Stump harvesting for bioenergy: A review of climatic and environmental impacts in northern Europe and America

Stump harvesting is defined as an intensification of forest management in comparison with stem-only harvesting and removal of tops and branches. It increases soil mixing and the proportion of bare soil. In contrast to earlier hypotheses, stump harvesting was found to reduce emissions of carbon dioxide (CO2), nitrous oxide, and methane in the short term. In the long term, heterotrophic soil CO2 evolution is reduced. Both model and empirical studies indicate that stump removal can reduce the soil organic carbon (SOC) pool in the short term, but long-term experiments (32-39 years) could not verify any SOC decline. Life cycle assessment studies showed that stumps as fuel resulted in markedly lower emissions of CO2 into the atmosphere, viewed over a whole forest rotation compared to heating by natural gas and coal. Stump removal does not seem to affect timber production in the next forest rotation and often reduces the infection rate of root rot. It increases the natural regeneration of birch and pine, it can increase nitrate leaching at N-rich sites, and it can increase the number of water-filled cavities where methylmercury is formed. Stump extraction decreases the amount of dwarf shrubs in young clear-cuts, but after 1-2 decades, these species are generally recovered. Many species dependent on dead wood are adversely affected by intense stump harvest. Model studies suggest that the risk of species extinction is small when only 10% of the total clear-cut area in the forest landscape is stump harvested, but the risk of extinction rises at increasing extraction intensities. This article is categorized under: Bioenergy > Climate and Environment Energy and Climate > Climate and Environment Energy and Development > Climate and Environment