Dinâmica e estrutura de espécies arbóreas após a exploração madeireira na floresta nacional do Tapajós

Abstract

Whereas forests are dynamic biological systems that are in continuous change is necessary to understand the forest and its role in ecosystem functioning in search of a better strategy both for conservation and for the use of their forest resources. Thus, this study aimed to evaluate the dynamics and structure of a forest operated under different cutting intensities to 31 years in eastern Amazonia, estimate for the next cutting cycle. The experiment is located in the Tapajós National Forest, the city of Belterra, along of 67 km of Highway Santarém-Cuiabá, state of Pará. The following treatments were tested: T0 - control, represented by the undisturbed forest; T1 - cutting commercial trees with dbh ≥ 45 cm; T2 - cutting commercial trees dbh ≥ 55 cm. In each treatment were installed 18 permanent plots of 0.25 hectares and observed all trees with DBH greater than or equal to 5 cm. The logging occurred in 1979. The first monitoring was conducted in 1981 and the last in 2012. For treatments analyzed except for the control, the number of species has increased. Recruitment rates were higher than mortality rates in treatments explored ranging from 3.30% to 3.78% for the recruitment and 2.60% to 2.94% mortality, respectively T1 and T2. The basal area and volume showed progressive growth. At the end of monitoring the basal areas found were 27.5, 30, 28.6 and m².ha-1 and volume were 225.6, 267.3, 258.8 m³.ha-1, to respectively T0, T1 and T2. The average increase in volume of all species were 7.76 ± 1,33 m³.ha-1.yr-1 and 8.58 ± 1,32 m³.ha-1.yr-1 (IC 95%), and commercial species were 3.22 ± 0.60 m³.ha-1.yr-1 and 3.36 ± 0.47 m³.ha-1.yr-1 (IC 95%), respectively to T1 and T2. The intensity of the treatments was not satisfactory to keep the original floristic composition of the forest. On the other aspect, the operation provided the recovery of individuals and favored the growth of the remaining individuals. Growth and volume of the 1979 experimental forest management were not sustainable, but the present forest structure suggests that a second cutting cycle.