DIVERSITY, SIZE COMPOSITION AND SPATIAL AGGREGATION AMONG TREES ON A 1-HA RAIN-FOREST PLOT AT LA REUNION

Because lowland rain forests of oceanic islands have almost always bee n destroyed soon after human colonization, there exist few quantitativ e descriptions of tree species composition and diversity in such fores ts. For this reason, the diversity and structure of a lowland tropical rain forest were studied on a 1-ha permanent plot on the oceanic isla nd of La Reunion. A total of 1270 individuals of gbh greater than or e qual to 25 cm (girth at breast height), including at least 43 species, were mapped, measured and identified. Several species were represente d only by large individuals. Ten species among the 23 common enough to test are randomly distributed over the hectare, while 13 show aggrega ted spatial distributions. The tree species diversity, size structure and spatial distribution observed in this island plot are discussed in light of patterns occurring in continental lowland tropical rain fore sts. In the study area, the high density of trees and the tendency of conspecific individuals to be clumped may be linked to several factors : hurricane disturbance, lack of seed dispersers and patchy seed rain.