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Forests bind lots of CO2. As a renewable resource, wood is climate-friendly. But how should forests in Switzerland be tended and the wood be used to ensure the best climate protection?

A large beech tree removes up to eight tonnes of CO2 from the atmosphere during its lifetime, storing the carbon in its stem, roots and branches. According to calculations published by Esther Thürig, head of the ‘Resource Analysis’ Research Group at WSL, her team and other colleagues from consultancy offices and universities, around 925 million tonnes of CO2 are stored in Swiss forests. Half of this CO2 is stored in the forest soil, and the other half in the trees. This CO2 reservoir is equivalent to almost twenty times Switzerland’s annual CO2 emissions. There is clearly a need for more forest. Larger areas of forest lead to less CO2 in the air – which means that emissions can be cleverly offset.


In Switzerland, however, there is hardly any room for more forests – except in the Alps. The question is therefore much more whether and how the existing forests can bind more carbon. Currently more wood is growing in Swiss forests than is harvested – especially in the Alps, where harvesting timber is costly and economically unattractive. But as Esther, who is a biologist, warns: “The forest does not always serve as a sink for carbon. It can also become a source!” For example, when storms like Lothar sweep across the country, trees are uprooted or blown down. They then rot and release CO2 in the process. The same applies when trees die due to drought or bark beetle infestation or burn in a forest fire. With climate change, such events are expected to become more frequent.

Wood used for construction stores carbon

Moreover, from the point of view of forest management, where the forest edge is the system boundary, every tree stem that is removed from the forest reduces the carbon stock in the forest – regardless of whether it was harvested regularly or blown down in a storm, and regardless of how the wood is used after­wards. This does not mean, however, that CO2 is actually released into the air. If the wood is used in furniture or buildings instead of more energy-intensive materials such as concrete, the carbon remains bound in the wood. It therefore makes most sense to investigate the effects of forestry and the timber industry in combination.

This is what Esther Thürig and her colleagues have done: they considered a total of five scenarios, i.e. possible future developments, and calculated their impact on Switzerland’s carbon balance. The range of possible ‘futures’ extends from increased use of wood for building and heating, through the continuation of current trends, to significantly fewer trees being felled than today. “It may come as a surprise at first glance,” Esther comments, “but letting as many large old trees as possible grow is not the best way to protect the climate in the long term.” The further into the future you look, the clearer it becomes that the scenario with intensified but still sustainable use of wood binds the most carbon. To express this a bit more precisely: in order to extract as much CO2 from the atmosphere as possible in the long term, forests should be managed to produce more wood than they do today. And the indigenous wood they produce should be used in building. When a wooden building comes to the end of its life, the wood it is made of should be burned and the heat used. When wood is used like this, it contributes to climate protection in various ways. It not only creates a larger CO2 reservoir, but it also replaces energy-intensive building materials before the wood in the old building is used as a substitute for fossil fuel. This could, in the long term, reduce the annual CO2 emissions of Switzerland by around five percent.

This scenario cannot, however, be implemented at the push of a button. Since the economic viability of exploiting the forest has deteriorated (see page 3), it is not the case that more wood is currently being harvested – so it is not possible to use more wood for construction. The problem is aggravated by the fact that Swiss forests will, in future, supply increasingly less spruce wood because spruce trees are poorly adapted to the predicted future climatic conditions. The wood from the deciduous trees that grow in their place has rather different material properties. Neither sawmills nor carpenters can process it so well and at such a cost-covering level as today’s spruce timber.

Promoting carbon sinks

Esther is currently updating the scenarios to take into account, in particular, the current situation and the latest research findings from the simulation models. It is especially important to know how the carbon balance will be affected if things go on in the same way and current trends continue, for example if the price of wood continues to fall. This is the basis for comparisons to assess whether and how well climate protection measures work. Both forestry and the timber industries are trying to process the sink performance of their particular subsystems. For example, private individuals or companies can purchase CO2 certificates from the ‘Oberallmeindkorporation Schwyz’ to voluntarily offset their emissions. In return, the corporation is increasing wood production in its forests in a controlled and sustainable manner.

A year ago, forest owners and forest managers also founded the association ‘Wald-Klimaschutz Schweiz’ (‘Forest Climate Protection Switzerland’). This association aims to help its members sell the service their forests provides as carbon sinks on the CO2 markets.  Switzerland is, after all, meeting a considerable proportion of its international commitment to reduce CO2 through its forests. The additional revenues could help to steer management even more specifically towards climate protection. The timber industry is pursuing similar objectives and has founded its own association ‘Verein Senke Schweizer Holz’ (‘Swiss Wood Sink’) in the hope of obtaining some of the money from the CO2 compensation funds through promoting the use of wood and binding more carbon in the wood it uses.

The scenarios and models developed by Esther and her colleagues provide valuable information for developing effective compensation payments or subsidies. They also help to improve the accuracy of Switzerland’s greenhouse-gas reporting for the international community.
(Birgit Ottmer, Diagonal 1/20)


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