Community Structure of Woody Plants of Roraima Savannahs, Brazil

Abstract

Patterns of diversity and community organisation of woody species ofsavannahs in Roraima, northern Brazil, were investigated, to relate structuraldata with edaphic factors and to analyse floristic relationships usingclassification and ordination techniques. The species studied refer to aninventory of 45 plots of 150 × 10 m (0.15 ha)distributed in the Roraima savannahs. We identified 13,410 woody individuals,belonging to 30 families, 52 genera and 71 species. The percentage of rarespecies is high, 58%. The richness, diversity, density and basal area of thestudied plots suggest that Roraima savannahs are poor in species. The mostimportant species include element dwarf shrubs (Byrsonimaverbascifolia, Tibouchina aspera andCassia obtusifolia), shrubby (Psidiumguianense, Randia formosa, Caseariasylvestris, Erythroxylum suberosum,Tocoyena formosa and Mimosamicrocephala) and arboreal (Curatellaamericana,B. crassifolia, B. coccolobifolia,Bowdichia virgilioides, Roupalamontana, Antonia ovata, Genipaamericana, Vitex schomburgkiana,Peltogyne campestris, Xylopiaaromatica and Himatanthus articulatus).Correlation between edaphic factors and vegetation indices reveal that densityseems to be more sensitive to edaphic factors than to basal area and diversity.Density correlated significantly with levels of Al, K and the quantity of sandin the soil. Edaphic factors can explain the distribution and importance ofsomespecies, such as: B. virgilioides, R.montana and P. guianense. Classificationanalysis tended to confirm PCA results, separating Roraima savannahs into threelarge clusters. This suggests that ecological differentiation is based not onlyon species density but also on basal area. Ordination describes floristicvariation but does not identify all edaphic gradients.