Composição florística e estrutura de um fragmento de mata atlântica em Pedra de Guaratiba, município do Rio de Janeiro, RJ

Abstract

The results of a floristic and phytossociological survey of the tree layer in an area of Atlantic Rainforest in the Environmental Protection Area of Serra da Capoeira Grande, Rio de Janeiro municipality, Rio de Janeiro State. The site lies near the State Park of Pedra Branca and is the last forest remnants in the municipality where brazilwood (Caesalpinia echinata Lam.) occurs naturally. The arboreal individuals were sampled according to the quadrat method. The inclusion criteria was perimeter at breast height of 15cm or more. A total of 200 points were surveyed, resulting in a sample of 800 individuals. The floristic composition comprised the taxonomic identification of the sampled individuals and of species coleted during excursions inside the forest, in the sampled area and the surroundings. Considering only the phytossociological sampling, 43 species were identified, belonging to 36 genera and 24 botanical families. By adding the species found in the ramdon collection to these values, a total of 68 especies was obtained, comprised in 57 genera and 31 families. The families with the most species were Leguminosae Mimosoideae with seven, Myrtaceae with six, Euphorbiaceae and Leguminosae Papilionoideae with five and Bignoniaceae, Bombacaceae, Celastraceae, Flacourtiaceae, Moraceae, Rubiaceae and Solanaceae with three. The families with the higher importance value indices (IVI) were Solanaceae (34.1), Leguminosae Mimosoideae (16.4), Nyctaginaceae (13.0), Leguminosae Papilionoideae (7.9), Anacardiaceae (6.5) and Flacourtiaceae (6,1), this six families together accounted for 84% of the total IVI. The species with greater number of individuals were the same with higher IVI. They are: Metternichia princeps with 40.4% of the individuals and 33,7% of the total IVI, Pseudopiptadenia contorta (9.3 and 12.6%), Guapira hirsuta (7.5 and 7.8%), Guapira oposita (4.6 and 5.3%), Casearia obliqua (4.6 and 4.2%), Pterocarpus rohrii (3.6 and 4.3%), Albizia policephala (3.5 and 3.5%) and Aspidosperma subincanum (3.4 and 3.6%). Caesalpinia echinata followed with 2.4% of the individuals and 2.1% of the total IVI. The forest has an almost continous tree strata, plus the emergent trees which may achieve 18m. Trunk diameters of the individuals are concentred in the smallest classes. Diameter distribution of the most important species sampled indicate abundant regeneration and stable population structure. The Shannon diversity index is 2.42 and the equability 0.636. Comparing the floristic composition of EPA of Capoeira Grande and 19 other forest areas in Rio de Janeiro State, floristic similarity was observed between the studied forest and those near the sea and whith lower altitudes. All forests were agruped with low index of similarity, showing the high biological diversity of Rio de Janeiro forests.