Increased carbon stock despite pressure on biomass extraction

Publicerad: 13 november 2020
Enviva wood pellet mill in Sampson County, North Carolina, USA.
Enviva wood pellet mill in Sampson County, North Carolina, USA. Credit: Florian Steierer (UN-ECE/FAO)

Recent EU emphasis on utilizing biological resources to reduce dependence on fossil fuels also adds pressure on extracting biomass. Something that could potentially risk sustainable land management. However, a study into the wood pellet manufacturing in Southeast coastal US that is in compliance with EU recommendations show positive trends in carbon stocks. The carbon stocks have mainly grown in live trees whilst pools of carbon have apparently decreased and there are fewer standing dead trees which, if continued, could affect wildlife and forest diversity.

Environmental and sustainability issues is at the heart of EU policy and recent emphasis on biological resources place greater pressure on utilizing for instance biomass which could end up countering the same environmental goals it seeks to attain. However, US wood pellet production has promoted greater growth in merchantable trees which has led to a larger carbon stock in live trees - which is in compliance with current EU Renewable Energy Directive (EU RED) biofuel trade requirements.

More intensive management behind trends

The study by researchers from SLU, the University of Missouri, and Resources for the Future, performed in procured areas in proximity of wood pellet factories in Southeast coastal US shows a decrease of carbon stock in soil pools. Also, there was a decreasing number of non-merchantable live and growing stock trees but their respective carbon pools remained the same. Such trends are likely driven by more intensive management practices that favor growth in merchantable trees. Some argue that taking out dead biomass prone to ignition could reduce risk of wildfires. However, extracting too much biomass can disrupt nutrient cycles and negatively impact ecosystem structures like wildlife habitat and forest diversity.

Important to continue monitoring

Francisco Aguilar, Professor at the SLU Department of Forest Economics, stresses how new market demand can provide greater levels of carbon stock in live trees but also how more intensive land management practices could negatively impact local forest conditions. - “All-in-all our analysis suggests some positive areas but possible concerns if some trends were to continue. We examined 12 years of data, but that is only a small window of time to assess sustainable forestry. Monitoring using the best-available data shall continue. And it must be observant of other local factors that can significantly alter forest conditions. For instance, systematic assessments must also take into consideration population changes, expansion in wood fibre demand from other competing sectors, and extreme weather.”

The US could contribute up to 60% of the European import demand for wood pellets. At present the trends in carbon stock are positive and complying with EU recommendations. However, discerned negative trends suggest that monitoring should continue to assure sustainability. 

First-of-its-kind systematic assessment

Using the most recently available data from the US Forest Inventory and Analysis Program researchers systematically examined changes in timberland conditions capturing structure (e.g., number of live trees), and reflecting on conditions that can impact wildlife habitat (e.g., number of standing-dead trees) and fluctuations in major carbon pools (e.g., carbon above and belowground in standing live and dead trees, and soils). Systematic changes within procurement areas of the wood pellet industry between 2005 and 2017 took into consideration concurrent anthropogenic (e.g., other industries consuming wood fibres) and naturally-occurring factors (e.g. extreme weather).  Until now, insights into EU RED related policy effects on US forests have been inferred from a review of the extant literature, case studies, and land use projections.