The Nature Reserve includes the Tuscan part of the upper Tiber basin; it has an area of 470 hectares, while its altitude goes from about 850 meters to the 1,234 meters of Mt. Nero summit. On the whole, the area is inaccessible and characterized by great naturalistic values, while the human presence is rather limited. The Reserve is almost entirely covered with woods (above all beech trees), even if there are also some rocky environments and screes, as well as grasslands and shrubs contributing to considerably increase the biodiversity of this protected area. The forests, besides being very rich in flora, are also very rich in big-size trees, an evident sign of the scarce impact of man in the latest decades.