Derruba direcionada de árvores na Floresta Nacional do Tapajós, Amazônia Oriental: fatores que influenciam e precisão.

Abstract

Since the dissemination of the practices concerning Reduced Impact Logging (RIL) in the 1990s, little research has been conducted to identify the factors that most influence directional felling. Scarce are, as well, the studies aiming to confirm the operational viability of this practice within tropical forest management activities. Thus, more detailed studies involving the variables that influence the execution of directional tree felling are necessary. The objective of the present research was to analyze the variations in tree felling angles and evaluate the contribution of this practice to forest harvesting. The study was conducted in the Tapajós National Forest, municipality of Belterra, state of Pará, Brazilian Amazon. Within an area of 504.30 hectares, a total of 2,102 trees with DBH (diameter at 1.30 m from the ground) ≥ 50 cm were selected for logging, and 1,075 trees (51%), belonging to 17 species considered for the study. The analyses of the variables included 3,225 felling directions associated with the application of directional felling techniques. Nine cutting teams were organized and trained in the technical guidelines of RIL. Team members quantified the time used for planning, cutting, and felling each tree, as well as the angles regarding its natural lean and the planned and effective felling directions. The angular variation between the directional felling procedures was expressed through the absolute differences between the angles of natural lean (QN) and intended felling direction (QP); QP and effective felling direction (QE); and QN and QE. To better understand directional felling, the studied variables were subjected to descriptive statistics and Principal Component Analysis (PCA), a multivariate technique that enables the simultaneous evaluation of several variables. The results of the descriptive statistics indicated that the logged trees predominately fall towards their natural lean or proximate, as evidenced by the correspondence between QN and QP (median = 20 degrees), QP and QE (median = 10 degrees), and QN and QE (median=27 degrees). These results suggest that the directional felling activity in forest harvesting is strongly influenced by the natural lean of the tree. The PCA indicated that the variables diameter, basal area, and stem and branch volumes contributed the most to the variability associated with the directional felling activity. In general, the felled trees did not correlate with the variables cutting time and total time used for directional felling. The analyses suggest that the larger the diameter of a tree, the lower the chance of successfully conducting its directional felling.