Produção de biomassa em área de Caatinga manejada sob efeitos do tempo decorrido pós corte e de variáveis climáticas

Abstract

The Caatinga biome is characterized by a wide diversity of woody species that can be used as an energy source. However, in most cases, the exploitation of forest timber resources in this biome has been carried out in the absence of scientific responses that can guide the ideal and truly sustainable way to access this renewable resource, considering the regeneration dynamics after cutting and site conditions. The objective of this study was to evaluate the influences of post-cutting age and climatic variables on biomass production in a Caatinga area under sustainable forest management. The study was conducted in the Margarida Complex, which includes the Quimporó and Estrela do Norte farms, located in the municipality of Cruzeta/RN, Brazil. Sixty-five 20 x 20m (400m²) temporary plots were allocated in seven compartments, which are part of the local sustainable forest management plan, covering a total area of 26 ha. In these plots, measurements of diameter at the base and at breast height, as well as total height of each individual in the inventory, were made according to the Caatinga Management Network requirements. The initial results generated the phytosociological structure of the stands, which allowed the calculation of the importance value index for each species in the study areas. Based on the results of the woody biomass quantity, the dry mass of wood was determined, considering the moisture content previously estimated. To analyze the influences of post-cutting time and climatic variables, compartments exploited at different times and a database composed of precipitation, maximum and minimum temperatures, evaporation, evapotranspiration, and humidity were used. Statistical analysis was performed using a non-linear sigmoidal regression model (logistic model). The results indicated that postcutting time influences wood formation for the evaluated local conditions. Biomass varied with post-cutting regeneration times, with the highest value observed in the 13-year-old compartment (22.65 Mg/ha) and the lowest in the most recent 7-year-old compartment (11.38 Mg/ha). Wood production did not show a linear increase with compartment age, suggesting the influence of other factors on wood regeneration dynamics. The rate of recovery of woody vegetation varied from 37% to 87% between 7 and 14 years, respectively. Analyses of wood production and forecasts of Annual Mean Increment, Annual Periodic Increment, and climatic variables showed a positive correlation with post-cutting age and average annual precipitation. On the other hand, biomass production showed a negative correlation with Annual Mean Increment and Annual Periodic Increment in relation to maximum temperature, average temperature, and evapotranspiration.