Estrutura e estágios de sucessão ecológica da vegetação de caatinga em ambiente serrano no cariri paraibano

Abstract

The Caatinga is the third biome most environmentally degraded, even as a semi-arid ecoregion unique in the world and of great biological importance to the Northeast. The savanna vegetation has a great variety of landscapes due to their wide spatial distribution. Studies on the succession dynamics of vegetation are important because they provide subsidies to the understanding of the complex distribution and relationship of living organisms in the environment. In order to broaden knowledge phytoecological Caatinga, this study was to analyze structural variation and diversity in relation to altitudinal gradients and in the application of multivariate statistical methods to characterize the stages of plant community development and composition of ecological groups . The study was conducted in Sierra Ignatius Pereira a dry forest sites belonging to Microregion Cariri eastern Paraíba. We plotted 30 plots of 50 x 4 m, systematically distributed in three altitude gradients: Gradient I (base), Gradient II (middle portion) and Gradient III (the top of the mountain), and inventoried all the species with the stem diameter ground level ≥ 3 cm and height ≥ 1m. The characterization of the structure of trees and shrubs was done from the calculation of the phytosociological parameters of frequency, density, dominance, importance value, margin. We also calculated the diversity indices Shannon - Wiener (H ') and evenness Jaccard (J). Analysis of community development and training of environmental groups was based on structural measures of sample and species by multivariate analysis of Principal Component Analysis (PCA) and Ascendant Hierarchical Classification and Cluster Analysis. The formation of environmental groups through multivariate statistical techniques have been faced with a classification of ecological groups based on light requirements for the development of species. The floristic composition cataloged in Sierra Ignatius Pereira had 2263 individuals in 44 species, 37 genera and 19 families, there was also an undetermined species. The families Euphorbiaceae, Fabaceae, Anacardiaceae and Cactaceae were most significant in numbers of individuals. The diversity index of Shannon-Wiener (H ') was 2.47 for the total area of the mountain. The total density found in this study was 3771 individuals. ha-1. The species with highest importance values (VI's) were Croton blanchetianus, Opuntia palmadora Bauhinia cheilantha Sapium glandulatum, Manihot glaziovii and M. urundeuva. The altitudinal gradients I, II and III showed subtle differences on the floristic composition and phytosociological parameters analyzed, although it was possible to distinguish the formation of two different gradients and Gradient I Junction Gradients' II and III. As the parameters analyzed for the development of the community were formed two groups associated with two phases: Phase transition and medium and early development. As for environmental groups, the cluster analysis provided the formation of five distinct groups. The division of environmental groups by multivariate analysis differed from the classification proposed in relation to light both in the number of groups formed as the species that compose them. The results of this study provided an important contribution to understanding the behavior and distributes the savanna vegetation along gradients of altitude environment formed by the mountains and on the degree of community development, however, about the formation of ecological groups in relation the structural parameters of the species, showed the need for more complex studies, involving a larger number of variables, which may further elucidate the patterns and ecological processes involved in ecological succession from savanna.