Long-lived wood products of improved birch bring more climate benefits

Increasing the diversity of forest tree species in Swedish forests can contribute to mitigating the effects of climate change. Fast-growing broadleaves, such as genetically improved birch which is already adapted to Swedish conditions, can contribute to both more diverse and resilient forests as well as higher production value.

In a new study Aureo Aparecido Abreu Junior, PhD student at SLU and within Trees For Me, and his research colleagues have calculated biogenic carbon dynamics in the living tree biomass and soil, the carbon stored in wood products, greenhouse gas emissions from different value chains, and potential substitution effects from replacing high greenhouse gas emission materials with wood products. The climate effects from using genetically improved and planted birch have been compared with naturally regenerated birch, and the climate impact of different wood products has also been assessed. The estimation of the impact has been based on a fixed 50-year rotation period at the stand level.

Long-lived products and genetic improvement

According to the study, it brings more climate benefits both to use birch for more long-lived products and to improve birch to grow faster. When compared, the effects of changing to long-lived products were found to be as great as the effects of planting and using improved birch instead of naturally regenerated. Using improved birch thus contributes more to climate benefits than naturally regenerated. The latter is currently more common in Swedish forests and primarily used for pulp and bioenergy.

“If we could combine the strategies of using improved birch in long-lived wood products, the climate benefits would be the most beneficial”, says Aureo Aparecido Abreu Junior.

The Intergovernmental Panel on Climate Change (IPCC) has provided guidelines on the definition of long-lived products from harvested wood that store carbon for extended periods. Default values have been identified for the products’ expected “half-lives” to estimate the time carbon is stored in different wood products.  The "half-life" indicates that after this period, half of the carbon in that product category is assumed to have been released back into the atmosphere. The remaining carbon can be stored for longer periods, with some products remaining in use for much longer than the half-life. Long-lived wood products include e.g. sawnwood (35 years of expected half-life) and wood-based panels (25 years). If the material can be reused in other products, the climate benefit is even greater (so-called cascade use).

Challenges and opportunities for forest sector

Developing improved birch genotypes which bring higher volume gain and better wood quality is needed for the industry to be able to deliver long-lived wood products.

“Harvesting sawlogs from non-improved birch stands is a great challenge today because most of them have crooked stems and do not have the required diameter for processing in the sawmills. Thus, developing improved birch genotypes for not just higher production but also for improved wood quality is necessary to achieve better climate benefits”, says Aureo Aparecido Abreu Junior.

Increased costs for improved seedlings and protection against browsing damage, as well as adaptation of technology and the need for continuous supply of raw material in the industry are some of the challenges ahead for the forest sector.

“Despite the challenges, our work suggests that it is possible to combine both production and climate targets”, Aureo Aparecido Abreu Junior concludes.

He and his colleagues will now continue the work on assessing the climate impacts of e.g. the replacement of traditional spruce plantations with birch genotypes and how climate is affected by changing the product portfolio of birch. They will also investigate how the comparison with birch is affected by different management strategies for spruce, e.g. applying shorter rotation periods to decrease risks with a changing climate in Southern Sweden, such as wind damage and bark beetle outbreaks. The plan is also to do research on the climate impacts of using birch grown in agricultural fields for biochar and possibly investigate the albedo-related effects (how climate is affected by how much solar radiation the earth’s surface absorbs) of increasing the production of broadleaves in Sweden.

Read full research article

Climate effects of improved growth increments and changing utilization strategies for birch (Betula spp.) in Southern Sweden – impact assessment in a life cycle perspective - Environmental Research Communications