 m2, treefall regime is a good predictor of species richness and composition of regeneration groups. This may be because treefall aggregations and gap expansion increase the probability of new nearby treefalls being colonized by light-demanding species. These results emphasize the importance of scale and spatial dynamics of disturbances and species dispersal in the study of canopy disturbances and their effects on community composition and diversity.