Swiss forests struggle with the next generation

In Switzerland's forests, trees mostly reproduce naturally via seeds. This natural regeneration is a guiding principle of forestry, ensuring that trees are always adapted to their environment. However, the damage caused over the last 25 years by winter storms, drought and bark beetles shows how vulnerable our forests are to extreme events. According to climate scenarios, these will become more frequent in the coming decades.

On the other hand, the gaps left by these storms offer an opportunity for natural forest regeneration. This is demonstrated by the National Forest Inventory (NFI) conducted by the WSL: on the northern side of the Alps, the number of young trees per hectare increased significantly after the winter storms Vivian and Lothar. However, in the Central Alps, the number of regrowing trees declined – on the one hand because young trees lack light in overmature forests, and on the other because in some regions there are many wild ungulates that damage trees. 

Forests in transition 

Forests in low-lying areas and in the mountains also differ greatly. In the lowlands, drought and bark beetles are decimating the economically important spruce, while climate-fit tree species are not yet available everywhere. In the mountains, where the forest plays a vital role in protecting against natural hazards, stands that are too old reduce the protective effect in the long term.

Promoting young trees of climate-adapted species is therefore a key task for foresters. For this reason, the WSL is conducting various research projects on this topic, the findings of which are now being presented in a special issue of the Swiss Journal of Forestry (SZF). The researchers are reviewing and updating the recommendations that emerged in 2016 from the research programme "Forests in Climate Change". This is because not only the pressures on forests have increased since then, but also the demands placed on them, such as storing carbon and promoting biodiversity.

The articles in the special issue of the SFZ present these and other results of WSL research in detail (in German): 

• Mountain forest experts present a questionnaire that helps to set priorities for the management of protective forests. (Zürcher et al.)
• Data from the National Forest Inventory (LFI) show that many young beech trees have been able to regrow at low altitudes thanks to the gaps left by storms and bark beetles. At high altitudes, however, there is often a lack of young forest. (Wohlgemuth et al.)
• As part of the long-term WSL project on mountain forest regeneration, varying numbers of trees have been felled on ten test sites in dark mountain forests since 2020 to see how young trees regrow after silvicultural interventions. (Nikolova et al.)
• Between 2020 and 2023, WSL staff planted 56 test plantations with a total of 55,000 young trees throughout Switzerland. Initial findings show that tree species that will be perfectly suited to higher temperatures in the future are already able to grow at higher altitudes today. (Schwarz & Streit)
• Since 2021, researchers have been testing young trees of six tree species in plastic tunnels at artificially elevated temperatures on three test sites. After four years, it is clear that all tested tree species grow well in deep soils, but that Douglas fir, which originates from North America, thrives best in shallow soils that are prone to drying out. (Moser et al.)
• Changes can also be observed well on the basis of old cultivation experiments. The WSL collects such findings in the " Dokutool Zukunftsbaumarten " (Glatthorn et al.).

Contact: 

Barbara Moser, Tom Wohlgemuth and Petia Nikolova edited the special issue and are available for media enquiries.