Floristic and tree structure of forest islands in savanna areas of Northern Brazilian Amazonia

Abstract

Forest islands are isolated forest fragments found in Amazonian savanna-forest transition zone of the neotropics. Information on tree communities of these formations is necessary to establish conservation policies which protect these paleoclimatic forest remnants. A forest inventory was carried out in tree communities of four seasonal forest islands in the savanna of Roraima, northern Brazilian Amazon. Two islands were defined as small (5-10 ha), one as medium (10-20 ha) and one as large (20-60 ha). All islands were disturbed by selective logging and fire. We sampled 470 individuals with diameter at Breast Height (DBH) ≥ 5 cm comprising 52 species, 41 genera and 25 families. The most species-rich families were fabaceae (11) and sapotaceae (6). Most species were pioneers (55.8%). Abarema jupunba (fabaceae) and Chrysophyllum argenteum (sapotaceae) were common in the four fragments. Greater floristic similarity was detected between the medium and large islands. Intensity and time scale of post-disturbance strongly influence tree community dynamics, and obscure a clear pattern between horizontal structure (number of individuals, DBH and basal area) and size of forest islands, although fragment size significantly affected species richness and diversity.