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

Abstract

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 (CO 2 ), nitrous oxide, and methane in the short term. In the long term, heterotrophic soil CO 2 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 CO 2 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 clearcuts, 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.

Experimental evidence on biodiversity impacts of variable retention forestry, prescribed burning, and deadwood manipulation in Fennoscandia

“…This practice impacts saproxylic beetles negatively through a loss of substrates (Victorsson and Jonsell 2014;Work et al 2016;Ranlund and Victorsson 2018) and through functioning as ecological traps: piles of residue and stumps-with beetles in them-are eventually moved from forest to power plants (Hedin et al 2008;Victorsson and Jonsell 2013). A modeling study suggests that the risk of extinction of these species may be small if only 10% of the total clear-cut area in a forested landscape is stump harvested, but the risk rises with increasing intensity of extraction (Persson and Egnell 2018). Harvesting of stumps and residuals also impacts, e.g., epiphytic and epixylic species through exposing mineral soil and destroying CWD; lichens are more severely impacted by slash removal than by stump removal (Hiron et al 2017).…”

Soil changes and long-term ecosystem recovery from physical and chemical load – stump harvesting and sprinkling infiltration as case studies

“…Whether stump harvesting affects stand productivity is under debate. In Finland, stump harvesting started in 2000 and peaked in 2010-2013 with 1.1 million m 3 annually, the current annual harvest being 0.76 million m 3 (LUKE, 2017; Persson and Egnell, 2018). Stump harvesting is currently only practiced in fertile and moderately fertile Norway spruce (Picea abies (L.) Karst.)…”

A Spatially Explicit Decision Support System for Assessment of Tree Stump Harvest Using Biodiversity and Economic Criteria

“…A continually growing demand for alternative renewable energy sources [1] has resulted in increased harvest of forest-based bioenergy (heat, electricity or transportation fuels) products in the Nordic and Baltic countries [2][3][4]. Primary forest residues from logging, in the form of slash (tops, branches and twigs) and tree stumps constitute major sources of forest-based bioenergy products [2,3]. Slash is currently extracted for bioenergy production in Sweden, whilst stumps have been under evaluation as a potentially significant future source of bioenergy.…”

“…Increasing harvest of stumps implies more intensive use of forests, raising issues of environmental sustainability [19,21,22] and social acceptance [23]. The harvesting of stumps may affect the ecological state of the forest stand both in the short and long term [3,18,19]. In Sweden, the Governments environmental quality objective "Reduced Climate Impact" must be achieved in such a way and at such a pace that biological diversity and forest sustainability are not jeopardized according to other objectives of "A Rich Diversity of Plant and Animal Life" and "Sustainable Forests" (www.miljomal.se).…”

“…Stumps are more abundant in managed than unmanaged forests, and are especially important to consider in managed forests where they constitute a large part of the total coarse deadwood volume and are used by many deadwood-dependent organisms [30]. There is a growing bulk of North European research that seeks to evaluate the role of stumps as habitats for deadwood affiliate biodiversity [3,28,[31][32][33]. This opens up new opportunities to synthesize current knowledge on stump affiliate biodiversity in analytical and spatially explicit DSSs that integrate both biodiversity and production objectives for stump harvesting.…”