Carbon dioxide and methane flux measurements from tropical forest soils are scarce. In order to establish reliable global carbon budgets, field measurements of these fluxes from various tropical forest soils under different management practices are critical. These data are also essential for optimizing land-use practices to minimize greenhouse gas (GHG) emissions from forest soils. It is even more critical for countries, such as Bangladesh, that are at the forefront of climate change impacts. In Bangladesh, forests are the only sustainable option within the country to combat climate change. Since the 1980s logging ban, the primary focus of forest management in Bangladesh is to protect forest cover and biodiversity from climate change impacts and maximize climate benefits from forests. Since forest soils are a significant terrestrial carbon sink, enhancing carbon storage in forest soils can be an effective way to mitigate climate change impacts, thus maximizing climate benefits. It is, therefore, crucial to understand the patterns and drivers of forest soil GHG fluxes in Bangladesh and the tropics in general.

Autotrophic and heterotrophic respirations are the primary driver of forest soil CO₂ and CH₄ fluxes. Several biological, chemical, and physical factors affect the relative contribution of autotrophic and heterotrophic respiration on GHG fluxes. Depending on which respiration dominates, forest soils can be either a source or a sink of carbon. However, there is no empirical data from Bangladeshi forest soils on the patterns and drivers of GHG fluxes. For the first time, we report CO₂ and CH₄ fluxes from the Lawachara National Park (LNP), a semievergreen forest and biodiversity hotspot of Bangladesh. In the oldest part of LNP, in winter 2016, we measured CO₂ and CH₄ fluxes from 32 plots (96 locations; collar diameter: 20 cm) using a CS-RC5 soil respiration chamber (CredoSense Inc., Canada) and an ultraportable greenhouse gas analyzer (Los Gatos Research Inc., USA) in a dynamic closed chamber configuration. We simultaneously measured soil temperature, moisture content, pH, ^C⁄N ratio, and available P and collected tree species data.

Our results indicate that soils at the LNP were highly active and showed CO₂ efflux rates comparable to similar tropical forest soils. CO₂ efflux ranged from 1.31 to 12.13 µmol^.m^−2.s⁻¹ with a mean (±SE) value of 4.49±0.19 µmol^.m^−2.s⁻¹. LNP soils were primarily a net CH₄ sink (-2.10±0.10 nmol^.m^−2.s⁻¹). Soil temperature, ^C⁄N ratio, available P, dominant species, and their interactions with soil moisture content and pH were significant predictors of CO₂ effluxes. Soil temperature, pH, and their interactions with moisture content were key drivers of CH₄ fluxes in the study area. Our findings contribute to filling a critical gap in soil C flux measurements in Bangladesh and the tropical forests. Data from this oldest and biodiversity rich national park can be used as a baseline for soil GHG fluxes for Bangladesh. This baseline is critical to determine the impacts of land-use change on soil carbon fluxes. Since there are no measurements of soil GHG fluxes in the country, findings from this study can be used for national C budget estimation, which might be important for getting carbon credits via REDD+.