Levantamento florístico e fitossociológico de uma floresta estacional no domínio da Caatinga em Castro Alves - Ba

Abstract

This study aimed to analyse the structure of a fragment of seasonal forest at Castro Alves, Bahia, northeastern Brazil. The study area represents 24 hectares and four permanent parcels of 2,000 m2 each were systematically investigated. These transects were divided into 40 plots of 10 x 20 m. All individuals with the stem diameter at ground level (DGL) ≥ 5 cm, excluding lianas and dead individuals, were labelled with aluminium tags, numbered, and measured according to its DGL. Botanic sample materials of the measured individuals were collected for further herborization and identification following Angiosperm Phylogeny Group III. It was calculated by species the absolute density, relative density, absolute frequency, relative frequency, absolute dominance, relative dominance, importance value index (IVI), and cover value index (CVI). The Shannon’s diversity index and Pielou's evenness index was calculated and the degrees of freedom for the basal area and the number of individuals per hectare were obtained by the method of successive differences. A total of 1,049 individuals, 29 botanical families and 74 species were present in the study area. The most representative family in number of species was Fabaceae with 19 species and 10 of the 29 families were represented by only one species and seven individuals were not identified. The species most representative in density and dominance were Sideroxylon obtusifolium (IVI = 34,42 %), Capparis yco (IVI = 26,15 %) and Astronium concinnum (IVI = 23,02 %). Shannon’s diversity within the sampled fragment was 3,42 nats.ind-1 while Pielou’s evenness was 0,79. The degrees of freedom for the basal area (m2.ha-1) and density (n.ha-1) were respectively: P (11,9≤ μ≤14,15) = 0,95 and P (1.294≤μ≤1.329)= 0,95. It was clear that the diversity index found in this study is in agreement with other studies done in the Caatinga in which the values were from 2-3 nats.ind-1. These results will serve as background data for the elaboration of conservational strategies in the Caatinga biome.