Sink or Source - Northern forests at a cross-roads

Tropical forests get most of the attention, but northern forests are under growing threat too. A new report by AirClim explores the risks—and what can be done to protect them.

In the report published in March 2025, northern forests are defined as the boreal and temperate forests of industrialised countries in the northern hemisphere. They comprise about 40% of the global forest area, and about the same share of the global forest carbon stock.

All northern forest countries are in Annex 1 of the UN Climate Change Convention (UNFCCC).  As non-annex 1 countries can receive financial support for halting deforest-ation and protecting their forests (under the UN REDD+ programme), they can also be held accountable for progress. The same provisions do not apply to Annex 1 countries. In general it is assumed that forests in Annex 1 countries are not under threat, or at least less threatened than tropical forests.

A key message of this report is that this is a misconception. 

Northern forests are experiencing massive losses of ecosystem integrity, biodiversity and carbon storage capacity, and have done so for decades. The main drivers behind this development are climate-induced increases in natural disturbances and unsustainable forest management, including exploitation of the last remaining tracts of old-growth forests, possibly in combination with decreased positive growth effects of warmer climate and CO2 fertilisation.

Increasing demand - a main driver

An underlying, ultimate driver is the ever-increasing demand for forest products. The consumption of industrial roundwood (for paper and wood products) almost doubled between 1960 and 2010, and is projected to increase by another 75% by 2050. About 75% of the global sawn wood and pulpwood supply comes from northern forests. 

Disturbances, such as wildfires and pest outbreaks, are an integral part of northern forest ecosystem dynamics, but have become more frequent and intense in recent decades due to global warming. The frequency and extent of fires are currently higher than at any time over the last 10,000 years. Heat and water stress, which weakens tree resistance, has also caused a dramatic increase in insect outbreaks across the northern forest region. In British Columbia, an unprecedented outbreak of the mountain pine beetle in 2008 affected 37 million hectares of boreal forest. In 2000 and 2001 the Siberian silk moth damaged more than 10 million hectares of larch forest in latitudes where this insect had rarely been observed before. The trends for drought and wind disturbances are similar, and examples of unprecedented disturbance events are manifold. Further increases are projected. At 3oC of mean global warming – which is where we are heading with current climate pledges from the world’s governments – the average annual area burned in the Mediterranean region and interior Alaska, for example, is expected to increase by 50% over the next 50 years.

Clear-cut forestry degrades ecosystems

About 75% of the northern forest area is managed for timber production. The prevailing management model, rotation forestry with clear-cut harvesting, is causing ecosystem degradation, threatening biodiversity and is unfit as a management model for climate mitigation. Additional areas are continuously being exploited and degraded.

Less than 10% of the northern forest area is under some level of protection, which is a lower level than in tropical forests (17–26%). About one-third of boreal forests is still largely intact primary or old-growth, but due to a lack of sufficient protection this area is diminishing at an alarming rate. In the temperate region, only about 1% of broad-leaved forests is substantially unaltered and considered old-growth. These forests are strongholds for the natural biodiversity of northern forests and generally store large amounts of carbon, sequestered over centuries or even millennia. The remaining northern old-growth forests are estimated to provide at least 10% of the global ecosystem carbon sink. 

The combined effects of increasing natural disturbances, forestry and insufficient pro-tection for remaining old-growth forests are severe and include loss of forest ecosystem integrity and resilience, a growing biodiversity crisis and depletion of the northern forest carbon sink.

1,400 red-listed species in Sweden´s forests

In Sweden and Finland, industrial rotation forestry and large-scale clear-cutting have a longer history than in other parts of the northern hemisphere and have transformed 90% of the forest area over the last 70 years. As a result, 1,400 red-listed species in Sweden are considered very negatively affected by forestry. In Finland, 32% of red-listed species (2,113 species) are forest-dwelling. It is reasonable to assume that the effects on forest biodiversity seen in these countries reflect  what can also be expected in other parts of boreal forests, unless management practices and intensity changes.

While the net global forest carbon sink increased between 1990 and 2020, the northern forest sink decreased by 23%, and the rate of decline accelerated over the period. Unless this trend is reversed, northern forests may shift from an overall net carbon sink to a carbon source as early as 2060. Passing this critical tipping point would start a process during which part of the huge carbon stock in biomass and soils is released into the atmosphere, causing further warming and further carbon losses in a self-reinforcing loop that results in runaway warming.

Historically, large areas of northern forests (primarily in the temperate zone) have been lost. However, recent human impact on northern forests does not include deforestation to any notable extent. Over the last three decades the extent of deforestation and reforestation has been just 0.3% and 2.3% of the total forest area, respectively, and the overall northern forest area has increased by 2%. Nevertheless, governments of northern forest countries are relying heavily on reforestation measures in their national commitments (NDCs) under the Paris Agreement, while very little – if any – attention is paid to the potential for increasing the carbon sink of existing forests. In total, northern forest countries have committed to 160 million hectares of reforestation and afforestation by mid-century – equal to the entire land area used for agricultural production within the European Union. It is unlikely that this can be realised without severe land-use conflicts and complex trade-offs for food security, biodiversity and human livelihood.

