When big trees fall: Damage and carbon export by reduced impact logging in southern Amazonia

Abstract

We examined carbon export in whole logs and carbon accumulation as coarse woody debris (CWD) produced from forest damage during all phases of the first and second year of a certified reduced impact logging (RIL) timber harvest in southern Amazonia. Our measurements included a 100% survey of roads and log decks, assessment of canopy damage and ground disturbance in skid trails and tree-fall gaps, and measurement of carbon exported from the site in logs. Log deck and road construction crushed one and five trees in the 10–60 cm diameter at breast height (DBH) class per hectare logged, disturbed areas of 24 and 100 m 2 ha −1, respectively, and together disturbed about 1% of the forest. On average 1.1–2.6 trees ha −1 were harvested over the two years. Logged gaps constituted the greatest disturbance on an area basis (4–10% of the forest) and CWD generation (1.9–4.4 Mg ha −1 logged). In gaps, felled trees severed or crushed 10 trees ≥10 cm DBH per tree logged, which corresponded to 1.7 Mg ha −1 of CWD per tree logged. Crown height – measured from the first bifurcation to the top of the crown – rather than tree height was the better predictor of gap size formed from tree felling ( R 2 = 0.41). Logging activities significantly reduced leaf area in roads, log decks and gaps, with the greatest reduction (48%) in log decks and least in logged gaps and roads (28–33%) compared to undisturbed forest. A total of 37 species were harvested, with 36% of the total trees harvested and 48% of the total carbon exported from the site in three of the most common species. Logging damage produced 4.9–8.8 Mg C ha −1 logged of CWD from all phases of the operation. Carbon export in whole logs (2.1–3.7 Mg C ha −1 logged) represented 1–3% of the total standing forest carbon ≥10 cm DBH (138 Mg C ha −1). The mean carbon ratio (per hectare logged) of C in CWD to C exported in logs was 2.4. The disturbance, damage, carbon export and CWD data we present advances understanding of the effect of selective logging on tropical forest dynamics of the Amazon Basin. Our results indicate that certified timber harvest in Amazonia under RIL is a viable forest management option to reduce damage and CWD production compared to conventional logging (CL) practices; however, the benefits of disturbance reduction from RIL relative to CL are only realized at greater volumes of timber extraction.