A phytosociological study was carried out in 0.5 ha of remaining patches of 'Pre-Ama-zonian' humid tropical forest within the Sacavém Forest Reserve, located in the municipality of São Luís, state of Maranhão, Brazil (2° 32'S; 44° 17'W). The total area comprised of fifty 10x10 m quadrats in which 410 trees with a minimum perimeter at breast height (PBH) of 15 cm were sampled, including 5 dead individuals. There were found 110 species of 66 genera in 34 families. The DBH varied between 4.8 cm and 86.7 cm, with an average of 16.28 cm. The minimum, mean and maximum heights were 2.0 m, 11.16m and 25.0 m, respectively. The total basal area was 14.207 m2 or 28.4140 rrrVha with an average of 0,07 m2/tree; the absolute density was 820 trees/ha. The five most importante families in IVI were Leguminosae, Chrysobalanaceae, Meliaceae, Myrtaceae and Arecaceae, making up 49.24% of the total. The five most important species in IVI were Licania cf. incana Aubl., Guaina guidonia (L.) Sleumer, Copaifera langsdorffii Desf., Dipteryx lacunifera Ducke and one morpho-species (Unknown 1 ). As much as 60% of the species had only one or two individuals. The Shannon & Weaver diversity index (Η') was 4.189. Although the area studied is comparatively small, several comparisons made with surveys for other Amazonian forest locations led to the conclusion that the Sacavém Reserve has similar richness, density and dominance.
Phytosociology; 'Pre-Amazonian' forest; Sacavém Forest Reserve (São Luís, Maranhão)