Florística e fitossociologia do componente herbáceo em uma área de caatinga no estado da Paraíba.

Abstract

The Brazilian Northeast is occupied by the Caatinga. a vegetation that has adaptations that give it the ability to withstand droughts for long periods. The herbaceous species present in this vegetation possess characteristics of escape or tolerance to these conditions. However, this component has yet to be analyzed, especially when it comes to studies that accompany its seasonal transitions. Given this reality, the objective was to conduct a floristic and phytosociological survey of the herbaceous component in an área of Caatinga during the dry and rainy seasons. The study was conducted in the RPPN Fazenda Almas, located between the municipalities of São José dos Cordeiros and Sumé in the Paraiban Cariri region. A one hectare plot, subdivided into 100 subplots of 10m x 10m was established for the study. The floristic survey was conducted over a year in al1 100 plots. All herbaceous species, including "bryophytes and pteridophytes" were included. The phytosociological study was carried out in the rainy season in March, and the dry month of July. Thirty-ave subplots were randomly selected for the survey. The general flora (flora) had 27 families, 36 genera and 83 species. The most representative families were Malvaceae (12) Convolvulaceae (lO), Euphorbiaceae (8), Leguminosae and Asteraceae (6) and Poaceae (5). The phytosociological survey of the rainy season yielded 4332 individuais belonging to 19 families, 41 genera and 50 species. The families with the highest number of species were Convolvulaceae (8), Leguminosae (7). Malvaceae (6) and Euphorbiaceae (5). In the dry season 590 individuais were found belonging to 18 families, 30 genera and 38 species. The families with the highest number of species were Leguminosae (5), Asteraceae (4) and Poaceae (3). The taxonomic diversity in the rainy season and dry season was 4,986 and 4,934, respectively. Of the 62 species found in the phytosociological surveys (rainy and dry season), 22 were restricted to the rainy season, 13 the dry season and 27 co-occurred in both periods analyzed. Soil cover in the rainy season was 84.45%, while in the dry period was 32.23%. Precipitation, brightness and competition are possibly responsible for the change in the herbaceous component of the study área. However, even with large differences in species richness, the results of the taxonomic diversity showed no significant variation between the raíny and dry season. This shows that this component, although ephemeral, has strategies to withstand water stress conditions for long periods. This leads us to conclude that it is crucial to understand the richness and dynamics of this component for us to estimate accurately the diversity of Caatinga.