Status da vegetação de caatinga após a implantação das obras de integração do Rio São Francisco com bacias hidrográficas do nordeste setentrional

Abstract

The Project of the San Francisco River Integration- PISF corresponds to a venture that aims to integrate watersheds carrying water for the local semi-arid northeastern suffering from drought. The idea of this research arose because of the low or total absence of information generated by government agencies about the real situation that we find the works of PISF, especially with regard to the changes experienced by the vegetation of the Caatinga. The study was conducted in the municipality of Sertânia-PE, located in the microrregion known as Moxotó Pernambucano (08 ° 04'14''S, 37 ° 15'37''W, average elevation of 558 m). On the banks of a canal PISF were arranged at random, five transects perpendicular to it (direction channel-vegetation). In each of these, were plotted 10 plots of 20 m x 10 m (the smallest dimension being parallel to the channel), making a total sample area of 1 ha. Within the sampling units, all individuals were counted and their diameters were measured at ground level. Individuals, who had DNS ≤ 3 cm were considered regenerating, while those who had DNS> 3 cm in adults. For each ontogenetic stage were calculated density, diversity index and Shannon-Weaver evenness by Pielou's index. Numbers of individuals and species were compared between the distances of the channel through the Kruskal-Wallis, diversity differences by t test, Pearson correlation coefficient, the Jaccard similarity index and coefficient of Bray-Curtis distance. In the survey 3.685 individuals were sampled, being 2.288 regenerating and 1.397 adults, belonging to 32 species, 30 genera and 15 families. The most representative families were Fabaceae and Euphorbiaceae and the species Sida cordifolia, Croton blanchetianus and Mimosa ophtalmocentra were the most representative. The species Nicotiana glauca, Calotropis procera, Urena lobata, Sida cordifolia, Herisssantia tiubae and Cleome spinosa tend to diminish their importance somemk extent to vegetation converge to the most advanced seral stages, since these species colonize degraded areas of the border. We observed the formation of two large groups, which were located at a distance of approximately 0-100m, almost completely matched the regenerating individuals, and the other was inserted in the 100m to 225m which was represented in large quantities by adults. In this last group we observed a considerable increase over the average number of species and individuals. With these parameters it is evident that the works of the PISF are causing impacts beyond those already anticipated such as the local reduction of phytodiversity, place the formation of vacant niches and establishment of exotic species.