Vegetação lenhosa em altitudes no semiárido pernambucano : estrutura, potencial energético e fatores ambientais

Abstract

The Araripe region has suffered one of the greatest environmental impacts of recent years, mainly because it is home to Brazil's plaster center, which uses forest biomass as the main energy source for gypsum conversion. The high demand for this bioenergy has resulted in high anthropogenic pressure on native vegetation, which has been devastated, causing in many areas degraded, desertified and/or in the process of desertification. The problem is aggravated by this region being composed of mountainous areas with varied orographic effects, responsible for the formation of different microhabitats with high biological diversity. The objective of this study was to evaluate floristic and structural diversity of communities and to characterize populations of native woody species with higher values of absolute density (AD) at different altitude levels in the Araripe region of Pernambuco. For data collection the region was stratified into three levels of altitudes: lower (≤ 600 m), middle (600> and <750 m) and higher (> 750 m). Nine fragments were inventoried, three of them per environment. In each fragment, 20 sample units with 250 m² each were distributed, totaling a sample area of 4.5 ha. In the plots the circumferences were measured at the height of the breast of the individuals with inclusion level greater than or equal to 10 cm (CAP 1.30 m ≥ 10 cm), estimated the heights of the individuals, collected environmental information, soil and wood samples woody species with higher AD in the region. Variations of phytosociological parameters, floristic composition, dispersion syndromes, spatial distribution patterns and correlated with geographic and environmental variables were analyzed. The values of moisture, basic density, upper and lower calorific value, estimated, useful calorific value, energy density and wood energy storage with higher DA of the environments were determined. We sampled 6,987 individuals, 10,346 stems, distributed in 35 botanical families, 82 genera and 153 species. The region, at different levels of altitude, presented a diverse floristic-structural composition. At altitudes higher than 750 m, greater species richness was found, with 85. At altitudes of up to 600 m, there are the woody individuals with larger sizes (heights and diameters). In general, the lowland and plateau presented floristic-structural composition with their own characteristics, with few similarities, since the hillside functioning as an ecological ecotone of these two altitudinal strata. The variations of vegetation among altitude strata had as main influencers soil properties and water availability. The burning of freshly cut wood, as is generally practiced in the region, causes a high waste of energy in the ovens. The simple practice of drying the wood in the open air can increase energy efficiency and consequently reduce the amount of wood to be thinned. All the woody species analyzed present woods with high potential for energetic use, as long as they are used partially dry. This work contributes with important information that can be used in the decision making process for the creation of public policies aimed at the conservation and sustainable use of forest resources in the Araripe, Pernambuco region.