Análise estrutural de duas fitofisionomias de caatinga em diferentes estados de conservação no Semiárido Pernambucano.

Abstract

The objective of this work was to carry out a comparative study of the phytosociological structure of two fragments of caatinga located in the Experimental Station of Embrapa Semiárido, Municipality of Petrolina - PE, and with this to generate essential knowledge to support actions of conservation and management of the vegetation of this biome. In the two selected areas (Area I: which was cleared 30 years ago and since then has been recovering without intervention anthropica and Area II: fragment of caatinga with a history of less anthropization), a floristic-phytosociological survey was carried out using the plot method. In each fragment, 10 sample units were plotted, randomly distributed. All individuals with Diameter at breast height (DBH) ≥ 3 cm were inventoried, in addition to measuring the Diameter at ground level (DNS) and their total height according to the inclusion criteria. The vegetation structure was evaluated using the usual parameters. For each area, the Shannon diversity index (H') and the evenness were calculated using the Pelou index (E). The analysis of dysmetric and hypsometric distributions was performed with intervals of 3 cm and 1 m, respectively. To verify the pattern of spatial distribution of species in the area, the Payandeh Aggregation Index (Pi) was used. To analyze the similarity, we used the Jaccard index (agglomerative method of arithmetic means), the Euclidean distance using the Ward method and Multivariate Analysis using the PC-Ord program. In Area I, 432 live individuals distributed in 8 families, 10 genera and 16 species were sampled. In Area II, 296 individuals belonging to 11 families, 9 genera and 25 species were inventoried. The families that presented the highest number of species in the two areas were Mimosaceae, Caesalpiniaceae and Euphorbiaceae. The most abundant taxon in Areas I and II was Mimosa tenuiflora. The most abundant taxa were also the most important in the structural assessment in the two communities. The diversity index and equability in Area I were 1.39 and 0.50, respectively, whereas in Area II they were 2.52 and 0.78, respectively. From the frequency distribution of individuals in diameter classes, the typical trend of uneven natural forests was observed, close to the "inverted J" model, while the hypsometric frequency distribution showed that most individuals are small. In the spatial structure, in general, it can be observed a great participation of plant species with "aggregated" pattern or with "tendency to aggregation" in both areas. Through the analysis of similarity and principal coordinates, the formation of three distinct groups was observed. The results showed that the studied areas present differences both in physiognomy and structure, a floristic richness compatible with caatinga environments and that the fragments are in an initial stage of succession (area I) and intermediate (area II), with a tendency to recover, if no significant disturbances occur.