Long-term effect of different forest thinning intensity on carbon sequestration rates and potential uses in climate change mitigation actions

Recent model projections and many research results along the world suggest that forests could be significant carbon sinks or sources in the future, contributing in such a way to global warming mitigation. Conversion of coppice forest to high forest may play an important role towards this direction. However, the most effective way for this to succeed is questionable. This study examines the long-term effect of different intensity thinning (light 10% of the volume removal every 5–10 years, moderate 15%, and heavy 20%) on biomass, and on all the carbon pool categories (according to IPCC), as well as the accumulation rates, in a 77-year-old oak ecosystem, which has been subjected to conversion from coppice to high forest through repeating thinning since 1973. The research included numerous field tree measurements, and a systematic sampling of standing and fallen dead wood, litter, and surface soil up to 50 cm depth. Data analysis shows that heavy and moderate thinning result in a greater accumulation of carbon in the aboveground ecosystem pools, especially in living biomass, with an average annual rate of 1.62 Mg C ha−1 carbon accumulation in living aboveground tree biomass, resulting in a carbon pool of 125.04Mg C ha−1 at the age of 77 years. Dead wood volume was found low in all thinning treatment with significant differences between the thinning intensities. Litter carbon pool was also affected by moderate and heavy thinning, while soil carbon was unaffected by the treatments. The findings could contribute on climate change mitigation actions if they are adopted in forest management plans of similar types of forest ecosystems; a periodical thinning application of removal ca. 20% of wood volume is suggested.