Calculation of forestry’s carbon debt

Forestry’s carbon debt is the difference in carbon storage between the forest’s current carbon stock and the storage potential that exists if one consider that there was more stored carbon in the forest before forestry began logging the forests, and hence reduced the amount of carbon in forests. The storage potential, or carbon debt, is the amount of carbon that could be sequestered in the forest if the forest was allowed to grow and become old and carbon-rich. The change that has taken place since the introduction of forestry has generally made the forests younger and less carbon-rich. One may say that the carbon storage has decreased as an indirect cause of forestry. On the website, the carbon debt is calculated for three different fractions of carbon storage in the Swedish forest:

  1. Carbon stored in living trees
  2. Carbon stored in the dead wood
  3. Carbon stored in the soil

Calculation of the carbon debt in living trees

The calculations were made by comparing the amount of biomass within older, protected forest stands with the biomass found outside these old forests, in the forest landscape that is managed by forestry with clearcutting, planting and thinning, etc. The question is how much carbon could be stored in that part of the forest landscape that is currently at forestry’s disposal, forests which are therefore young and carbon-poor, if they were allowed to grow and become old? This is the carbon debt.

The carbon debt in living trees was calculated by using data on the amount of biomass in the Swedish forest landscape. First the amount of carbon stored on average in older and often protected forests was extracted from the data. Then these figures were extrapolated (guessing measured values in an area where data is missing) over the part of the forest land that is currently used by forestry.

However, it has been shown that soils on which the remaining old forest grow, are less productive than the part of the forest landscape that is used by forestry. To put it simply, forestry has taken the best an most productive parts of the forest landscape and left the poorer remains to nature conservation and outdoor recreation etc. Therefore, by simply applying the amount of biomass that exists per unit area in the older forests, over the part of the forest landscape that forestry uses, an error will occur. After all, the forest could grow even “bigger” on forestry’s more productive soils than in the protected forest areas, as such forests grows better. Thus, figures from the National Forest Inventory, describing the relationship between protected forest, forestry’s forests, and productivity, were used to compensate for the difference.

Calculation of the carbon debt in the stored carbon of the dead wood

In the Swedish forests, there are also large amounts of carbon tied up in dead trees which has fallen to the ground. The dead wood is very important for biodiversity and it is also stores a lot of carbon. Therefore, a corresponding calculation was made for dead trees as the one made for living trees.

Regarding dead wood, there are unfortunately no nationwide data like those available for living trees. Hence, summarized data from the National Forest Inventory’s measurements of dead wood  were used. This data is divided into rough decay stages of dead trees, where in Sweden the measurement was made, and if the dead tree was measured within or outside formally protected areas. By using this information and at the same time considering how much forest land is inside and outside the protected forest in different parts Sweden, a corresponding extrapolation, like the one made for the living trees could also be conducted for the carbon stored in dead wood.

Like for living trees, the fact that soils in forest inside the protected, old forest areas is less productive than the soils in forest outside these areas, and more dead wood will hence be created in more productive forests than in low productive, the difference was compensated for.

Calculation of the carbon debt in forest soils

There is also carbon stored in the soil, and logging has a negative effect on soil-bound carbon, because clearcuts are leaking carbon for a period after final harvesting. The data for this calculation was given by the National Forestry Inventory’s ground inventory (Riksskogtaxeringen 2021). The data provides information on, among many other things, tree species and the age of the forest, and the location where the measurement was made in the ground. By adapting the relationship between soil carbon and forest age to a country-wide data on forest age, a country-covering data layer was created that shows the stored carbon of the uppermost soil layer. This is, nevertheless, a very rough calculation with the assumption that forest age is decisive for soil carbon storage.

Although there is a clear connection between the amount of soil carbon and the age of forests, there may be other factors that are important and controls the variation in the soil carbon stock in the forest landscape. There are also shortcomings in the data layer that describes forest age.

Just as with the other two fractions of the carbon debt, a compensation was made for the difference in productivity between protected forests and production forests.

According to the calculations described above, the total carbon debt corresponds to about 3,341 Mton of carbon dioxide, divided between carbon that would have been accumulated in the biomass of standing trees (61%), soil carbon (31%) and dead wood (8%). Today, most of this carbon dioxide is floating around in our atmosphere instead of being embedded in the tree biomass.

It is important to remember that the estimates given in the illustrations on this web page are based on rough estimates and that the reality may look different. Having this said, it is today well known that Swedish forests store less carbon than they would if the forests were older, like forests inside protected areas and in other old-growth forests. It is also known that the reason for this is Swedish forestry, which constantly keeps the forest young and creates new clear-cuts, where most of the carbon stock is removed.

Even if the forestry representatives claim that the biomass taken from forests is used to create climate-smart products, the vast majority of what is harvested becomes paper and other short-lived products that are soon converted into harmful carbon dioxide in our atmosphere.

All calculations will be updated if new data appears, or if better calculations can be made. This may affect the figures given in the illustrations on this web page.

The conversion from carbon dioxide to e.g. number of cars driven in one year was made on open carbon dioxide calculators available online. For the conversion of the amount of carbon dioxide to cars driven per year and number of coal-fired power plants per year, a calculator from the US equivalent of the EPA was used. For calculations of the number of flights to Thailand, a calculator published on the United Aviation website was used. Detailed descriptions of how they estimated the amount of carbon dioxide emitted in these three categories can be found on the respective websites.

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