Composição florística arbórea e regenerante de matas ciliares em trechos urbanos de dois rios em Patos - Paraíba, Brasil.

Abstract

Civilizations have a close relationship with water courses. In addition to drinking water, many elements on its banks, such as areas suitable for agriculture and animal husbandry, favor the development of human activities. However, the occupation of riverside areas, which began with the removal of tree vegetation, reduces biodiversity and degrades the environment. The objective of this study was to characterize the floristic composition of tree species and the seed bank along the da Cruz and Espinharas Rivers, in Patos-PB, Brazil. Data collection was carried out in eight plots and in 32 subplots on the right and left banks of these rivers, in sites with tree vegetation located between the bridge of the Queiroz Supermarket and the bridge of the exit to Campina Grande via Alça Sudeste. In these plots and subplots, individuals of woody species (adults and juveniles) were characterized for height, diameter, family, genus and species, in addition to the density of individuals. The litter+soil collected from subplots was placed on a bench in the screened environment of the CSTR Forest Nursery, irrigated daily and monitored for seedling emergence, which were counted and characterized for growth habit, family, genus and species. Density, diversity (Shannon-Weaver Index - H') and distribution evenness (Pielou Index = J') of adult and regenerating individuals of woody species and plants that emerged from litter+soil were calculated. A total of 407 specimens of woody species were observed, with a low diversity of families for adults (2) and juveniles (5). From the litter+soil sampled material, emerged plants totaled 3,146 individuals, distributed in 23 botanical families, 39 genera and 46 species. From that total, 1404 were shrubs, 1272 herbs and 390 tree species, from which 362 individuals were of the exotic tree Prosopis juliflora. The H' and J' values of the adult trees were H'=1.27 and J9=0.65) and those of the juvenile trees were H'=1.78 and J'=0.75, indicating occupation of the river bank by few species and progenies. From the plants that emerged from the litter+soil, notably herbaceous species, resulted in H'=2.52 and J'=0.66, indicating the invasive impact of P. julliflora, which may be impairing dispersal and germination of seeds of other woody species. The community of adult and regenerating trees on the banks of the Cruz and Espinharas Rivers had low diversity, while shrubs and herbs predominated in the seed bank, and showed few seeds of trees. The diversity indices of the three components (adult and juvenile trees and seed bank) reflect the low richness and distribution of individuals among the species, probably impacted by site invasion by P. juliflora. Measures are needed to ensure the biological diversity of the native arboreal flora on the banks of these rivers and guarantee the continuity of ecological processes and the balance of riverside ecosystems.