23.10.2026 | Stephanie Kusma | WSL News
In the Solothurn Jura, European bison are to be reintroduced gradually and under close scientific supervision. Researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) have, amongst other things, investigated the impact the animals have had on tree regeneration and the forest trees within their enclosure – with surprising results.
- WSLresearchers have investigated the impact of a European bison herd on the forest trees within their enclosure.
- Since the bison have been living in the enclosure, fewer trees have been browsed by wild animals than before.
- During the two-and-a-half-year observation period, the bison stripped the bark from around ten per cent of the trees in the forest, but only a few by more than half their circumference.
To this day, the European bison (Bison bonasus) in Switzerland can only be found in enclosures. One such enclosure is situated in Sollmatt in the Solothurn Jura. The Wisent im Thal association intends to gradually reintroduce the small herd kept there into the wild.
At present, the herd lives in an enclosure covering around 100 hectares, consisting of woodland and meadows, which is open to visitors. WSL researchers are supporting the project with scientific studies – including surveys on public acceptance of the animals, as well as studies on the potential implications of the reintroduction for forestry.
Bark and young shoots ¶
WSL biologist Andrea Kupferschmid analysed how many trees in the forest the bison feed on, either by eating the bark or the young shoots. Experts refer to the latter as ‘browsing’. On the Sollmatt, before the bison arrived, roe deer and chamois were the ones browsing on the young trees. Both game species still enter and leave the enclosure, as wildlife cameras show – the fence is no obstacle to them. “Since the bison have been living in the enclosure, however, fewer trees have been browsed than before,” says Kupferschmid. The smaller game has apparently changed its feeding behaviour. “Why remains unclear,” says Kupferschmid.
Nevertheless, whilst the biologist counted fewer young trees that had been browsed overall, the extent of browsing damage was greater on the affected trees. According to the researcher, the reason is likely to be mechanical: bison have larger mouths than roe deer and chamois and therefore take larger bites. Furthermore, the proportion of beech trees that have been browsed has increased; it is unclear why.
Less browsing ¶
Browsing has therefore not increased since the bison arrived, which is why the researcher considers the animals’ impact on the forest regeneration to be economically sustainable: “The situation in this regard remains unchanged.” The same cannot be said of another behaviour that poses a problem for forest owners: bark stripping. This refers to the animals peeling the bark off trees in long strips and eating it.
“The resulting injuries can provide entry points for infections,” explains Kupferschmid. Although most trees do survive the bark-stripping, infections devalue the affected timber because they leave visible discolourations. According to the researcher, during the two-and-a-half-year observation period, the bison stripped the bark from around ten per cent of the trees in the forest. This is significantly more than before the bison arrived, as roe deer and chamois do not strip bark. Red deer, which also eat bark, are rare in the area.
Most of the trees stripped of their bark in the enclosure were slender, with a diameter of less than 12 centimetres at chest height. Beech, spruce and fir trees were stripped of their bark only very slightly, if at all. In only 10 per cent of the stripped trees, the bark damage affected more than half of their circumference.
Hardwood is popular with bisons ¶
“It may be that the higher-than-normal bison density in the Sollmatt influenced the extent of the bark-stripping activity,” says Kupferschmid. After all, there are significantly more bison per hectare in the enclosure than in natural populations. The bison there were particularly fond of eating the bark of thinner-stemmed specimens of hardwoods such as sycamore, elm, ash and service tree. They largely spurned conifers and older sycamores with thicker bark.
This could become a problem if there were a lot of valuable timber in the forest, according to the researcher. That is not the case in Sollmatt, where most of the timber is used for firewood. “However, some of the tree species favoured by the animals in the Solothurn Jura are those that could become particularly important under future climate conditions, as they are better adapted to warmer and drier conditions,” says Kupferschmid. “That is why we should continue to monitor the animals’ impact on these species.”
Contact ¶
Publications ¶
Copyright ¶
WSL and SLF provide image and sound material free of charge for use in the context of press contributions in connection with this media release. The transfer of this material to image, sound and/or video databases and the sale of the material by third parties are not permitted.