The Tagus River is the common element of this area, acting as a natural border between Spain and Portugal. The natural characteristics are identical on both sides of the border, the main ones that favoured its declaration in 2000 being the state of conservation of riverbank forests with river canyons that prevent their use for agriculture, and the existence of numerous species of flora and fauna included in the Birds and Habitats Directive as well as habitats of Community interest. Nearly 80% of these areas are classified as Special Protection Areas for birds (SPAs).

The protected area consists mainly of the valleys of the rivers Tagus, Ponsul, Erges and Aravil, which are characterised by steep slopes covered with dense Mediterranean vegetation and frequent rocky outcrops, dominated by granite-spattered shale. The adjacent areas are flatter, and are covered with holm oaks, eucalyptus trees, cultivated areas (rainfed cereals and olive trees), pastures and sclerophyllous forests. The characteristics are similar to those of the International Douro, but here the Arribes are much smaller, with a wider river.

This mosaic of semi-natural habitats with little human intervention, mixed with pastures and areas of intensive agricultural and livestock use, together with increasingly organised hunting management, allows the existence of important populations of rock birds typical of Mediterranean forests that are among the most threatened in Europe, such as the Spanish Imperial Eagle and the Black Vulture. The steep slopes of the Tagus valley and its tributaries are home to black stork, eagle owl, Egyptian vulture, griffon vulture, Bonelli’s eagle, golden eagle and black wheatear.

On the Portuguese side, you can still find the Pin-tailed sandgrouse, a species that was thought to be extinct in Portugal.