From the satellite, a green spot characterizes unequivocally the northern part of Sicily: it is the area of the vast forests of Nebrodi mountains. The influence of the Tyrrhenian Sea on the norther slope of Nebrodi leads to the formation of a great humidity converging along the valleys, which maintains itself also thanks to the rich arboreal covering: these conditions have enabled the survival of particular vegetal and animal species after the Tertiary period.