We used point pattern analysis to examine the spatial distribution of 46 common tree species (diameter at breast height >10 cm) in a fully mapped
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‐m tropical forest plot in Sinharaja, Sri Lanka. We aimed to disentangle the effect of species interactions (second‐order effects) and environment (first‐order effects) on the species’ spatial distributions. To characterize first‐order associations (segregation, overlap), we developed a classification scheme based on Ripley’sKand nearest‐neighbor statistics. We subsequently used heterogeneous Poisson null models, accounting for possible environmental heterogeneity, to reveal significant uni‐ and bivariate second‐order interactions (regularity, aggregation and repulsion, attraction). First‐order effects were strong; overall, 53% of all species pairs occupied largely disjoint areas (segregation), 40% showed partial overlap, and 6% overlapped. Only 5% of all species pairs showed significant second‐order effects, but about half of the species showed significant intraspecific effects. Significant plant‐plant interactions occurred mostly within 2–4 m and disappeared within 15–20 m of the focal plant. While lack of significant species interactions suggests support for the unified neutral theory, species’ observed spatial segregation does not support the assumptions of the neutral theory. The strong observed tendency of species to segregate may have supplementary effects on other processes promoting species coexistence.
Fully mapped tree census plots of large area, 25 to 52 hectares, have now been completed at six different sites in tropical forests, including dry deciduous to wet evergreen forest on two continents. ...One of the main goals of these plots has been to evaluate spatial patterns in tropical tree populations. Here the degree of aggregation in the distribution of 1768 tree species is examined based on the average density of conspecific trees in circular neighborhoods around each tree. When all individuals larger than 1 centimeter in stem diameter were included, nearly every species was more aggregated than a random distribution. Considering only larger trees (≥ 10 centimeters in diameter), the pattern persisted, with most species being more aggregated than random. Rare species were more aggregated than common species. All six forests were very similar in all the particulars of these results.
The degree of aggregation in the distribution of 1768 tree species, based on the average density of conspecific trees in circular neighborhoods around each tree, was examined in six tropical forest ...sites in Panama, Malaysia (Peninsula and Borneo), Thailand, India, and Sri Lanka. The sites encompassed a range of tropical forest types and contained large (25-52 ha), fully mapped tree census plots. Results showed a nonrandom degree of aggregation for almost all tree species, when all individuals with a stem diameter >1 cm were included. The pattern persisted when only trees greater than or equal to 10 cm in stem diameter were considered, although in most species aggregation intensity weakened somewhat at these larger sizes. Aggregation was stronger in rare than in common species. The observed patterns were very similar in all six forests.
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