Florística e fitossociologia da caatinga arbórea nas ecorregiões do Estado da Paraíba.

Abstract

The wide extension of the semiarid region of northeastern Brazil favors the diversity of its edaphoclimatic characteristics, which in turn determine fauna and flora diversity of the Caatinga biome. The different features and particularities of the region determined its division into eight ecoregions with geographical limits related to the characteristics of climate, altitude, relief and soils, which are fundamental for understanding the complexity of the biome. In Paraíba State, the Caatinga biome occurs in three ecoregions, whose characteristics interfere with the floristic composition and diversity. This study analyzed the caatinga tree vegetation present in these three ecoregions of the Paraíba State, correlating their species to the edaphoclimatic factors (precipitation and soil types) of each ecoregion, according to the data from the National Forest Inventory (IFN) carried in Paraíba provided by the Brazilian Forestry Service agency. The IFN methodology for data collection consisted of a 20 km x 20 km grid containing a conglomerate in each intersection, each conglomerate composed of four 20 m x 50 m plots, subdivided into 10 10 m x 10 m subplots. These plots, located according to geographic coordinates, were used for measurements (height and diameter at breast height DBH) and counting of tree individuals with DBH equal to or greater than 10 cm, and collection of fertile material for taxonomic identification of the species. All regenerating individuals with DBH of less than 5 cm were also counted in 5 m x 5 m subplot determined for this purpose. The geographic coordinates used at each collection point were plugged into the ArcGis geoprocessing software and located on the State map according to the ecoregions present in Paraíba [Sertaneja Northern Depression (SND), Sertaneja Southern Depression (SSD) and Borborema Plateau (PLA)]. Then, these points were correlated with the soil types and rainfall ranges, as well as studies on the phytosociological parameters of the plant communities in their respective ecoregions were performed. Data analysis showed that of the 126 conglomerates in the Paraíba caatinga area, 70, 11 and 45 were located, respectively, at the SND, SSD and PLA ecoregions. A total of 1303 trees, classified in 60 species and 23 botanical families, were inventoried. The phytosociological parameters showed that the SND ecoregion has higher richness, followed by the PLA and the SSD ecoregions, respectively, with 2.94, 2.85 and 2.40 nats.ind1. The analysis of the correlation of precipitation ranges and soil types with richness of species and abundance of individuals suggests that these parameters may be more influenced by soil types than by the different precipitation ranges. The SND and the PLA ecoregions showed peculiarities in their ecosystems by presenting species of exclusive occurrence. Probably, in this study, richness of the caatinga was underestimated because it was restricted to trees with DBH > 10 cm.