STRUCTURE AND DIVERSITY OF THE THREE PLANT ASSOCIATIONS IN THE SAN JUAN RIVER DELTA, CHOCO, COLOMBIA

The forests of the Pacific Coasts of Choco are timber suppliers for Colombia. The floodable plant associations have been poorly investigated. To contribute with ecological basis for their management, the aim of this study was to learn about the differences between the forests of three physiographies and how the flood level explains them, comparing these forests with other of the neotropic. Three parcels of 0.5 ha were stablished y and individuals with DBH >= 10 cm were measured. The most common species is Oenocarpus bataua in well drained zones and Campnosperma panamensis in permanently flooded or swamp. The principal components analysis separated the three communities; the first and the second components explained 48% and 26% of the total variation, respectively. There is a high species richness and density of small and medium tall trees in the terrace and hill, in contrast with the low richness in the swamp zone with hyperdominance of one species and a bigger basal area. The dominance of species well adapted to stress caused by hydric excess in the swamp evidenced an environmental filter, that determines a composition and structure particular in the swamp. The studied forests have particular characteristics that differentiate them from other forests of low tropical lands, in particular, a high tree density, less species richness and lower mean wood density compared with Amazonia forests.