A simple explanation for the over-reliance on reforestation and afforestation is that it offers an appealing form of carbon removal for governments and industry. Unlike forest protection and changes to forest management, it does not imply harvest reductions that would affect the supply of raw materials to the industry and energy sectors, and until land is actually allocated for new forests, the land-use conflict may conveniently be overlooked.

Intensified forestry is not an option

Intensifying rotation forestry and increasing harvests is frequently advocated as a strategy to increase the climate mitigation effect of forests. The rationale for this is that harvested wood is supposed to replace fossil fuels and materials – such as steel and cement – that are produced using fossil fuels. In addition, it is assumed that part of the harvested wood will end up as persistent carbon pools in long-lived products (such as wooden buildings). If one tonne of carbon removed from the forest substitutes more than one tonne of carbon emissions from fossil fuels (i.e. a substitution factor of 1.0 or higher), this strategy would be viable. However, recent studies on the substitution effect indicate  that the substitution factor is between 0.4 and 0.8, i.e. the climate effect is negative. One reason for this is that only 40% of the roundwood harvested globally is used in long-lived products, and only 44% of carbon in such products remains stored for longer periods than 25 years. This means that from a tonne of carbon removed from the forest today, 830 kg will return to the atmosphere before 2050, and most of it even before 2030. It has actually been shown that a tree left to die and decompose in the forest is a more durable carbon pool than if the same tree is logged, processed and used, given the present product mix.

The carbon cost of timber harvest: 0.8 Gt per year

Wood harvesting and use are not, as often claimed, “carbon neutral”. Such claims assume that carbon losses from new harvests are offset by sequestration from the growth of broad forest areas. This is misleading, since the climate consequence of new harvests cannot logically be altered by forest growth that would have occurred anyway. The true carbon cost of present global timber harvesting is 0.7–0.8 Gt per year, and the projected increase in demand would increase this cost by around 0.2 Gt by 2050. Thus, increasing rotation forest management is not a viable climate mitigation strategy.

Bringing greenhouse gas emissions as close to zero as possible is imperative in order to limit global warming to 1.5oC. In addition, negative emissions, i.e. active removals of carbon from the atmosphere, in the range of  2 to 6 Gt per year will be needed. Land ecosystems, especially forests, have the potential to deliver this crucial ecosystem service. It has been estimated that existing forests can store an additional 139 Gt of carbon under appropriate management. Almost half of this potential is in the northern forests. In addition, reforestation measures have the potential to store 87 Gt. For comparison, annual global carbon emissions are around 11 Gt.

In order to protect and restore the carbon sink of northern forests, as well as their biodiversity and ability to adapt to shifting environmental conditions, including further warming, the following strategies are essential:

Reduce greenhouse gas emissions rapidly in line with the long-term target of the Paris Agreement. 

Any further increment of warming will increase the extent and intensity of disturbances in northern forests, causing further carbon losses and damage to the resilience of forest ecosystems.

Ensure efficient protection of at least 30% of all northern forest ecosystems, including all remaining primary and old-growth forests.

Safeguarding ecosystems and their roles in adaption and mitigation is fundamental to climate resilient development.

In reaching the 30% target, protection of remaining primary and old-growth forests should be a first priority. In addition to the direct negative climate effects of timber extraction, exploitation of these forests will inevitably cause loss of resilience, making them more vulnerable to fire, pests and other disturbances, increasing the risks of further carbon losses. It will also increase the need for future restoration measures.

To be effective, however, the 30% tar-get must be met on a regional scale. A repre-sentative, interconnected network of protected, near-natural ecosystms – a green infrastructure – must be planned and implemented all over the northern forest region.

Halt ecosystem degradation of managed forests and restore their resilience and ability to store carbon. 

Extending the stand volume of existing forests has greater positive short-term effects on the carbon balance than any other possible change in forest management. This can be done by extending the rotation periods, which might be feasible within the framework of rotation forestry and its focus on timber production. It will not, however, improve ecosystem resilience or release the pressure on forest biodiversity more than marginally. Abandoning rotation forestry and clear-cutting and shifting to forest ecosystem management, on the other hand, offers a viable pathway not only to increase the northern forest carbon sink, but also to simultaneously address the biodiversity crisis and strengthen ecosystem resilience. 

An overarching principle of ecosystem management is that forestry should minimise its impact on ecosystems. Harvesting is carried out selectively or in very small gaps. Tree species diversity, age distribution and structural diversity should, as far as possible, emulate natural conditions at every specific site. Forests are regenerated naturally. Since forest ecosystem management operates with considerably larger stand volumes than rotation forestry, the carbon stock per area unit is bigger, and a transition to ecosystem management thus utilises a bigger share of the natural carbon storage potential than does rotation forestry.

Shifting from rotation forest management to ecosystem management is in fact a form of ecosystem restoration, conducted within the framework of timber-producing forestry. A rough estimate of the climate mitigation effect of such a transition over the entire managed northern forest area shows the potential to increase the annual carbon sink by about 0.8 Gt, which corresponds to 20% of the present global forest sink.

Ecosystem forest management is probably the most promising solution for achieving sustainable forest management within a context of climate change.

Roger Olsson

Wendel Trio

Link to the report:

https://www.airclim.org/publications/sink-or-source-northern-forests-crossroads