The high Mediterranean mountains above 1700 metres presents some special characteristics. Winters are very harsh and long; the thickness of the snow and strong frosts prevent almost any type of biological activity. Once the snow has disappeared, the soil dries quickly due to the strong sun and high temperatures reached in summer. The period of time suitable for the growth of vegetation is therefore very short and for the above-mentioned reasons, the land is dry most of the time. Under such conditions, the forest enters a state of crisis, being replaced by "piornales" (ciste and broom formations) and thickets "pluvinulares" accompanied at lower levels by Scots pine, often isolated individuals twisted and deformed by the snow.