The SLF began researching protection forests in the 1950s. In the wake of the extreme winter of 1951 (Fig. 1), when numerous avalanches were released on wooded slopes, major endeavours were initiated to re-establish forests on the affected sites. The SLF monitored a variety of these afforestation projects and examined their influence on both the snowpack and avalanche activity.
Among these projects, the most well-known planting scheme, encompassing around 92,000 trees, was implemented at the Stillberg test site in the Dischma valley near Davos (Fig. 2). Upon its completion, a variety of scientists engaged in extensive research with a focus on significant practical relevance to mountain foresters. They concentrated on the ecology and afforestation of species at the tree line. This was the first major collaboration between the then EAFV (now WSL) and the SLF.
It was recognised at an early stage that forests not only support the snowpack with their tree trunks, but also influence its stability by way of their canopies. Against this backdrop, the SLF has increasingly turned its attention to existing forests and the role they play in protecting against avalanches as well. There was an upsurge of interest in this topic and in avalanche fractures in open forests (forest avalanches) in particular in the 1980s, when society became concerned about the decline of mountain forests. Forest avalanches were extensively monitored at the time (Fig. 3), and these investigations continue to serve the purpose of assessing the effectiveness of protection afforded by mountain forests. At the same time, the SLF was closely examining the interaction that takes place between forests and the snowpack. In Lusiwald forest near Davos-Laret, for instance, it was exploring the effect of the snowpack on young trees in subalpine spruce forests and assessing the relative appropriateness of various measures to regenerate such forests.
Reflecting changes in forests and the expectations associated with them in recent decades, the focus of research into avalanche protection forests has shifted as well. Following the substantial increase in forest cover in the mountains, planting campaigns are paying less attention to high altitudes than they were 60 years ago. The SLF is currently concentrating its research on the effects of climate change and natural disturbances, such as windthrow, on the effectiveness of protection provided by mountain forests (Fig. 4). Its scientists can now apply methods that were not available in the early days of research into avalanche protection forests at the SLF. These include the recording of forest structures by way of laser scanning, annual ring analyses, and computer simulations of forest-avalanche interactions. Nonetheless, the early projects conducted by the SLF remain among the most important fundamental resources for addressing current research questions. Researchers today are still using the Stillberg afforestation project to study the effects of climate change on the tree line, for example. They are also utilising the forest avalanche data collected in the 1980s (Fig. 3), together with more recent data resources, to improve both the modelling of avalanche dynamics and risk analyses relating to forests. In addition, good collaborative relationships with other snow and avalanche research disciplines at the SLF, and with the forest research activities of the WSL, are now more important than ever before.