Landscape context and local-scale environment influence regeneration of pioneer tree species in treefall gaps

Composition of pioneer tree species was recorded for 23 to 76 treefalls in the forests of La Selva (LS), Barro Colorado Island (BCI), Cocha Cashu Research Station (CC), and KM41 to evaluate the hypothesis that distance to secondary forests influences the composition of pioneer tree species at scales of thousands of hectares and to assess the relative importance of distance to seed sources compared to two microenvironmental factors: soil and gap size. Discriminant function analysis (DFA) was used to assess the relative importance of the landscape and environmental factors in controlling the presence in gaps of Cecropia species that are typical of secondary forests regenerating after large-scale disturbances. Principal component analysis (PCA) was used as an ordination technique based on pioneer species composition of each gap. The PCA ordination axes were regressed against soil type, gap size, forest type, and distance values of each site to explore the relationship between composition and control factors. At the four sites, the variable best correlated to the discriminant function of gaps with and without Cecropia was the distance to secondary forests, although such discriminant function was statistically significant at only one site. In three of the four sites (with the exception of BCI, where there are no typical young secondary forests), distance to secondary forests was correlated with at least one axis of the PCA (P < 0.06). Other significant correlations included soil variables (CC and KM41), gap size (KM41), and forest type (secondary vs. primary; BCI). Overall, the results provide some support for the hypothesis that at the spatial scale of this study, distance to young secondary forests (both natural and anthropogenic) influences treefall gap composition at a level comparable to endogenous and exogenous microenvironmental factors.