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Climate benefit greater in managed boreal forest landscapes

The carbon stock in the managed boreal forest landscapes is increasing, while it is relatively unchanged in less intensively utilized boreal forests, where the carbon losses due to forest fires have been significant. This conclusion was drawn in an international research report that analyzes data reported to the UNFCCC by the countries in the “northern coniferous forest belt” during the years 1990–2017.

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The carbon stock in the managed boreal forest landscapes is increasing, while it is relatively unchanged in less intensively utilized boreal forests, where the carbon losses due to forest fires have been significant. This conclusion was drawn in an international research report that analyzes data reported to the UNFCCC by the countries in the “northern coniferous forest belt” during the years 1990–2017 (photo courtesy SLU).

The boreal forests make up as much as 30 percent of the world’s forests and cover about 10 percent of the global land area. Large-scale studies of how the atmospheric content of carbon dioxide (CO2) varies in time and space indicate that the northern forests are carbon sinks. In other words, they absorb more CO2 than they emit into the atmosphere.

First-of-its-kind comparison

For the first time ever, a comparison is now reported of the development of the forest’s carbon stock over time in different parts of the boreal forest belt, which extends through Canada, Alaska (US), Russia, Sweden, Finland, and Norway.

The study “Sustainable boreal forest management – challenges and opportunities for climate change mitigation” is published in a report written by 25 researchers from the six countries, as well as from the International Institute for Applied Systems Analysis (IIASA) in Vienna, Austria.

It is the result of an assignment given at a ministerial meeting in Haparanda, Sweden in 2018, which included the six countries. The assignment was given to the International Boreal Forest Research Institute (IBFRA), an organization that unites forest research institutions in the boreal zone and in which the Swedish University of Agricultural Sciences (SLU) participates.

The work was led by Professor Peter Högberg, Department of Forest Ecology and Management, SLU.

The analysis is based on the data that the countries involved have reported to the United Nations (UN) climate convention, UNFCCC, and provides information on the carbon balance in boreal forests under different management regimes.

The study compared countries with relatively intensive forestry (Norway, Sweden, and Finland) with countries where forests are used less intensively (Canada and Russia) or not at all (boreal Alaska).

The measure used for the intensity of forestry was how many percent of the forests’ total carbon stock is harvested each year.

The study covers the period 1990 to 2017. Further back, comparable data from some of the six countries are missing. A challenge for the researchers has been to compare data that have been collected in different ways and are of different quality.

Carbon stocks increase in managed boreal forests

In Sweden and Finland, this is 1.5 percent, compared with 0.9 percent in Norway, 0.3 percent in Canada’s managed forests, and 0.1 percent in Russia’s forests. In countries with forestry, rotation forestry with clear-felling is commonly applied.

The study shows that the forests’ carbon stocks increased in the countries with intensive forestry. During the period of 1990–2017, the carbon stock in the trees increased by 35 percent, seen as an average over the entire forest landscape in the Nordic countries.

In the countries with less intensive forestry, the changes were significantly smaller (a few percent plus or minus).

The report does not support claims that unused forests contribute the greatest climate benefit, said Peter Högberg, who is a professor of forestry at SLU and has led the work on the report.

The countries’ reports to the UNFCCC also include estimates of changes in the carbon stock in the soil. The study shows that the carbon stock on mineral soils in the intensively managed Nordic forests increases twice as fast in comparison with the countries with less intensive forestry.

On the other hand, significant carbon losses and nitrous oxide (N2O) emissions occur from drained peatlands.

Despite this, the Swedish forest soils are on average a carbon sink. In Finland, where the proportion of peatlands is higher and where over 50 percent of the peatlands are drained, the emissions from peatland soils are of the same magnitude as the carbon sink of upland forest soils.

Age class distribution and forest fire

Differences in the forest carbon sinks between Nordic managed forests and unused vast forest areas in Russia, Canada, and the US state of Alaska are discussed in the report.

One of the driving factors is age class distribution; Nordic managed forests are on average younger. Another reason is the large losses of carbon in the forest fires that occur much more often in the less intensively managed and unused forests.

In Alaska, Canada, and Russia, an average of 0.5–0.6 percent of forest area burns each year, compared with 0.01 percent in Sweden and even less in Norway and Finland. The area burned is thus at least 50 times higher in the less intensively managed forests.

Today’s low fire frequency in the Nordic countries is due to effective fire fighting, motivated by the economic value of the trees. During the period 1500–1850, when timber was not valued in the same way, roughly 1 percent of the area burned each year. Among other things, fires were started to improve the grazing of cows, sheep, goats, and reindeer in the forests said Peter Högberg.

The report affirms that the carbon stock of the boreal forests is large, that unused forests suffer to a very large extent from carbon losses in fires, while the managed forests show a rapid build-up of the carbon stock at the same time as they supply raw materials to the bioeconomy.

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