Composição florística e estrutura de fragmentos florestais na área de influência do reservatório da usina hidrelétrica (UHE) de Tucuruí, Pará, Brasil.

Abstract

The increase of the population human being and its activities has resulted in the destruction, degradation and fragmentation of habitats to such point that this process is now the biggest cause of the decline of biodiversity. The areas of interest of this study shelter attacked stretches sufficiently environmentally, had the dam of the river Tocantins for formation of the lake of the Plant hydroelectric of Tucuruí, where if they had formed you vary islands of vegetation in the tops of mounts, presenting great importance for representing part of the areas that had been submerged. The research had as objective to know the floristic, phytosociology composition and structure of the wood stratum of the fragments, esteem the diversity of the same ones and to analyze the floristic similarity between fragments of one same edge and different edges. The Plant hydroelectric of Tucuruí is located in the southeastern of Pará in the City of Tucuruí on the geographic coordinates 03º45'58”S and 49º40'21 " W. The areas where the parcels had been placed you show, had been selected on the basis of the information deriving of the interpretation of images of satellites. After definition of the sampling areas had been installed permanent parcels of 100m x 100m (1 ha), divided in 25 sub-parcels of 20 m x 20 m, in each sub-parcel, had been registered all the individuals with diameter to the height of the chest ≥ 10 cm. For phytosociology analysis had been used the classic parameters of Abundance, Frequency, Dominance and the Value of Importance calculated through the program Native Bush. The diversity was calculated through the Shannon-Weaver Index and the Equability of Pielou. The floristic similarity was esteem through the index of Jaccard and Sorensen. For the four hectares a total of 1.720 individuals were found, between trees, palms and lianas, distributed in 49 families, 156 sorts and 305 species. The number of families and species between the samplings varied of 32 the 43 and 76 the 156, respectively. The number of exclusive species between the fragments in accordance with varied the total number of species, the difference between each sampling is more significant between that they possess greater difference in the total number of species and when this difference is lesser this number almost does not differ. It enters the five more representative families in number of species for sampling Fabaceae was present in all, Mimosaceae was enters most representative in three, Sapotaceae, Chrysobalanaceae and Lecythidaceae had been most representative only in sampling III. For the comparative analysis she enters the families with bigger wealth of species and number of individuals, verified itself that she has a direct relation between them, where some families of bigger wealth in the samplings, they are between that possess the biggest numbers of individuals. Cenostigma tocantinum inside presented high density of three samplings, mainly in sampling IV, however absent of sampling III. One of the factors that if can lead in consideration for the absence of this species are the localization of the samplings, therefore this if only finds of the continent, thus making it difficult the circulation of possible dispersive more distant of this species. Sampling III presented the biggest index of diversity (4,40) and sampling I the minor (3,55). The indices of equability for samplings I, II and III, present well next values, evidencing low a dominance of the species for these samplings. In it analyzes of the curves species-area samplings I, II and IV showed that one hectare was enough for characterization of the same ones, however for sampling III the curve did not stabilize, showing that one hectare was not enough its characterization. The species that had presented the biggest value of basal area had been, for sampling I and IV Cenostigma tocantinum (5,878 m2/ha and 14,759 m2/ha), for the sampling II Alexa grandiflora (4,199 m2/ha) and for the sampling III Bertholletia excelsa (5,298 m2/ha). Analyzing the phytossociological parameters of the samplings it was observed that more than 80% of the species present value of importance below of 3%, these results show that each species contributes equally for the diversity of the fragments. For the distribution of the individuals in classrooms of diameters, the curve presented the classic form of “inverted J” for all the samplings. It enters the samplings the biggest values of similarity had been registered for samplings I and II and the minors for I and III, all below of 25% in the index of Jaccard. The results of the studies had shown that the studied fragments had presented differences with regard to the number of families and species, demonstrating the existence of difference in the floristic composition of the fragments, even so these are inserted in the same floristic matrix and also differences in the structure of the fragments.