Switzerland has set itself a goal that is as ambitious as it is necessary: net zero by 2050. One of the most important raw materials on the road to a climate-neutral future is wood. This renewable natural resource binds CO2 from the atmosphere as it grows. Both as a material and as an energy source, wood and its numerous components offer alternatives to fossil fuels and materials. It is therefore hardly surprising that many sectors of industry plan to rely more on wood in future, whether in construction, in textile manufacturing or even in sectors such as electronics, chemicals and pharmaceuticals.

Little is known, however, about how much wood is available for all these desired applications and in what form. In order to shed some light on the matter, researchers from Empa and WSL have now comprehensively analyzed all documented material flows of wood in Switzerland. Their study, which was recently published in the journal Industrial Ecology, was carried out as part of SCENE, a joint initiative of the ETH Domain (see box).

Extensive data for an accurate assessment

For their analysis, the researchers used data for the year 2020 from 21 different sources – a methodological challenge, as the figures in the various sources did not always match. Wood is a diverse raw material that can take many forms on its way from harvest to use, often differing in volume and moisture content: raw timber, sawn wood, wood chips, wood pulp for the paper industry and much more. Harmonizing the different material flows was therefore a Herculean task.

But the effort was worth it. “Comparable studies from abroad rely heavily on modeling. They have data on how much wood is harvested in the forest, and they use this to calculate the subsequent material flows,” explains Nadia Malinverno from Empa's Technology and Society laboratory, the lead author of the study. The Empa team, on the other hand, used “real” data almost throughout, from timber harvesting and import/export to processing, recycling and disposal. This results in a much more accurate picture – albeit not a perfect one, emphasizes Malinverno. “We have to thank our colleagues at WSL and the Federal Office for the Environment (FOEN) for the good data that is available in Switzerland,” adds co-author and Empa researcher Claudia Som.

Wood should stay wood for as long as possible

The conclusion: Switzerland still has considerable potential when it comes to sustainable use of wood. For example, the recycling rate for wood is just under eight percent, compared to around 70 percent for paper. What's more: “Of the five to seven million cubic meters of wood that we harvest in Switzerland every year, around 40 percent is used directly for energy – in other words, it is burned,” says Malinverno. The researchers agree that this is far from ideal. Because: “For wood to fulfill its function as a long-term CO2 sink, it should remain in the technosphere as a material for as long as possible,” explains Som.

The vision of the researchers and of the SCENE initiative is a so-called cascading use of wood. In this approach, a harvested tree would first be processed into the largest possible high-quality product – such as beams and boards for construction. This wood should then be (re-)used in this function for as long as possible. Only when reuse is no longer feasible would the wood be broken down into the next material stage, for example as smaller boards, wood chips or wood-based materials. It should only go into the furnace when it can no longer be used as a material.

This is just one possible example of a wood cascade. As part of SCENE, the researchers want to investigate in more detail which uses of wood make the most sense, both from an ecological and economic perspective. One of their goals is to take a closer look at selected material flows: In what form is wood present in a particular flow? Where exactly is it produced? How is it treated? And how else could it be used? Nadia Malinverno, Claudia Som and their fellow researchers will be looking into these questions in the coming years.

Box: SCENE – a Joint Initiative of the ETH Domain
The Swiss Center of Excellence on Net-Zero Emissions (SCENE) is a joint initiative of all six institutions of the ETH Domain, which is partly funded by the ETH Board. Together, the partners conduct interdisciplinary research to support Switzerland in achieving the net zero target by 2050. The two Empa laboratories Technology and Society and Cellulose and Wood Materials are working together with PSI and WSL in the work package Biomass Carbon Cycle.
www.scene-project.ch

Comprehensive material flow analysis: Making the most of Switzerland's wood