Fitossociologia e levantamento dos estratos herbáceo e arbóreo em estágios sucessionais no núcleo de desertificação do Seridó.

Abstract

The study of phytosociology allows us to recognize and define the structure, dynamics and classification of a plant community through quantitative parameters of a specific plant community, determining the frequency, abundance, dominance relationship and relative importance of certain species. This study aimed to characterize the shrubs and herbaceous vegetation found in areas of Caatinga by phytosociological analysis and natural regeneration of the species. The study was conducted at the Cachoeira São Porfírio Farm, in Varzea, PB, where three study areas with vegetation in different stages of regeneration were selected. For the phytosociological sampling three permanent plots with an area of 100 m² (50 mx 20 m), systematically distributed in limited areas, in each regeneration stage were installed. For each area, the Shannon diversity index (H '), Simpson dominance index (C) and the evenness through the evenness index by the Pielou index (J) were calculated. For all trees, circumference measurements at breast height (CAP) and total height were taken. In the area in succession in the primary stage, 52 individuals were sampled divided in two families and four species, whereas in the area in succession middle stage 140 individuals were sampled in divided in two families and five species and in the succession in the advanced stage, 296 individuals were identified, two families and six species. The Fabaceae and Euphorbiaceae families stood out in numbers/quantity. Poincianella pyramidalis and blanchetianus Croton Baill had a greater number of individuals in the areas under study. The late successional stage showed higher diversity index of Shannon-Weaver (H ') with 1.69 nats.ind-1. The pyramidalis Poincianella and Croton blanchetianus Baill species had higher frequencies, densities, dominances and importance value index. In the three areas most species are in the height class in from 1.5 m to 4.0 m. For the study of herbaceous stratum, 27 subplots of 2m radius in each study area were marked. We conducted a census of all species in the study area, measuring the height and diameter. We identified 49 species, distributed in 18 botanical families and 34 genera. The families richest in species were Euphorbiaceae and Fabaceae. The species with the highest density, occurrence and importance value of herbaceous populations were the Croton blanchetianus Baill., Diodella teres and Waltheria indica. The diversity by ShannonWiever index was 2.52 nats.ind-1 to the area in early successional stage. The physiognomy of herbaceous stratum was marked by the species Croton blanchetianus Baill., Diodella teres and Waltheria indica, being these species the ones with larger numbers of individuals in the study area.