Lowering forest harvests in Finland would be beneficial for climate
The study of the climate impacts of forest harvest level highlights trade-offs and uncertainties. The recently published study by Kalliokoski et al. (2020) is the first one combining a divers set of climate effects from CO2 sequestration and harvest to surface albedo and aerosols. The study shows that when accounting simultaneously all the effects, lowering harvests down to 50% of current annual increment, would be beneficial for climate within 50 years timeframe.

In our study (Kalliokoski et al. 2020, https://www.frontiersin.org/articles/10.3389/ffgc.2020.562044/full) we analyzed the climate impact of forest harvest level in Finland. This is the first time, when one study includes such a comprehensive set of different climate effects; CO2 in trees, soil and harvested wood products (HWP), avoided fossil emissions aka substitution due to increased wood use, and biophysical factors in terms of surface albedo and forest-related aerosols.

The main finding of the study was that when accounting simultaneously all above-mentioned effects lowering harvests from the current level, down to 50% of current annual increment, would be beneficial for climate within analysed 50 years timeframe. The combined impact of all effects in terms of radiative forcing (RF) was the most cooling in that scenario.

Also interesting result was that both on stand level and country-wise, radiative forcing change due to surface albedo and secondary organic aerosols (SOAs) more or less counterbalanced each other. This result highlights that conclusions of boreal forest studies including only CO2 and surface albedo effects and asserting that expanding forest area in high latitudes could increase global warming may not hold. However, the results concerning the aerosol effect should be regarded as the first attempt to compare them with other effects having very high uncertainty especially in cloud dynamics.

Analysis also showed that displacement factor (DF) should be at least 1.7 tnCO2/tnCO2 for harvest scenarios higher than baseline (65 mill.m3/year) to reach climate neutrality within next 50 yrs. Seppälä et al. (2019) stated that current average DF of HWPs is ca. 1.1 in Finland. Current average DF is much lower than that when calculated for wood harvested from forest (not for HWPs) as we did in our study (see e.g. Soimakallio et al. 2016). Further, "substitution" is a property of the technosphere, which can change without any changes in forests or the forest sector. Without including this effect, i.e. accounting for the changes in the biosphere, differences between scenarios were clear, 50% scenario having the most negative RF.

These results should act as a caution mark for policy makers who are emphasizing the increased utilization of forest biomass for short-living products and bioenergy as an efficient measure to mitigate climate change.

References

Kalliokoski, T., Bäck, J., Boy, M., Kulmala, M., Kuusinen, N., Mäkelä, A., Minkkinen, K., Minunno, F., Paasonen, P., Peltoniemi, M., Taipale, D., Valsta, L, Vanhatalo, A., Zhou, L., Zhou, P. and Berninger, F. 2020. Mitigation Impact of Different Harvest Scenarios of Finnish Forests That Account for Albedo, Aerosols, and Trade-Offs of Carbon Sequestration and Avoided Emissions. Frontiers in Forest and Global Change 3:562044. doi: 10.3389/ffgc.2020.562044.

Seppälä J, Heinonen T, Pukkala T, Kilpeläinen A, Mattila T, Myllyviita T, Asikainen A, Peltola H, Effect of increased wood harvesting and utilization on required greenhouse gas displacement factors of wood-based products and fuels, Journal of Environmental Management 247: 580–587, 2019

Soimakallio S, Saikku L, Valsta L, Pingoud K, Climate Change Mitigation Challenge for Wood Utilization – The Case of Finland, Environmental Science & Technology, Environ.  Sci.  Technol. 50: 5127−5134, 2016