Effects of sustainable forest management on tree diversity, timber volumes, and carbon stocks in an ecotone forest in the northern Brazilian Amazon

Abstract

The tension between the large global demand for tropical timber, and ecological sustainability and local socioeconomic development in the fragile natural ecosystems of the Amazon region has challenged many generations. In this case study, carried out in an ecotone forest in the northern Brazilian Amazon, we seek to demonstrate how forest management can became more sustainable through silvicultural prescriptions that reduce forest degradation and soil erosion. We evaluated the effects of the sustainable forest management (SFM) on tree diversity, timber volumes, and carbon stocks. A continuous forest inventory was carried out in nine 1-ha permanent plots (900 subplots of 100 m²), distributed in three treatments with three repetitions: T1 = control without selective logging, T2 = SFM, and T3 = SFM + silvicultural treatment of thinning release by tree girdling and poisoning. SFM was carried out with an average of three commercial timber trees harvested per hectare with DBH (diameter at breast height) ≥ 50 cm, corresponding to a timber volume of 20 ± 6 m3 ha-1, equivalent to the removal of 7 ± 2 Mg C ha-1 (5% of the original C). The formation of clearings (gaps) arising from the falling of exploited trees (0.12 ± 0.09 ha) resulted in greater impacts on the forest structure than the construction of 4 m skidder trails (0.06 ± 0.04 ha), with an average of 7 ± 4 damaged trees ha-1 and 5 ± 3 dead trees ha-1. Although six trees species became locally extinct, tree diversity was little altered, and timber volumes and forest carbon volume stocks remained essentially constant at this average logging intensity. Based on our results, sustainable forest management can become an efficient model for land use in the Amazon when harvesting is carried out using this average logging intensity. However, long-term monitoring studies using permanent plots in ecotone forests in the Brazilian Amazon will still be necessary. Quantifying, evaluating, and reporting impacts related to forest management will enable the formation of an empirical basis to support sustanaible forestry practices and for updating environmental legislation, contributing to local socioeconomic development, and maintaining the environmental services provided globally by tropical forests. © 2022