6 ilus. 7 tab. 25 ref. Sum. (En)

Studies were undertaken on the floristic composition and stand structure of four 1 hectare plots in the lowland forests of Kurupukari, Guyana. A total of 3897 trees, covering 153 species and 31 plant families were 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 two/fold between study plots, with 45-50 percent of the trees within the 5-10 cm 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 percent of the total number of trees, while representing only 11.2 percent of the species. No one plant family dominated in more than one of the four study plots, and all four plots held at least one plant family with more than 20 percent of the total number of trees. Although 14 tree species were common to all four plots, only 26 percent/35 percent of the species were represented by a single tree. Between three and seven species represented 50 percent of the trees within all size/classes, with species dominance occurring within the highest density plot. These tropical forest types of central Guyana may represent some of the lowest diversity forests in the neotropics, whereby the total number of tree species is relatively limited, typically with six dominant canopy species, but the relative abundance of these species is highly variable between the forest types. Mechanisms influencing the competitive interactions associated with species dominance are discussed in relation to the importance of mycorrhizae and the persistence of species dominance.