Wetlands are important for climate as long term carbon storages. The wetland vegetation removes carbon dioxide from atmosphere and the carbon is accumulated in the soil as peat. However, they are also sources of methane, an important greenhouse gas. Lowering the soil water table enhances peat decomposition and induces large carbon dioxide emissions and loss of accumulated peat, but also reduces methane emissions as a secondary effect. Alfawetlands WP4 studies these trade-offs and the impact of management on the peatland GHG exchange and C storages in living labs by using ecosystem modelling. In a new study led by Finnish Meteorological Institute (Tyystjärvi et al., 2024), researchers explore how different forest management practices, peatland ecological restoration, and climate change scenarios might alter methane emissions in forestry-drained peatlands across Finland. They focused on three primary management practices:
- Rotational Forestry: A traditional approach where forests are clear-cut and then allowed to regrow. This method requires maintaining ditches to control the water table level.
- Continuous Cover Forestry: An alternative to rotational forestry, where only part of the forest is harvested, maintaining a more continuous forest canopy and higher water table level.
- Peatland Ecological Restoration: Returning drained peatlands to wetlands by rewetting them, often by blocking drainage ditches and reducing tree cover.
They also compared the model results to measurements across Finland. To predict how these practices and climate scenarios might affect future methane emissions, the researchers used ecosystem modelling: The simulations ran through the 21st century to track changes in methane fluxes, soil water table level, soil temperatures, and soil carbon dynamics.
Figure 1: Ecosystem model schematics
Figure 2: Drained peatland forest in Rottasniitunsuo, where ecological restoration takes place in 2024
Key Findings
The study found several important trends: Management practices significantly influenced peatland water table levels and methane emissions. Ecological restoration led to increased methane emissions, while clearcutting caused a temporary spike in emissions. Continuous cover forestry had more moderate impact on emissions compared to rotational forestry. Over the century, restored peatlands showed a gradual decrease in methane emissions following the decomposition of harvest residue. Decomposition was stronger in southern Finland. In contrast, drained peatland forests saw occasional methane emissions becoming more common as water table levels and soil temperatures rose. This effect was stronger in Northern Finland.
The study underscores the complex interactions between peatland management practices, climate change, and methane emissions. It highlights that while ecological restoration can initially increase methane emissions, it may ultimately lead to reduced emissions over time. The magnitude of these changes varies across boreal region. Understanding these trends is crucial for developing sustainable peatland management practices that maintain carbon accumulation in the soil and minimise the greenhouse gas emissions. The studies at ALFAwetlands Living Labs and upscaling for the regional assessment is continued with focus on both carbon dioxide and methane fluxes and soil carbon storages.
Sources:
Tyystjärvi et al., Biogeosciences Discussions, https://doi.org/10.5194/egusphere-2023-3037, 2024
Main photo: Clearcut and GHG flux measurements by Finnish Meteorological Institute in Lettosuo drained peatland forest