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Climate benefits of the forest – a balancing act in prioritisation

boreal forest with green mosses on the ground. Photo.
The forest has many benefits. What climate benefit you get by leaving the forest for storing carbon, or by extracting biomass that can replace fossil raw materials, largely depends on the time horizon. Photo: kn1/IStockphoto.

The forest is currently at the centre of an intense debate. It concerns, in simplified terms, which climate benefits the forest can provide, either by sequestering carbon in standing forest, or by being used to substitute fossil fuels and fossil-intensive materials.

In a new literature review from the Centre for Environmental and Climate Science (CEC) at Lund University in Sweden, Markku Rummukainen, professor of climatology, has looked at existing knowledge of the forest’s possible climate benefits and put it in context, such as how can we obtain the greatest possible climate benefits from the forest, and what does research say? The answer is – it depends, with especially the temporal perspective being a significant factor.

“The time aspect is key when it comes to whether the forest provides most climate benefit by staying in place and sequestering carbon, or through us extracting biomass to substitute fossil energy and fossil-intensive materials with”, says Markku Rummukainen.

The next few years are important

From a time-perspective of up to several decades, the more forest that is allowed to stay in place, the more climate benefit can be derived from it. This is because a standing forest sequesters a lot of carbon. Felling leads to greenhouse gas emissions and at the same time it takes some time before a newly established forest has taken up as much carbon dioxide than the forest would have done, had it stayed in place. This is significant as it is important, if we are to achieve climate goals, to limit emissions in both the short and long term. To limit global warming to 1.5 degrees requires the world’s emissions to be halved by 2030, and to reduce at around zero by around 2050.

“One argument for letting the forest stay in place, with maximum carbon sequestration as a result, would therefore be to buy time for society’s climate change mitigation over the next few very important years”, says Markku Rummukainen.

The climate benefits of substitution can vary

Weighing against this is the need for phasing out of fossil fuels and other fossil-intensive materials, such as through replacing them with biomass. However, calculating the climate benefit of such substitution is not straightforward, as the benefits vary depending on what is being replaced, the length of the products’ lifecycle, assumptions about consumption patterns, about the forest’s carbon sequestration, and so on. If, for example, biomass is extracted for use as bioenergy, there is an immediate climate impact when the biofuel is combusted. Even so, bioenergy is regarded as climate-neutral in certain contexts, partly based on emissions being “registered” within the framework of land use and land use change, rather than the energy sector, and partly because growth of new biomass will eventually sequester as much carbon as was released during combustion. However, it takes time to replenish the stored carbon. In the case of bioenergy, it can take several decades, especially if the carbon sequestration that would have continued in the forest if it had not been felled is factored in. If, however, the biomass is extracted to create a product with a long lifetime, the product also binds carbon for a long period. And if such a product is recycled instead of being combusted, it may live on for more years before the carbon reaches the atmosphere in any final combustion.

“Bioenergy and bio-based products can contribute to society’s transformation, especially in the long term, but also cause a net emission over the next few decades compared with other options”, states Markku Rummukainen.

Four tall houses close to the water. Photo.
The forest also has an important role in the transition to a fossil-free society. Biomass extracted for long-lived products, such as wooden houses, gives products which also binds carbon for a long time. Photo: Alexanderstock23/Shutterstock

Different results

To further complicate the matter, when calculating various climate benefits from the forest, there are a number of other uncertain, or at least complicated, factors to take into account. For example, there are different results regarding how much carbon the forest sequesters in biomass and in the soil, and how long it takes before newly planted forest takes up so much carbon that it can compensate for a previous felling. Different assumptions used in making calculations also engender uncertainty. This applies, for example, to the question of how the forest itself will be affected by climate change. In addition, carbon dioxide emissions from biomass are registered in different ways, depending on what it has been used for. Emissions relating to bioenergy, for example, are registered in the country the biomass came from, instead of where the bioenergy is used, whereas it is different for harvested wood products.

Overall, Markku Rummukainen, considers that a term such as “climate-neutral” cannot be used in a general sense, as it contains far too many different aspects and variables that must be considered. Again, the time aspect is key, but that bioenergy also involves emissions, even if these are not attributed to the energy sector, also matters.

“It is important that we are clear what we are talking about in this context, what assumptions are built on, what time horizon is being considered, who will deal with the emissions that arise despite everything, how fast sequestered carbon is replenished, and how bioenergy and products are placed in overall societal transformation, now and in the future.”

Other benefits to consider

Markku Rummukainen points out that there are also many other societal benefits besides climate benefits to consider when talking about the forest. There is conservation of biodiversity, timber production and social values such as recreation and outdoor life – everything is relevant to the “prioritisation balancing act” that he talks about. “Conflicting goals may exist and of course need to be resolved – there may be different views about which priorities are to take precedence in which forest”, he says.

Synergies are important in this context. Promoting nature conservation or outdoor life may, for example, in itself provide a type of positive climate effect when the forest stays in place. In the same way, measures with an extended rotation period and forest management for continuous-cover forestry lead to benefits for nature conservation and recreation, while also providing a certain climate benefit.

Man fishing with forest in the background. Photo.
There are also many other societal benefits to consider when discussing the forest, such as biodiversity, production, outdoor life and other social benefits - all needs to be included in a "balancing act in priority", says Rummukainen. Photo: Private

The forest is not sufficient for it all

Markku Rummukainen does not want to be pigeonholed when it comes to the forest and climate issue. However, it is a fact that it is not possible to get everything from the forest, in every way, for everything that is important, and all at once, he says, and emphasises that the climate is not the only aspect to take into consideration, and perhaps is not what carries most weight either in every situation when we talk about the forest.

“The forest is a limited resource. It is not possible to simultaneously use it for maximal carbon sequestration and the greatest possible utilisation of biomass for substitution. Neither of those two extremes would necessarily provide optimal climate benefit either. Rather, it is a question of the balance that needs to be strived for. It may also be the case that other goals, such as biodiversity and social values, can carry just as much weight in decisions about the forest as climate benefits. Science cannot give a definitive answer about how you are to prioritise, but can however shed light on different options and their respective advantages and disadvantages, synergies, goal conflicts and uncertainties.”

The forest - a balancing act in prioritisation (PDF, 797 kB, new window)

Facts: The forest and the carbon cycle

The forest is a part of global carbon cycle. A growing forest takes up carbon dioxide through photosynthesis, and carbon is sequestered in trees, other biomass and the soil. The uptake in a stand of trees varies over its lifetime, but the resulting carbon sequestration can remain for a long period even after the forest has finished growing.

Extraction of biomass reduces carbon sequestration in the forest. How large the net effect of the extraction will be depends on how much of the biomass is removed, how the removed biomass is used and how fast new forest is established. When felling takes place there is also a net emission from the soil, in addition to the emissions linked to the extracted biomass.