Partial cutting of peatland forest leads to less carbon dioxide emissions than clear-cutting

Carbon dioxide exchange was measured in a mature, nutrient-rich peatland forest with the eddy covariance (EC) method for 12 years. After the first six years, part of the forest was cut by removing overstory pine trees (70% of the stem volume) while leaving any understory spruces untouched. Meanwhile, the other part of the forest was subjected to clear-cutting, ditch mounding and spruce seedling planting.

Cutting increases carbon dioxide emissions

The study found that before the cuttings, the growing peatland forest was close to zero in terms of its carbon balance, as the growing trees bound as much carbon as the forest floor released. After the cuttings, the forest became a source of carbon dioxide. However, these emissions were significantly smaller in the area that was subjected to partial cutting rather than clear-cutting. This was because the partially cut area contained significant quantities of trees and other vegetation that could absorb the carbon dioxide from the atmosphere.

The partially cut area turned into a carbon dioxide sink four years after it was cut. Ultimately, it became such an effective sink that it nullified its carbon dioxide emissions for the first three years, and its combined six-year carbon dioxide balance did not differ significantly from its pre-cutting balance. The clear-cut area, on the other hand, remained a relatively large carbon dioxide source throughout the six-year measurement period, even though its emissions decreased year by year.

According to the study, cutting a peatland forest only partially can help significantly reduce its post-cutting carbon dioxide emissions, if the forest has a vibrant understory. It is important to note, however, that trees only function as a temporary carbon storage. Most of the carbon in a peatland is preserved in its peat, which is accumulated over many millennia. The decomposition of peat is caused by drainage, and this decomposition process cannot be halted with any specific forest cultivation method as long as the peatland itself remains drained.

The study is exceptional, as it is the first of its kind to continuously measure the carbon dioxide exchange between a drained peatland forest and the atmosphere with the EC method for such a long period of time, and in a way where the time series covers the periods before and after the cutting.

Further information:

Annalea Lohila, Research Professor, Finnish Meteorological Institute, University of Helsinki, annalea.lohila@fmi.fi

Paavo Ojanen, Researcher, University of Helsinki, Natural Resources Institute Finland (Luke), paavo.ojanen@helsinki.fi

Mika Korkiakoski, Researcher, Finnish Meteorological Institute, mika.korkiakoski@fmi.fi

Scientific article is available on Agricultural and Forest Meteorology.

Reference: Korkiakoski, M., Ojanen, P., Tuovinen, J.-P., Minkkinen, K., Nevalainen, O., Penttilä, T., Aurela, M., Laurila, T., and Lohila, A.: Partial cutting of a boreal nutrient-rich peatland forest causes radically less short-term on-site CO2 emissions than clear-cutting, Agric For Meteorol, 332, 109361, https://doi.org/10.1016/j.agrformet.2023.109361, 2023.