Impacts of cuttings on stand and site nutrition, tree growth and stand dynamics on drained peatlands

Thinnings are important also in peatland forest management

The aim of the project was to investigate the impact of intermediate cutting on drained mires. In peatland forests approaching the first thinning stage, trees were often exposed to competition for nutrients and light. At the time of thinning competition was reduced: the needle biomass increased, and the nutritional balance and the growth of the trees improved. The soil's nutritional balance at the growth site was often improved as well.

The timing of the first thinning had a very strong effect on the harvesting economics of peatland forests. The thinning yields with dominant heights less than 13 m were small and harvesting profitability was weak. When the first thinning was postponed until the dominant height of 15-16 m, i.e. the recommended forest marking limit, the wood material yields were doubled. At this point the growth reaction was usually so strong that no significant losses in growth were observed. The growth reaction remained weak only in the most nitrogen-poor peatlands. For a profitable yield throughout the whole rotation period, it seems that it is important to reach a sufficient tree capital before performing major operations in peatland pine stands. If thinning was completely omitted, the situation led to a drastic natural drain and economically weaker results than when following a silvicultural programme containing thinnings.

Additional information on the project: www.metla.fi/hanke/3261/index-en.htm