Impact of longer rotation regime to overall carbon sequestration
Limiting global temperature rise by retaining atmospheric carbon dioxide concentration according to the Paris Agreement has highlighted the meaning of forest carbon sequestration. At the same time the increasing global demand for material usage calls for renewable low-carbon raw material substitutes. In public discussion forest management objectives are occasionally seen overlapping even though timber management planning could be combined with carbon sequestration objectives.
One way of enhancing carbon sinks along with biomass production is by applying longer rotation length forestry. Lengthening rotation by postponing final harvesting increases carbon stock in the biomass through sturdiness of trees, hence increasing the long-term average standing stock volume and thus increasing the long-term carbon removals to the biomass from the atmosphere. However, approximately up to two thirds of the forest carbon stock is in the soil. Impacts of the longer rotation to the forest soil carbon stock varies and depends on selected species, their stand dynamics, and the applied forestry context.
Photo by Julian Hochgesang / Unsplash.
Due to decreased frequency of the carbon feed from harvest residues into the soil combined with decreased litter production, longer rotation might even decrease the soil carbon storage in the long run. In addition to the biomass and soil, the rotation length also affects the carbon stock in wood products. In the extended forestry system, the positive climate impact of the increased carbon sequestration into the biomass will transfer, to some extent, also into increased carbon storage in long lasting wood products. All of these components; biomass, soil, and wood products, need to be included for understanding the overall climate impacts of our forest management planning decisions.
Due to decreased frequency of the carbon feed from harvest residues into the soil combined with decreased litter production, longer rotation might even decrease the soil carbon storage in the long run.
Importantly, even though postponing harvesting might decrease timber income, forest revenues and value can increasingly be improved by realizing the carbon sequestration potential. In terms of revenue, tradeable forest carbon units can provide an additional means for income generation for the forest owner while supporting increase of forest carbon sinks. The key is to find the right balance and comfort zone between harvest incomes and carbon units; a scenario that fits the specific context, time span, and the interests of the forest owner. Likewise, we are seeing signals of forest becoming an increasingly lucrative asset class due to its significant and very cost-efficient climate benefits. This will likely be reflected also in an upward trend of the forest land market value.
At least on a theoretical level, jumping from calculation of the net present value into calculation of net present carbon sink is not that big of a leap, and would allow adjustable weight for temporal importance of the carbon sinks. Who knows, maybe in the near future we’ll be doing valuations for protected forest areas, for example, based on their net present carbon sequestration potential and carbon storages.
Victoria Poljatschenko, Consultant Juho Penttilä, Head of Carbon Services
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