Composição e estrutura do banco de sementes de fragmentos de caatinga em diferentes estágios de conservação.

Abstract

Composition and structure of the seed bank of fragments of caatinga in different stages of conservation. Seed bank studies in areas with different levels of dry forest conservation are essential for determining species richness and understanding the impacts of anthropogenic interventions on ecosystem equilibrium. In order to evaluate the richness, floristic composition and similarity of the seed bank between the two, it was sought to develop this work in two caatinga fragments, one anthropic and one in preservation. Fifteen 20 x 20 m plots were systematically distributed in each area, and two sub-plots of 1 m2 were installed in the interior, where 8 iron cylinders of 7.2 x 5 cm, for the collection of soil samples. The seedling emergence method was used to follow the germination of seed bank species. At the end of 6 months of soil incubation, 64 species were identified, distributed in 27 botanical families. The total density was 6,418.6 individuals / m2 considering both areas. In the preservation area the density was 3,434.4 individuals / m2, with 55 species and 26 families, while the altered area was 2,984.2 individuals / m2, with 53 species and 25 families. Both areas were composed mainly of herbs, with 91% and 93% of the species, and 99% and 93% of the individuals in the preserved and altered areas, respectively. The Shannon-Wiener diversity index was 2.47 and 2.34 and the Pielou equability 0.62 and 0.58 for the altered and preserved areas, respectively. The floristic similarity between the areas was 81% and 69% according to Sorensen and Jaccard. The phytosociological structure of the areas indicated the species Pilea microphylla, Mollugo verticillata, Oxalis divaricata, Phyllanthus niruni, Cyperus uncinulatus, Lipocarpha humboldtiana, Cyperus odoratus, Fimbristylis miliacea, as common to both areas in important phytosociological positions, but with variations in them. Rotala ramosior and Mitracarpus baturitensis were species with exclusive importance to the area in preservation, while. Scoparia dulcis and Portulaca elatior only in the anthropized area.