Alneto

The Green Alder (Alnus viridis) forms dense thickets (alder woods) in the catchment areas and on the slopes where the water table flows shallow and the soil is very humid, often with surface water emergence and runoff. Its distribution area can be related to that of larch and red fir at the boundary with high-altitude meadows; however, the alder wood does not evolve into a forest but accompanies and replaces it where the excessive soil moisture prevents the development of coniferous trees. Depending on the environmental conditions of the area in which it grows, the Green Alder can reach a height of 3 meters.

A Pioneer

The Green Alder is considered a pioneering plant thanks to its shallow root system, capable of colonizing and, at the same time, stabilizing slopes undergoing erosion. It is also able to resist certain types of avalanches due to the poor resistance offered by its deciduous, prostrate, and flexible branches that bend without breaking when covered with snow. At the same time, in winter, mountain dwellers feared slopes characterized by the presence of alder wood where the detachment of avalanches was more likely due to the sliding plane created by the green alder branches. Moreover, on poor soils, it significantly contributes to increasing soil fertility through a process of fixing atmospheric nitrogen. This process takes place in the plant's roots where, hosted in special nodules, nitrogen-fixing microorganisms (actinomycetes) mineralize gaseous nitrogen and release it to the host plant and the surrounding environment.

Other Plants

The soil colonized by alder woods hosts a particular herbaceous flora whose components are often referred to as megaforbs or "tall nitrophilic herbs." These are very demanding and large species that, being able to live in water-soaked soils, encounter no other limiting factor for their development other than light. They produce tall stems and leaves, rather tender, supported mainly by the turgor of tissues rich in water: a typical example is the Alpine Bear's Ear (Adenostyles alliariae). Other less conspicuous tall herbs include aconites (Aconitum napellus, Aconitum vulparia), Masterwort (Peucedanum ostruthium), sorrels (Rumex sp.), Villars' Gentian (Gentiana villarsi), Wood Cranesbill (Geranium sylvaticum). Underneath these, smaller plants develop such as the twoflower violet, round-leaved saxifrage, and Hepatica nobilis.

Fauna in the Alder Wood

In the summer, the areas occupied by alder woods, alternating with more open spaces of larch forests and meadows, provide excellent shelter for ungulates that willingly frequent these habitats to feed. For the same reason, the foliage of the Green Alder offers refuge from predators to male Capercaille during the molting season when flying is more difficult, while the young find abundant food and easy hiding places under the large leaves of the herbs that grow in the shade of the alders. The dense cover of the alder wood allows almost exclusive development of fast-growing shade-tolerant herbs with broad leaf blades. These, in turn, ensure the maintenance of a good degree of soil moisture, appreciated by the small, more hygrophilic soil fauna, such as various species of springtails or ground beetles, like Trichotichnus laevicollis, chiefly feeding on seeds, and Oreonebria castanea, a species normally characteristic of the perinival zones, which in the northern Cottian Alps prefers lower altitudes, concentrating in shady and cold concave valleys or channels, under the alder shade. During winter, the alder branches bend under the weight of the snow, providing clear ground surfaces and a sheltered space from harsh weather conditions due to its insulating properties. This facilitates the survival of small mammals such as the snow vole (Chionomys syriacus). Finally, between the snow and branches, Capercailles find favorable conditions to build igloos where they take refuge in the cold season.

The Alder Wood in the Cozie Alps Parks

The alder wood is a fairly common habitat in the mountain territories managed by the Protected Areas of the Cozie Alps. Especially on the north-facing slopes of the Natural Parks of Val Troncea, Orsiera Rocciavré, and Gran Bosco di Salbertrand where they occupy the altitudinal band between forests and pastures. The progressive abandonment of traditional activities such as pastoralism causes an expansion of this type of vegetation.