Sucessão secundária em áreas de Mata Atlântica de Pernambuco : mudanças florísticas e estruturais

Abstract

Secondary forests have been considered as priority areas for conservation in tropical regions due to their possible role as buffer zones. They serve as habitats for plants and animals coming from destroyed mature forests and as corridors between forest fragments. They also have the capacity to accumulate biomass and nutrients at high rates, to maintain biogeochemical cycles and to preserve soil and water at levels similar to those of mature forests. Along the successional process, secondary forests show tendencies of lower density, higher biomass, height, diameters,richness and diversity and changes in floristic composition and biological forms. In Pernambuco,large abandoned areas, mainly from sugarcane plantations, resulted in forest fragments at different successional stages, with largely unknown biological characteristics. This work, divided into two manuscripts, aimed at characterizing the flora according to the biological form (trees, shrubs, herbs, epiphytes, vines) and the structure, richness and diversity of woody species in six regenerating forest fragments, 12 and 20 years old, established at sites previously planted to sugarcane, at Igarassu municipality, Pernambuco state. The regenerating fragments were chosen based on aerial photos taken in the 60´, 70´and 80´, satellite images captured in 2005 and interviews with local residents. In the three 12 year old fragments, 136 species, belonging to 50 families, were identified, while in the 20 year old fragments there were 161 species, belonging to 57 families, an increase equivalent to 15% in the species richness. There were no significant differences between 12 and 20 year old fragments, in the flora distribution among biological forms. However, the species compositions were different, mainly those of herbs and shrubs. Thenumber of species in the tree flora increased with the age of the fragment as well as their floristic similarity (SØrensen index = 0.41). The older regenerating fragments were more similar to mature forests. In the similarity matrix with 211 species, 53% occurred only in the regenerating fragments and were not registered in the survey of two mature forests in the same property but some of them are included in the general species list of mature forests of the property. The first manuscript concludes that the species in the regenerating fragments constitute a subset of the flora of the nearby mature forests. The second manuscript indicates that there was a tendency of lower canopy tree density than in the mature forests, in spite of the absence of significant differences between the fragments of different ages. This confirms the usual pattern for tropical forests. Height, diameter, branch numbers, richness and diversity of the canopy trees were higher in the older fragments while, for the undercanopy plants only density and richness were different. Basal areas were not different. Distributions into diameter and height classes indicated that the most important species changed along the successional process. Canonic correlation analysis suggested that plant density was correlated to soil texture. In general, comparing with mature forests, results corroborate the successional patterns reported by several authors for tropical forests, with a faster recovery of richness and structure than floristic composition.