Variação interanual do componente herbáceo em áreas de caatinga preservada e manejada no sertão pernambucano

Abstract

The human impacts are indicated in the literature as causative agents of change in vegetation structure, especially in dry areas. Caatinga, xerophytic vegetation predominant Brazilian semiarid, few studies of the interactions that occur between layers of vegetation and with these environmental changes, natural or manmade, that are determining the replies submitted by them. Thus, this study was conducted at the Experimental Field Caatinga Embrapa Semiárido and was divided into two chapters, the first seeking to study the interannual variations in the composition and abundance of herbaceous assembly areas preserved and anthropogenic, and second that aimed assess the role of isolated trees in diversity and abundance of herbs. The floristic-structural first chapter occurred during the rainy season (January-May), in the years 2010 and 2011 at two locations with different levels of conservation of vegetation, called the preserved and managed area. In each area were demarcated two 10x40m plots were allocated where 50 sub-plots of 1x1m, totaling 100 sub-sample plots in each area, totaling 200 sub-plots sampled. Differences were observed in the indices of diversity by Hutcheson's t test and the similarity was evaluated by a non-metric multidimensional scaling based on Bray-Curtis coefficient. To assess differences in density and richness between areas was used an analysis of variance for repeated measures (ANOVA). The significance of density and average wealth between areas and between years were assessed by the Tukey test. The results show high floristic similarity occur between areas, but the ordination analysis found differences and significant correlation between areas. Between years, differences and analyzes showed a significant correlation only in the managed area. Analysis of variance showed that the conservation status of the areas explains the variations in wealth in both years. The Tukey test detected significant differences in the values of average wealth between areas, but between years, regardless of the variation in total rainfall, the values did not vary significantly. The diversity differed significantly between areas and between years, being higher in the managed area. The study was conducted in the second chapter in the rainy season of 2011. For the same 15 individuals were selected tree species Spondias tuberosa Arruda, distributed in three habitats of the experimental field, with five individuals in the young forest, mature forest five in and five in the Active Germplasm Bank of S. tuberosa. In each habitat were chosen two locations, one below the canopy of S. tuberosa (shading) and the other in full sun. At each site were allocated three plots of 1x1m. In total 90 plots were demarcated, 30 in each habitat, with 15 plots shaded and unshaded 15 plots. Differences in structural attributes of the assembly of herbaceous between areas and between shade conditions of each area were verified by standardized test average wealth in Generalized Linear Model (GLM) ANOVA nested. Differences in density and richness averages were verified by Tukey test (p <0.05). The plots under direct incidence of sunlight on BAG and mature forest showed significantly lower wealth. In young forest no significant difference between the shading conditions. The highest density values were recorded in the plots BAG and full sun. The results of this study demonstrate that the management of the area contributed to changes in the composition, but the variations in total rainfall between years did not influence the wealth and size of the populations of herbaceous and that the maintenance of isolated trees positively influenced species richness values but the establishment of herbaceous species is favored in areas exposed to sunlight.