The brochure The climate benefits of the Nordic forests was produced and presented by Nordic Forest Research (SNS) and the Nordic Council of Ministers in 2017. Here, we add more explanations about the assumptions and measurements presented in the brochure.
Text and facts: Tomas Lundmark (firstname.lastname@example.org) och Mats Hannerz (email@example.com)
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The forest contributes to climate benefits in two ways
1: Carbon stored in the forest
A forest absorbs carbon dioxide from the atmosphere through photosynthesis and releases some of it through respiration. The surplus is converted to carbohydrate and used for tree growth. When net growth products are retained in the forest, there is long-term carbon storage. The forest acts as a carbon sink.
This annual climate benefit remains as long as the biomass stock increases, but there is an upper limit to how dense a forest can be. When the trees age, their net growth decreases. Trees die, the wood degrades, and carbon dioxide is released back into the atmosphere. Old forests capture as much carbon as they emit. A forest without net growth does not add any further climate benefits.
750 kg carbon dioxide
One cubic metre of stem wood contains carbon equivalent to approximately 750 kg CO2. One average forest hectare in the Nordic region, growing at a rate of 5 cubic metres per year, therefore annually stores the equivalent of about 4 tonnes of carbon dioxide in its stems. This corresponds to the emissions from a diesel car that has travelled about 20,000 kilometres.
The order of magnitude of the annual storage benefit at a stand level is simply the net growth minus mortality, i.e. the increase in biomass. At a forest landscape level, the storage benefit is the average increase in biomass, when growth, mortality and harvests are accounted.
One fresh cubic metre stem wood contains about 400–450 kg dry matter (varies depending on tree species, silviculture etc.). Carbon accounts for 50% of the dry matter (+/- a few percent) – > 200–225 kg carbon. One kg carbon corresponds to about 3,7 kg carbon dioxide (atomic weight of carbon is 12, oxygen 16). This gives the approximate figure of 750 kg CO2 per cubic meter.
2: Substitution – displacement of fossil carbon dioxide
A second way of contributing to climate benefits from the forests is through substitution of fossil raw materials. When wooden products are replacing fossil products, no “non-renewable” carbon is added to the atmosphere. This substitution can relate to district heating with wood instead of coal, natural gas or oil or the use of wood fibres instead of plastics. Building materials from wood also lead to substitution, since it replaces more climate-impacting materials such as cement and steel. Cement emits large quantities of carbon dioxide in the production process.
By burning wood for making energy, carbon dioxide is of course also released to the atmosphere. However, this carbon is part of a natural cycle where it is taken up by new trees. The use of growing biomass for energy production is therefore considered carbon neutral.
Substitution is a measure of how much fossil greenhouse gases that are displaced by the wood-based products. The magnitude of the substitution depends on the products and processes where the wooden material is used. The least efficient use would probably be to burn the wood on an open fire to produce heat – unfortunately a common use in many parts of the world. More energy-efficient processes and more long-lived products result in higher substitution effects.
To strive for high substitution rates, solid wood products (sawn wood, wood-based panels etc.) or efficient energy generation should be prioritized. Pulp and paper has far lower substitution effects. The substitution factor can be expressed as units of fossil C emissions being avoided per unit of C in a wood product. Here, Sathre and O’Connor (2010) performed a meta-analysis of greenhouse gas displacement factors, and found that most of them were in the range of 1-3 units of fossil C per unit of C in wood. A case study of the Swedish forest industry came to the conclusion that the substitution was in the range of 500-1400 kg CO2 per cubic meter of harvested biomass (Lundmark et al. 2014). These figures include the actual replacement of fossil products, both in our country and when the wood is exported. The energy needed for harvest and production has also been considered in the figures.
One cubic meter displaces 500–800 kg CO2
The substitution factor for a whole region or country will depend on the mixture of products and uses. In our calculations, we have assumed that the current use of forest products corresponds to a substitution effect of 500 kg CO2 per cubic meter of harvested wood.
In a future scenario, new products such as more long-stored use in house building and more efficient energy generation will raise the substitution factor. We have assumed 800 kg CO2 per cubic meter in our future analyses.
The annual climate benefit of the Nordic forests
The National Forest Inventories provide extensive and detailed information about harvests and growth in the Nordic forests. In our diagrams, we have calculated the annual benefit for the three most forested countries Finland, Sweden and Norway over a 50-year period from 1965. This is made from:
1 – the annual increase in standing volume. The increase is the net result of growth, mortality and harvests. This climate benefit is positive as long as the wood stock increases. We have assumed that each cubic metre of stem wood sequesters 750 kg of carbon dioxide, and stores the same amount if the trees are left in the forest.
