Avaliação do papel das árvores grandes para o manejo florestal sustentável

Abstract

Large trees (DBH ≥ 60 cm) contribute to forest structure and dynamics, play key ecological roles in ecosystem functioning, and usually account for most of the commercial timber harvested during selective logging. This study investigated the ecological contributions of large trees in a dense ombrophilous forest selectively logged 23 years ago in the state of Amazonas, Brazil, focusing on their influence on timber production, biomass stocks, and ecosystem structure. We evaluated 41 permanent plots distributed across three logging units (UPAs), harvested in consecutive years (1996, 1997, and 1998). Paired t-tests revealed that, prior to logging, large trees corresponded to slightly more than one quarter of the forest’s total volume and biomass stocks (29,2% and 27,6%, respectively). By the time of the timber harvesting, large trees represented on average 85% of the commercial volume extracted. During the recovery time, large trees also contributed to forest growth, accounting for 23% of the mean annual periodic increment of all individuals. Their contribution to mortality was lower, about 7,5% of the total. Overall forest mortality averaged 7,6 (±2,3) trees ha⁻¹ yr⁻¹, while recruitment averaged 4,8 (±0.5) trees ha⁻¹ yr⁻¹. By the end of the recovery period, before the second cutting cycle, large trees played a prominent role in forest recovery: they restored, on average, 76,4% of the commercial volume stock harvested in the first cycle (based on the original species list), and in the last census they represented 76,2% of the commercial volume stock (considering the expanded list of commercial species across UPAs). Twenty-three years after logging, the forest had recovered 95,5% of its pre-harvesting total volume stock and 96,5% of its aboveground biomass, while the commercial volume stock available for the second cutting cycle reached about 76,2% of pre-logging levels, corresponding to 51,54 (±13,3) m³ ha⁻¹, of which large trees accounted for 70%. In a hypothetical immediate second harvest, this stock could be reduced by almost half (46,7%). Beyond their importance in the managed forest structure, rapid individual field assessments of 39 large trees across five permanent plots in UPAs B and D recorded ecological attributes, highlighting their functions in canopy light input, provision of food and shelter for fauna, and dominance in the forest canopy.