Floristic overview...
The characteristic forest species of the subalpine belt are the Swiss stone pine and the mountain pine (rarer), the larch and the Norway spruce.
The typical woods of this vegetation belt have the tree line as their upper limit. Describing its climate is particularly difficult, because the climate and the altitudinal range of the alpine belt vary according to the position and the aspect of each individual mountain range.
The wood has the typical look of the taiga, with an undergrowth of scrub, shrubs, heathland dwarf shrubs and herbaceous species that complete its appearance.
The species of the subalpine belt have to live in very harsh climatic and soil conditions:
- the growing season is shorter, which forces faster growth rhythms;
- frosts and out-of-season temperature swings are more frequent, damaging the shoots and the developing cones, and consequently reducing the capacity to spread by seed;
- greater exposure to high-altitude winds, with a consequent increase in transpiration. Moreover, at the tree line, wind loaded with snow particles has a sandblasting effect on the plants;
- snow cover softens exposure to frost, but if it lasts for long periods it shortens the growing season and encourages fungal diseases;
- frozen ground, besides helping to shorten the growing season, can cause water imbalances known as “physiological drought” in the last days of winter. That is, when the air warms up and the plant wakes from its winter dormancy, but the roots, sunk in ground that is still frozen, cannot take up water, and so the plant suffers;
- precipitation varies a great deal depending on the aspect of the mountain ranges: generally there is more rainfall on the edges of the Alpine system, while the climate is drier and more continental in its interior;
- soil conditions, especially on the slopes, are particularly difficult: steep gradients, earth movements, greater erosion due to the winds and to the action of water on soils and rocks through freezing and thawing, etc.
The harsh living conditions can be seen just by looking at the plants. As altitude increases, in fact, the trees reach heights that are gradually lower than normal. In particular, in the last 200 m below the tree line, the reduction, which at first is more gradual (about 1 m for every 100 m of altitude), becomes much sharper (4-5 m for every 100 m of altitude).
Bibliography:
Bernetti G., 1995, Selvicoltura Speciale, Utet – Torino
Pignatti S., 1998, I Boschi d’Italia, Utet –Torino