Levantamento da cobertura vegetal e estudo fitossociológico da Floresta Nacional de Caxiuanã - PA.

Abstract

This research had objective to survey the vegetation of the Caxiuanã National Forest and characterize the terra firme (high ground) vegetation by analyzing floristic diversity and horizontal structure. The survey of vegetation was made from visual interpretation of Landsat TM 5 images in black and white, orbital/point 225/061 - C and 225/062 - A, at a scale of 1:100.000 on band 4, with the date reference of 14/08/91. The information extracted was introduced into a Geographic Information System to generate a map of the area's vegetation. Field data was obtained by undertaking a forest inventory covering the entire area of terra-firme forest. Random samples of conglomerates in two stages were used, with surveys of 51 hectare. All trees with a DBH ≥ 25 cm were identified botanically and DBH measurements were registered. A Grouping Analysis of the conglomerates was made, classifying them into three groups. Floristic diversity was analyzed according to Simpson's index of dominance, Simpson's index of diversity and Shannon-Weaver's index of diversity, and Equability. The horizontal structure of the forest was analyzed by considering diametric distribution of the trees, dominance, abundance and frequency of species and the Importance Value Index according to the ordering techniques for the Main Components Analysis. The phyto-physionomic survey, made by interpreting orbital images, identified 5 classes of vegetation, showing that 75% of the vegetation is represented by Dense Broadleaf Forest with emergent trees. The Grouping Analysis identified three groups of conglomerates that form distinct units in relation to the diametric structure, density and floristic richness. In the entire sampled area, 6,923 individuals with a DBH ≥ 25 cm were registered, distributed in 45 families, 135 genera and 189 species. In Group 1, the individual trees were distributed in 43 families, 133 genera and 184 species, group 2 in 38 families, 88 genera and 116 families and group 3 in 39 families, 91 genera and 116 species. In the whole sample area and within the three groups the Caesalpiniaceae family showed the greatest species richness. xvi The total area of the three groups studied had high diversity, low concentration for dominance and high equability. In relation to the diametric distribution, it was observed that the number of individuals diminished as the diameter class increased, giving evidence that the cubic model fitted best to the diametric structure of the trees in the whole area and in groups 1 and 2. While in group 3 the cubic - root model suited the diametric structure the best. Eschweilera parviflora is the most abundant and dominant specie in the whole area and in three groups studied. Ocotea myriantha is the specie with the greatest frequency in the whole area. In grupo 1, the most frequent species are: Ocotea spp, Parkia auriculata and Eschweilera parviflora. In group 2 Vouacapoua americana, Parkia auriculata, Inga spp, Ocotea myriantha, Eschweilera parviflora, Geissospermum sericeum, Minquartia guianensis and Licania latifolia, are the most frequent species. In the group 3, the most frequent specie is Guatteria sp. The specie Eschwielera parviflora is the most important in the horizontal structure of the forest, both for the analysis of the whole area, and the three groups studied.