Degradation increases peat greenhouse gas emissions in undrained tropical peat swamp forests

Abstract

Tropical peat swamp degradation can modify net peat greenhouse gas (GHG) emissions even without drainage. However, current Intergovernmental Panel on Climate Change (IPCC) guidelines do not provide default emission factors (EF) for anthropogenically-degraded undrained organic soils. We reviewed published field measurements of peat GHG fluxes in undrained undegraded and degraded peat swamp forests in Southeast Asia (SEA) and Latin America and the Caribbean (LAC). Degradation without drainage shifted the peat from a net CO2 sink to a source in both SEA (− 2.9 ± 1.8 to 4.1 ± 2.0 Mg CO2–C ha−1 yr−1) and LAC (− 4.3 ± 1.8 to 1.4 ± 2.2 Mg CO2–C ha−1 yr−1). It raised peat CH4 emissions (kg C ha−1 yr−1) in SEA (22.1 ± 13.6 to 32.7 ± 7.8) but decreased them in LAC (218.3 ± 54.2 to 165.0 ± 4.5). Degradation increased peat N2O emissions (kg N ha−1 yr−1) in SEA forests (0.9 ± 0.5 to 4.8 ± 2.3) (limited N2O data). It shifted peat from a net GHG sink to a source in SEA (− 7.9 ± 6.9 to 20.7 ± 7.4 Mg CO2-equivalent ha−1 yr−1) and increased peat GHG emissions in LAC (9.8 ± 9.0 to 24.3 ± 8.2 Mg CO2-equivalent ha−1 yr−1). The large observed increase in net peat GHG emissions in undrained degraded forests compared to undegraded conditions calls for their inclusion as a new class in the IPCC guidelines. As current default IPCC EF for tropical organic soils are based only on data collected in SEA ombrotrophic peatlands, expanded geographic representation and refinement of peat GHG EF by nutrient status are also needed.

Quantifying the fluxes of carbon loss from an undrained tropical peatland ecosystem in Indonesia

“…Estimating onsite peat CO 2 emissions following IPCC guidelines requires values for both carbon loss via heterotrophic respiration and the carbon input from litterfall and root mortality. Applying literature values for carbon inputs and soil respiration partitioning ratios specific to peatlands in Southeast Asia 38 , we estimate that the peat onsite CO 2 budget for the PPSF is − 25.1 ± 7.5 MgCO 2 e ha −1 yr −1 and for the SPSF is – 22.0 ± 5.6 MgCO 2 e ha −1 yr −1 (Table 5 ). These estimates for the potential onsite CO 2 sink for the PPSF and SPSF are much larger than those reported for undegraded and degraded undrained peatlands in Southeast Asia 38 .…”

“…Applying literature values for carbon inputs and soil respiration partitioning ratios specific to peatlands in Southeast Asia 38 , we estimate that the peat onsite CO 2 budget for the PPSF is − 25.1 ± 7.5 MgCO 2 e ha −1 yr −1 and for the SPSF is – 22.0 ± 5.6 MgCO 2 e ha −1 yr −1 (Table 5 ). These estimates for the potential onsite CO 2 sink for the PPSF and SPSF are much larger than those reported for undegraded and degraded undrained peatlands in Southeast Asia 38 . Our higher estimates for the onsite CO 2 sink potential may be due to the lower estimated heterotrophic respiration rates at Muara Siran compared to other undrained peatlands.…”

Editorial: Peatlands for climate change mitigation in agriculture

“…In addition to active drainage of tropical swamp forests and subsequent land use change, peatland degradation due to unsustainable harvesting of e.g., Mauritia flexuosa palms for fruit, affects site hydrology and GHG fluxes. A site study for a peat swamp forest in Peru ) and a review of published field measurements by Swails et al (2024) for sites in Southeast Asia, Latin America and the Caribbean provide initial insights into the magnitude of GHG flux changes due to degradation. Swails et al (2024) conclude that "the large observed increases in net CO 2 emissions in undrained degraded forests compared to undegraded conditions calls for their inclusion as a new class in the IPCC guidelines" and that either protection or a new approach to sustainable management of swamp peatlands is needed to limit the impact of tropical peatland degradation on GHG emissions and the climate.…”