Study: "Diverse forest" is more stable

The Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and its Institute for Snow and Avalanche Research (SLF) studied what type of forest offers the best protection against hazards such as landslides. "The most diverse structures possible in the forest - both below and above ground - provide the best protection against landslides," the study leaders share in a recent press release.

New findings

Landslides and hillslope debris flows are mainly triggered by rain. Due to climate change and an expected increase in heavy precipitation, "shallow landslides and hillslope debris flows are likely to occur more frequently," the release states. The latest findings on the effect of forests on landslides are now summarized by several researchers in a special issue of the Switzerland. Journal of Forestry (SZF) together. What stands out is how important the condition of the forest is:

Very dense forests and windthrow areas protect less well against landslides than those with a stepped stand structure. On very steep slopes, however, forests reach their limits: On slopes steeper than 38°, there are even more landslides per area in forests than in open areas. Forests on very steep slopes are usually less maintained and are mainly located in higher and more inhospitable areas, where spruce, which is susceptible to disturbance (windthrow and bark beetles), is also particularly prevalent. Spruce trees do not have deep roots and are therefore easily carried away on steep slopes.

Researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL and the WSL Institute for Snow and Avalanche Research SLF have demonstrated which type of forest provides the best protection using large-scale data sets on vegetation and natural events. They show that reforestation and natural disturbances, such as hurricane Lothar, which will mark its 20th anniversary in December, but also the skillful management of the forest can significantly influence its protective function against landslides.

"The most diverse structures possible in the forest - both below and above ground - provide the best protection against landslides," says Christian Rickli of the research team. This includes a good mix of different tree species as well as a diverse age structure of the trees.

For their investigations, the WSL researchers drew on information from their landslide database. Since 1997, data on more than 750 landslides have been recorded in this database. This information is now also available online available, but access is required for this.