TREE POPULATION STUDIES IN LOW-DIVERSITY FORESTS, GUYANA .1. FLORISTIC COMPOSITION AND STAND STRUCTURE

Studies were undertaken on the floristic composition and stand structu re of four 1 hectare plots in the lowland forests of Kurupukari, Guyan a. A total of 3897 trees, covering 153 species and 31 plant families w ere recorded at greater than 5 cm diameter at breast height (dbh). The number of species per hectare ranged from 61 to 84 (> 5.0 cm dbh) and 50-71 (>10.0 cm dbh). The total number of trees per hectare varied tw o-fold between study plots, with 45-50% of the trees within the 5-10 c m size-class. Mean total basal area varied from 32.39-34.63 m2 per 100 m2. The four most dominant plant families represented 43.8% of the to tal number of trees, while representing only 11.2% of the species. No one plant family dominated in more than one of the four study plots, a nd all four plots held at least one plant family with more than 20% of the total number of trees. Although 14 tree species were common to al l four plots, only 26%-35% of the species were represented by a single tree. Between three and seven species represented 50% of the trees wi thin all size-classes, with species dominance occurring within the hig hest density plot. These tropical forest types of central Guyana may r epresent some of the lowest diversity forests in the neotropics, where by the total number of tree species is relatively limited, typically w ith six dominant canopy species, but the relative abundance of these s pecies is highly variable between the forest types. Mechanisms influen cing the competitive interactions associated with species dominance ar e discussed in relation to the importance of mycorrhizae and the persi stence of species dominance.