Estudo florístico e fitossociológico de um remanescente de caatinga à margem do rio São Francisco, Petrolina-Pernambuco

Abstract

The riparian vegetation along the São Francisco river has been suffering a strong degradation by the human action. As consequence exist a drastic reduction in the covering degree of the native vegetation and sediment deposition that has causing threatens own existence of the river. This study intends to contribute for the comprehension of the caatinga vegetation that happens in the margins of the São Francisco river, by the establishment of the relationships between topographical and pedological factors and distribution of woody plants. The floristic and phytosociological survey was carried out, during twelve months, in area of EMBRAPA-SPSB, in Petrolina-Pernambuco. Was open a transect starting from the margin of the river, with the length of 800 m, where 138 contiguous plots of 10 X 10 m were installed. In each plot was measured the stem at soil level (DNS) for all individuals, alive or dead, with diameter > 3 cm and total height > 1m. Along this transect a difference of 9,40m was registered and five topographic environments were identified: river side (MR), dike (D), floodable depression (DI), boundary terrace (TL), all of them belonging to the fluvial terrace, with Alluvial and Cambisol eutrophic silty soils and the inlander tableland (TS) with red-yellow silty texture Podzolic soil. Forty-eight species/morphospecies distributed in 39 genera and 21 families were identified. Four phytogeoenvironments, MR, D+TL, DI+TL and TS, were defined by environmental variations and the floristic similarity among the parcels, calculate using cluster analysis. The MR environment showed the largest total density, total basal area, maximum and medium height and maximum diameter, and besides also, presented 8,1% of the plants with superior height to 8m, against 0,6% of D+TL, 0,2% of DI+TL and 0% of TS. The species with the largest importance value index were Inga vera subsp. affinis in MR, Mimosa bimucronata in D+TL and DI+TL and M. tenuiflora in TS.