We know, because they teach us at school since we are small, that the trees on a slope protect what is downstream from landslides, avalanches and various landslides. And logic tells us that not all trees are equally effective: it is clear that, for example, a taller and bigger tree is more effective than a newborn one.
To really protect yourself from natural disasters, however, common sense is not enough: that’s why a study published on Cold Regions Science and Technology He explains, after fifty years of observations and data collection, what differences there are between tree and tree when it comes to slowing down or stopping avalanches – how old they must be effective, for example, and which species “work” better.
Fifty years of avalanches. The project, which celebrates its fiftieth anniversary in these days, has been carried out by the WSL – Institute for the study of snow and avalanches, on the slope of Stillberg, in the Val Distchma, in Switzerland, near the architect locality of Davos.
Here, at an altitude between 2,000 and 2,230 meters, the north-east slope has been subjected, starting from 1975, to a firning intervention, which is different from the reforestation and plans to bring the forest where it has been absent for at least 50 years (or where it has never been).
The trees were planted just above the limit of the woods: these are about 92,000 specimens of Cembri, Larici and Mughi, which were then monitored in the following fifty years to study their interactions with the avalanches that come from the upper altitudes.
There is talk of a total of 214 avalanches observed, most of which are concentrated between 1975 and the beginning of the nineties. Then something happened to the forest and the avalanches began to arrive less and less on the valley.
Not all trees are the same. What happened is that the trees grew: when they exceed twice the height of the snow mantle from which the avalanches come off, they become an effective barrier, while first they risk being overwhelmed and overcome by the snow.
There are also differences according to the species: the evergreen conifers (Mughi and Cembri, in this case) retain the snow better than the deciduous ones (like the larches), because their hair is always present during the year. A larch forest, therefore, is less effective as a shield against avalanches than one of Cembri or Mughi pines.
Although limited to certain species and a specific geographical area, the results of the study are important for any afflorer project, in particular those aimed at protecting a side from the avalanches. Or in simpler terms: not all trees are the same, and if you want to bring the forest where there was no one, you have to take these differences into account to plan an effective one.
