Estrutura e diversidade da vegetação de caatinga em áreas serranas no trópico semi-árido paraibano

Abstract

The biodiversity hotspots altitudinal gradients in Brazil is little studied. On Northeast of Brazil and especially in the many semiarid mountainous areas are found and apparently function as refuges for the vegetation of the Caatinga present themselves as obstacles to the natural anthropogenic. The need to evaluate phytodiversity contained in the two fragments of vegetation found in the hills of Fontainha (7°28'74'' S and 36º23'47'') in Cabaceiras and mountain Bonita (07°44'42"S and 36°02'56") in Alcantil through its quantification as well as understand the structural organization of plant communities, due to altitudinal variations became the objective of this work. The study took place between November 2010 to May 2011, to sample the plant community in the mountains, was adopted the method of point-and-quadrant. In each saw 30 sampling units were chosen (Transects) each unit divided into six points, which are distant from each other 10m. The transects were distributed to separate altitudinal gradients. In all points were measured diameter at ground level and height, being the inclusion criteria for individuals to height (h) ≥ 1 m diameter at the soil (DNS) ≥ 3 cm. For the hierarchical classification of taxon was used Angiosperm Phylogeny Group II system (APG II, 2003). For analysis of the composition floristic and phytosociological parameters we used the software Mata Nativa (CIENTEC, 2002). The data were analyzed to allow comparison of composition and structure between the gradients of the same hill as well as between the same gradient of different saws. The families most conspicuous in both areas were Euphorbiaceae and Fabaceae. In mountain Bonita and Fontainha showed the greatest importance value was Croton blanchetianus fact that shows the success ecology of the species characterized by its high frequency in the sampling units. The other species with the most obvious values for the parameters phytosociological were Poincianella pyramidalis, Mimosa sp. Aspidosperma pyrifolium, stipulaceae Piptadenia and Mimosa hostilis, species typical of these degraded areas. There were differences in diversity and structure of vegetation in relation to altitudinal gradients, and the areas top the most conserved in this study. Thus, for the study area the vegetation in mountain ranges not necessarily the best preserved in semiarid, as the parameters evaluated here showed, these fragments of mountain range, with a richness and vegetation low diversity compared with other fragments of scrub and there influence of altitude on the composition and diversity of these mountainous areas.