Logging plus post-logging thinning may be enough to reduce cutting cycle of some Amazonian tree species

Abstract

This article brings new and refined results useful for the species-specific management in the Amazon Forest. The aim was twofold: (1) to evaluate the medium-term effect of post-logging thinning on the diameter growth of three commercial tree species (Protium apiculatum Swart., Tachigali chrysophylla (Poepp.) Zarucchi & Herend., Minquartia guianensis Aubl.); and (2) to propose species-specific minimum cutting diameters and cutting cycles. The experiment was conducted in the Tapajós National Forest, Brazilian Amazon, where two treatments were implemented: ‘T0’ – unmanaged forest, control; ‘T1’ – managed forest, harvesting of competitor trees with diameter ≥ 45 cm (average reduction of ∼ 30.18 % of the original basal area). Growth models without explicit age were fitted at the tree-species level to project diameter growth. As a result, T. chrysophylla exhibited the fastest growth and the most positive response to ‘T1’. This treatment successfully accelerated the growth rates and boosted the maximum diameter threshold of the three studied species. Extra periodic annual increments provided by ‘T1’ in relation to ‘T0’ varied among species and initial diameter size, reaching the highest value of 0.55 cm year⁻¹ (i.e., 55 cm in 100 years) for M. guianensis. Species-specific minimum cutting diameters varied from 16–32 cm for 'T0' and 23–43 cm for 'T1'. Species-specific cutting cycles varied from 16–35 years for 'T0' and 13–28 years for 'T1', indicating that the generic cutting cycle of 35 years is safe for all species without post-logging thinning, and of 28 years if 'T1' is applied. We concluded that the growth rates vary among species submitted to a same treatment, indicating that the minimum cutting diameter and cutting cycle are sensitive to thinning effects. Our model suggests that the species T. chrysophylla and M. guianensis attain their optimal production volume within the period of 25 years, but this period is insufficient for the species P. apiculatum, although more research is needed to confirm these results in different locations in the Amazon. Our study also demonstrates that wood productivity and sustainability of forest ecosystems in the Amazon can be better linked through a species-specific approach.