Partial cutting of a boreal nutrient-rich peatland forest causes radically less short-term on-site CO2 emissions than clear-cutting

Abstract

Wide-spread harvesting of forests growing on drained peatlands is foreseen to take place in Finland in the near future. A hot question is if continuous cover forestry utilizing partial cuttings could be used to mitigate carbon dioxide (CO2) emissions and the consequent climatic impact compared to traditional clear-cutting and even-aged forest management. To assess the impact of clear-cutting vs. partial cutting, we first measured CO2 exchange with the eddy covariance (EC) method for six years in a mature, nutrient-rich peatland forest in southern Finland. Part of the forest was then partially cut (74% of the stem volume), and part of it was clear-cut, and CO2 exchange of both areas was measured for another six years. Tree growth was recorded before and after the cuttings to separate the contributions of tree stand and forest floor to CO2 exchange. Before the cuttings, the site had an annual CO2 exchange close to zero, but both cutting methods turned it into a CO2 source. However, the first-year emissions from the partial cutting area (800 g CO2 m−2 yr−1) were markedly lower than the emissions after clear-cutting (3100 g CO2 m−2 yr−1). The partial cutting area remained a CO2 source during the first three years but turned into a CO2 sink after that, while the clear-cut area acted as a large, although diminishing, CO2 source for the whole measurement period. The total six-year CO2 balances before and after partial cutting did not differ significantly, while the emissions after clear-cutting were on average 2240 g CO2 m−2 yr−1 larger than before it. Combining the EC data with the tree growth measurements showed that the forest floor was losing C both before and after harvestings. In conclusion, partial cutting resulted in clearly smaller CO2 emissions than clear-cutting at least in the short term.