2 – substitution effect of harvested wood. When trees are harvested and used, they replace other non-renewable raw materials. The substitution factor depends on the products and processes where the wood is used. In the diagrams, we have assumed a mixture of products corresponding to the current use of wood. This corresponds to a substitution effect of 500 kg carbon dioxide per cubic meter wood.
3 – the sum of increased wood stock and substitution. This calculation shall not be misinterpreted as double counting. In a forest landscape, there will be a mixture of harvested stands and stands still growing. As long as the harvest does not exceed the net growth at a regional level, substitution and storage benefits will both arise.
The calculations show that the annual climate benefit increases over time. Over all three countries, it is almost twice as high today as it was fifty years ago, about 150 million tonnes compared with 83 million tonnes in 1965.
In Sweden and Finland, substitution accounts for the bulk of the climate benefit. Norway’s climate advantage mainly consists of an increase in living wood stock.
Manage or preserve the forest – what are the pros and cons?
Nearly all forests in the Nordic countries have been managed for a long time. A topical question is about the impact of management on climate – is it better to manage the forest or to use it as a carbon store? In the short term, it is better for the climate to leave the forest as it is and allow the carbon stock to increase. However, this is only possible up to a certain limit. Trees can continue to grow for a long time, that is true. However, at a stand level, the declining growth of senescent trees will be accompanied by dying trees and degrading wood. When the trees die, carbon will eventually be released back to the atmosphere. In an old forest, as much carbon will be captured as will be emitted. A forest without net growth will thus not add any further climate benefit.
In the longer run, it is therefore better for the climate if the forest is used and managed. The more the forest grows, the more carbon is captured, and the more wood can be used for substitution. A managed forest landscape has a mosaic of stands with clear cuts releasing carbon, and growing stands capturing carbon. As long as the net growth exceeds the harvest, the carbon stock increases and this occurs on top of the substitution effect. When old trees with reduced growth are replaced with young trees, net growth increases. Harvesting trees is therefore the most important tool to maintain high growth.
The managed forest is the winner in the long run
The figure below shows the cumulated climate benefit of two options for using a forest landscape in southern Sweden, corresponding to the county Småland. In the blue option, harvest is halted and all forest is preserved allowing it to develop freely. In the green option, we continue to manage the forest as we do today by harvesting the net growth.
In the preserved forest, we see an initial increase in stored carbon. We have a climate benefit as long as the wood stock continues to increase. When the forest ages, growth will decrease, and trees die due to storms, root rot and insets. The climate benefit decreases.
The managed forest delivers climate benefits by replacing climate-negative products (substitution) with forest products. In addition, it continues to growth because mature stands are harvested and replaced by new, growing forests. In the longer term, the cumulated climate benefit will be much higher in the managed forest.
Since climate benefit is determined by growth, the benefit will increase if we are more active in our forest management. Nordic estimates show that growth in individual stands can increase by 30–100% as a result of changing tree species, using genetically improved seedlings or fertilizer application. The more the forest grows, the more it contributes to a fossil-free society. Meanwhile, we have the option to preserve forests for biodiversity, social values and other interests.
The figure below shows that the preserved forest has a better climate benefit initially. After a period of 80–100 years, the managed forest scenarios will surpass the preservation scenario. One can thus argue that preservation is best for the urgent climate mitigation needs, in a few decades perspective.
However, one must also consider the current use of paper, wood and biofuel. If this will be replaced by plastic, oil, coal and cement, the climate will be the loser.
Read more about managed and preserved forests:
Lundmark, T., Bergh, J., Hofer, P., Lundström, A., Nordin, A., Poudel, B.C., Sathre, R., Taverna, R., och Werner, F. (2014) Potential roles of Swedish forestry in the context of climate change mitigation, Forests 2014, 5(4), 557-578.
More about the Nordic forests
Sparsely populated but forest-rich countries
Sweden, Norway and Finland are three of the most forest-rich countries in Europe. Of Europe’s 215 million hectares of forest land (the whole of Europe except Russia, data for 2015), there are over 62 million hectares in these three nations. Denmark’s approximately 600 000 hectares and Iceland’s 49 000 hectares of forest land also contribute to the fact that the Nordic region has 19% of Europe’s wood stock.
The Nordic countries may therefore have a special responsibility in using the forest to combat of climate change!
Forest data 2015, State of Europe’s forests (FAO). Land classified as “Forest”. All European countries except Russia.
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