In the Jura Mountains, the strong, cold winds propel ice crystals which can traumatize the spruce twigs emerging from the protective snowpack. Their implantation in spruce forests limits this risk. They must be sufficiently cleared so that the trees, less crowded, have more assimilating surface and can develop rectilinear trunks of greater volume. If they are too dense, the poorly lit basal branches will prune naturally and the foliage will rise to better lit but much further from the ground areas.