Vegetation
Pascal Vittoz, Institute of Earth Surface Dynamics, FGSE
Given the significant relief and their vast extent, the Valais Alps exhibit a great diversity of habitats (Delarze et al., 2015) and species. Indeed, the Valais Alps span from 372 m (Leman shores) to 4,631 m (Dufourspitze), covering all vegetation zones. Additionally, they intersect three biogeographical regions.
Western Internal Alps: This region includes the Rhône Valley and the side valleys. It is characterized by a subcontinental climate, with high summer temperatures, cold winters, and low precipitation. In the foothill zone, the oak thickets have largely been replaced by vineyards. In the driest areas (rocky zones), as well as in secondary positions, steppe meadows feature a floristic composition similar to that of Central European steppes (between Hungary and Mongolia). In the montane zone, xerophilous pine forests are natural, benefiting from dry conditions unsuitable for beech. Agriculture remains significant, with extensive meadows and pastures, and locally, medicinal plant cultivation. The pine forests are replaced in the subalpine zone by spruce forests, followed by larch and Swiss stone pine forests, which mark the forest boundary. However, these forests have often been replaced by pastures or heathland dominated by rhododendrons. Above this, the alpine zone is predominantly occupied by alpine meadows, interspersed with large areas of scree and rocks. The geological diversity of the Alps allows for the presence of all alpine habitats found in Switzerland (dry limestone meadows, fresh limestone meadows, ridge grasslands, acidic rocky meadows, acidic meadows of the upper alpine zone, snow basins, etc.). Finally, the nival zone is highly present, with vegetation limited to isolated plants in the most favorable situations, with a record at 4,507 m (Saxifraga oppositifolia on the Dom).
Northern Slopes of the Alps: This region includes the Chablais, between St-Gingolph and the Grand St-Bernard Pass, and is characterized by cooler temperatures and significant precipitation. In the foothill zone, forests are dominated by beech forests, which are interspersed with anthropized environments (meadows, fields), with lime and ash groves on the steep slopes. In the montane zone, beech and fir trees take over, but are often dominated by spruce, which is preferred by foresters. Agriculture remains locally significant with meadows and pastures. Spruce forests dominate the subalpine zone, forming the forest boundary, although they have often been replaced by pastures, alder groves, or rhododendron heathland. The alpine and nival zones are similar to those in the internal Alps, with a dominance of limestone rocks to the north of Martigny and siliceous rocks to the south.
Southern Slopes of the Alps: This region is quite small, covering only the southern slopes of the Simplon (Simplon-Dorf, Gondo). The temperatures are mild, but precipitation is very high throughout the year. The entire region is dominated by siliceous rocks. The montane zone is covered by acidophilic beech forests, which give way to spruce forests in the subalpine zone, with spruce accompanied by larch at the upper forest limit. Agriculture is now very marginal in this region. The alpine and nival zones are similar to those in the internal Alps, but only acidophilic environments are represented.
