Florística e fitossociologia do banco de sementes em área de caatinga no Núcleo de Desertificação do Seridó, na Paraíba.

Abstract

The seed bank in the soil is one of the most efficient mechanisms in the conduct of natural regeneration in terrestrial ecosystems, and their study is an important tool used to diagnose the effect of degradation. This study aimed to analyze composition floristic and phytosociological seed bank in the soil at different stages of natural regeneration in semiarid Caatinga of Paraíba. The study was conducted at Fazenda Cachoeirade São Porfírio in the municipality of Varzea, PB, where four areas were selected, one with native pasture and three in different stages natural regeneration vegetation. For sampling the seed bank in the soil were randomly collected 144 samples at three different times, and the methodology used to determine the floristic species composition of the seed bank in the soil was the seedling emergence. To assess the floristic diversity were estimated diversity index Shannon-Weaver (H '), equability index for Pielou (J'), Similarity and Jaccard (Sj) . For phytosociological analysis the following parameters were evaluated: Absolute Frequency (AF) and Relative Frequency (RF), Absolute Density (DA) Relative Density (RD) and Total Density (TD). The experimental design was a randomized block factorial design (4 x 3 x 2 x 2). The floristic composition of the seed bank in the soil of the study area this represented by 94 species belonging to 71 genera, distributed in 29 botanical families. The soil seed bank of the study area consists predominantly of species of herbaceous habit, and the floristic composition varies according to the stage of natural regeneration, higher in middle and advanced stages. Between the factors studied, the factor area and seasons were the ones who had significant differences (p<0.01). The seed bank in the soil showed seasonal variation, recording the highest values of seedling emergence in the rainy season. The average density of the seed bank was higher in the soil with 5,066 seeds/m2 and 3,939 seeds/m2 in the litterfall. The seed bank in the soil of the area with native pasture showed higher densities of plantlets.