Estrutura e florística da vegetação e do banco de sementes de um fragmento de caatinga.

Abstract

The vegetation of the Caatinga Biome, over the years, has been affected by anthropization, through the excessive use of its natural resources, without planning, which degrades a large part of its forests. The removal of degrading agents from an area is essential for the maintenance of species in the upper stages of succession, as well as to stimulate natural regeneration. Thus, this work aimed to evaluate the structure of the tree and shrub vegetation of adult individuals present in the area and the floristic composition of the seed bank of a caatinga fragment from Fazenda Lameirão in a state of conservation. The study of the phytosociological structure and floristic composition was carried out using demarcated transects, in which individuals were identified by the common name, and the diameter and height of trees, shrubs and regenerants were measured. In the phytosociological parameters of the horizontal structure, density, dominance; frequency and the importance value index. The proportionality of the species distribution in the area was analyzed using the Shannon­Weaver (H') and Pielou's Equality indexes. For the study of the seed bank, 92 soil + litter samples (13.8 m2) were collected, which were distributed in the CSTR/UFCG forest nursery for seed germination and monitoring of seedling development until flowering. The identification of the species was made through APGIV, 2016 and consultations in the specific literature. In addition to the floristic composition, the diversity and abundance of species was analyzed using the same indexes (Shannon­Weaver (H ') and Pielou's Equability) used for the structure. It is concluded that Mimosa tenuiflora followed by Croton blanchetianus, Bauhinia cheilantha, Cenostigma pyramidale and Combretum leprosum stand out in all studied phytosociological parameters. The diversity indexes are considered average for conserved caatinga areas. Diametric Class I concentrates the largest number of adult and regenerating individuals while there is a predominance of individuals in Class V for height distribution, as an effect of the absence of anthropization that favors the floristic composition and the continuity of large individuals in the upper strata of the fragment. In the seed bank, it is concluded that the studied caatinga fragment has a predominance of herbaceous species, with Panicum dichotomiflorum Michx and Cyperus esculentus L standing out, with about 79% of all individuals found in the samples. Mimosa tenuiflora (Willd.) Poir. it is the only tree recorded in the collected soil + litter, demonstrating its colonizing character and fulfilling its ecological role in the fragment. The diversity and wealth indices are low, despite the conservation condition of the area, and may reflect the disproportionality of the species' abundance and the number of individuals contained in them.