Production of greenhouse gases by logging residue in boreal clear-cut forests

Forest deadwood is an important carbon reserve, estimated to contain 8% of the total forest carbon. This type of woody debris is recognized as a source of carbon dioxide (CO₂), as the carbon is released back into the atmosphere by microbial decomposition. Production of methane (CH₄) and nitrous oxide (N₂O) has also been reported. In managed forests, logging residues form a major source of fine deadwood, but its role in the greenhouse gas exchange of forest ecosystems is poorly understood. We studied the greenhouse gas production of spruce and birch left-over fine woody debris and estimated the residence time of these residues at 18 spruce-dominated boreal forest sites in Central Finland. The study areas consisted of clear-cut forest stands, totally covering approximately 47 hectares, with logging residue ages varying between 0 and 10 years. The research was carried out over eight months from May to December 2019. We observed that CO₂ dominated the greenhouse gas production of the logging residues, with the production being regulated by air temperature, tree species, residue age, and wood moisture. Emission of CO₂ continued throughout the research period with a clear seasonal pattern. Production of CH₄ and N₂O was also observed, but not in climatically-relevant amounts. Deadwood half-life was estimated at 18 years for spruce and 9 years for birch. Our study demonstrates that logging residues form a mid-term carbon reserve and suggests that global warming could reduce the lifetime of the residues as a result of elevated and temperature-dependent CO₂ release in the studied Myrtillus type forest stands.