No abstract

Selective logging is among the main causes of tropical forest degradation, but little is known about its effects on greenhouse gas (GHG) fluxes from highly weathered Ferralsol soils in Africa. We measured soil CO2, N2O, and CH4 fluxes, and their soil controlling factors at two forests that had undergone conventional selective logging and reduced-impact logging in Cameroon. Each logging system had four replicate plots, each included the disturbed strata (road, logging deck, skidding trail, and felling gap) and an undisturbed reference area. Measurements were conducted monthly from September 2016 to October 2017. Annual GHG fluxes ranged from 4.9 to 18.6 Mg CO2–C, from 1.5 to 79 kg N2O–N, and from − 4.3 to 71.1 kg CH4–C ha−1 year−1. Compared to undisturbed areas, soil CO2 emissions were reduced and soil CH4 emissions increased in skidding trails, logging decks and roads (P < 0.01) whereas soil N2O emissions increased in skidding trails (P = 0.03–0.05). The combined disturbed strata had 28% decrease in soil CO2 emissions, 83% increase in soil N2O emissions, and seven times higher soil CH4 emissions compared to undisturbed area (P ≤ 0.01). However, the disturbed strata represented only 4–5% of the area impacted in both logging systems, which reduced considerably the changes in soil GHG fluxes at the landscape level. Across all strata, soil GHG fluxes were regulated by soil bulk density and water-filled pore space, indicating the influence of soil aeration and gas diffusion, and by soil organic carbon and nitrogen, suggesting the control of substrate availability on microbial processes of these GHG.

Forest CO 2 dynamics feature prominently in global carbon (C) cycle studies, but the role of forests in the CH 4 cycle is relatively poorly understood. Although a considerable number of studies have been undertaken to constrain the net balance of CH 4 , the global CH 4 budget is still characterized by high uncertainty (Saunois et al., 2020), especially for the tropics (Valentini et al., 2014). Until now, bottom-up estimates of the global CH 4 budget from terrestrial ecosystems do not distinctively include an estimation of the contribution of tree stem CH 4 flux (Kirschke et al., 2013;Saunois et al., 2020), despite emerging evidence pointing to significant tree stem CH 4 emissions from wetland and upland ecosystems (Barba, Bradford, et al., 2019;Covey & Megonigal, 2019). Consequently, this contributes to the widely differing CH 4 estimates from emission-based, bottom-up models and estimates obtained from top-down modeling approaches, highlighting the considerable uncertainty regarding the relative contributions of regional sources and sinks of CH 4 (IPCC, 2013).