Dr Antti Kilpeläinen and Professor Heli Peltola explain how boreal forests and forestry play a crucial role in climate change mitigation.
Boreal forests and forestry play a crucial role in the global carbon cycle and climate change mitigation. The use of boreal forests and forest-based biomass (timber and energy biomass) responds to the increasing demand for renewable energy and wood-based materials. Using wood-based materials and energy biomass from sustainably managed forests has great potential for the long-term reduction of carbon emissions.
Sustainable climate change mitigation requires increases in carbon sequestration and carbon stocks in forest ecosystems (soil and tree biomass) and related technosystems (i.e. outside forests). A consideration of existing forest sinks is also included in the land use, land-use change and forestry (LULUCF) sector proposal of the European Commission under the EU´s Climate and Energy Framework, aimed at a total emissions reduction of 40% by 2030 for all sectors, as part of the Paris Climate Agreement. In the LULUCF proposal, the forest sink is allowed to compensate for the emissions of a member country only above a forest (management) reference level.
Sustainable forest-based bioeconomy
A solid base for the development of a sustainable forest-based bioeconomy requires an understanding of the impacts of forest management and harvesting intensity, and climate change, on forest resources and their development in the future. This is because modifications in forest management may be needed in order to increase biomass production and carbon stocks in forests per unit land area, and forest biomass use to substitute for fossil based materials and fuels, respectively.
In addition, the adaptive management of forests should consider increasing abiotic and biotic risk to forests, which affects the resilience of forests to changing climate. Proper adaptive forest management sets a sustainable basis for the mitigation of climate change based on forests and their utilisation in a bioeconomy.
The role of forest management in climate change mitigation
Generally, forest management that enhances forest carbon sequestration in boreal conditions increases the climate change mitigation potential of forest biomass production and utilisation. For example, the use of better growing tree species and genotypes, maintenance of higher stocking in thinning than currently recommended, and fertilisation will enhance the climate impacts of forests by increasing carbon sequestration and carbon stocks in trees and soil in boreal environments.
At the same time, the quantity and quality of produced timber and energy biomass may also be increased. Timber yield, share of pulpwood and saw logs, and timing of harvesting also affect the substitution impacts of wood-based materials as well as the economic profitability of forest production.
The use of forest-based biomass in climate change mitigation
The temporal deviation that exists between carbon sequestration and the harvesting of forest biomass affects the predicted mitigation benefits of forest-based biomass production and utilisation. The increased harvesting intensity of managed forests decreases ecosystem carbon sequestration and stocks and temporarily increases the amount of carbon in the atmosphere. This is opposite to use of lower harvesting intensity. On the other hand, the climate impacts of forest-based biomass also depend on the fossil-based materials and fossil fuels that they substitute.
The resource-efficient use of wood-based materials and energy biomass generates climate benefits when they replace fossil-based materials (e.g. concrete, plastic, and steel) and energy (e.g. coal and oil). The use of wood-based materials with long lifespans prolongs the residency of carbon in the technosystem (outside forests) and increases climate benefits, compared to products with a short life span.
Climate benefits can be also account for the cascading use of wood-based materials. This could prolong the residency of carbon in the technosystem and generate climate benefits through the substitution of fossil-based materials. Wood-based materials can also be used as energy at their end-of-life stage, in opposite to many fossil-based products.
The assessments of impacts for existing forest carbon stocks, forest management practices, and the harvest intensity of forests are complex. Therefore, the climate impacts of forests should be studied jointly so as to consider the efficiency of alternative management measures in both sequestering carbon in forests and producing timber and energy biomass for substitution.
It is important to identify possible trade-offs and win-win situations in a sustainable forest-based bioeconomy. This is needed to support decisions involving forest management and land use that can provide sustainable forest resource use and climate-positive impacts. The adaptive management must also consider uncertainties in impacts of climate change on forests for different time spans and regions.
Life-cycle assessment (LCA) of forest production
The entire life-cycles of forest biomass and wood-based materials should be considered in assessing the total climate impacts of forest biomass production and biomass utilization. This is possible by integrating forest ecosystem modelling and the life-cycle assessment (LCA). By using ecosystem modelling, the dynamics of changes in the above- and belowground carbon stocks of forests and timber yield may be evaluated under different management scenarios. Consequently, carbon emissions from, for example, management operations, such as the thinning and transportation of timber, and the conversion of timber into wood-based materials, can be tracked according to timber yield.
Substitution impacts occur in the technosystem when the wood-based material is converted into a wood product, and the impacts crucially depend on the fossil carbon being substituted. When the carbon stock of wood products increases in the technosystem, wood-based materials also get climate benefits, but degradation of the stock produces carbon emissions. Very often, wood-based material is used only partially in a final product, which makes accurate assessment of the climate impacts challenging.
As a result of the comparison of forest- and fossil-based production systems in an LCA, displacement factors can be calculated to estimate the substitution impact of the wood products. These factors indicate the amount of carbon emissions that are avoided when wood-based material are used to replace alternative, but functionally equivalent, non-wood materials (tonnes of carbon emissions reduction per tonne of carbon used in wood material). The displacement factors are product-specific, and ideally consider the impacts of reduced carbon stocks in forests due to biomass harvesting, and the impacts of changed carbon stocks of wood-based products in the technosystem.
Calculations of the total climate impacts of wood-based materials vary, depending on emissions from the substituted fossil-based material and energy, and the functional unit used in the calculation. The displacement factors of the wood materials are also dependent on how forest-based biomass is produced. The total climate impacts will vary substantially over time, also depending on the prevailing forest structure and the initial conditions set for the study, but the LCA approaches to forest biomass production and utilisation will assist in defining effective options for mitigating climate change in forests and forestry.
The FORBIO project will provide different stakeholders with the required know-how on the possibilities offered by sustainable management and utilisation of boreal forests for climate change mitigation.
Dr Antti Kilpeläinen
Professor Heli Peltola
FORBIO project co-ordinator
School of Forest Sciences
University of Eastern Finland
+358 50 383 3263 (Kilpeläinen)
+358 40 588 0005 (Peltola)