| OCR Text |
Show caused by the ram- effect of tree trunks carried down with the slide. The four tree species which occur in our mountain areas are of ( have their) specific meaning for avalanche mapping. For example: avalanches seldom occur in areas forested with dense, large and old stands of spruce ( Picea excelsa), cembra pine ( Pinus cembra) and mountain pine ( Pinus montana). On the other hand, caution must be exercised with scattered small stands or small strips of these species remaining on ridges. They convey the impression of being a closed barrier, which is, however, easily swept through by avalanches without causing any damage to the stands. In summer, a deceptive picture is projected by the shrub- like form of the mountain pine or dwarf-pine. The dense and tall shrubs give the impression of constituting an effective barrier against the release of slides. Such stands are pressed to the ground in winter. Dwarf- pines escape damage even when swept by large avalanches. The larch ( Larix decidua) is very resistant to slides because of its tough wood, its strong roots and its 1imberness in the sapling state. Trees ten meters tall can be bent to the ground and be overrun without breaking. Such trees will regain their erect position after the weight has been lifted. Similar observations can be made about resistance to creep and glide of the total snow cover. An open and old stand of larch can be swept by large avalanches without being damaged. More confusion is added by the fact that in summer, these trees have needles and give the impression of a closed stand, which is not true for winter when the needles are shed. A forest is often scarred by avalanches. Stands of young trees of the same age which grow on the edge of the avalanche path indicate that avalanches occasionally occupy a much wider path. Trees without branches could have been growing at one time in the path of an avalanche. Remains of forests swept or carried down by avalanches can be used for avalanche mapping long after the snow has melted. These scars often show the extent of an avalanche better than the snow that has been carried down, since new snowfall and wind can obscure the latter. The forest is of additional importance with respect to construction, which becomes apparent only with the development of the avalanche zoning plan. Forested areas fall under different legal regulations. To build in the forest requires the clearing of a wooded area. Even if the building enthusiast could use an open area within a forest, it would be the equivalent of clearing, as is true of any claim to forest lots which become temporarily or permanently changed. Since foresters and community authorities of certain cantons may have no knowledge of this definite federal regulation, all mountain forests should be declared off- limits for construction and mapped in red. We know of avalanche evidence which the layman would not consider possible. The large " Breitzug" avalanche that swept down in the area of Davos on January 26, 1968, dislocated rocks with a diameter of up to 1.6m. The rocks were picked up from the bed of the " Landwasser" and carried over a distance of 66m with an altitude difference of 14m up the opposite slope. The slope was covered with fist- and head- sized stones. A rock 9m long and 4m high can be found on the old Susten road, 500m behind the village of Obermad. An attached plate contains the following inscription: |
