The Parc National des Cévennes is spread over a territory with an extremely low population density (about 10 inhabitants per square kilometre), due to a massive exodus of the population started during the first world war, and in a slow phase of recovery only since the ’90s. The natural environments are extremely diversified: the high Cévennes, a southern offshoot of the Massif Central, are characterized by granite outcrops which are scarcely erodible. On the other hand, the low valleys are formed by softer schist and by narrow cut out valleys. The woods are constantly expanding, with a strong presence of chestnut trees, still cultivated for the production of chestnuts. In 1985, Cévennes were declared UNESCO World Biosphere Reserve.