Article 2 of the World Heritage Convention defines 'natural heritage' as: natural features consisting of physical and biological formations or groups of such formations, which are of outstanding universal value from the aesthetic or scientific point of view; geological and physiographical formations and precisely delineated areas which constitute the habitat of threatened species of animals and plants of outstanding universal value from the point of view of science or conservation; natural sites or precisely delineated natural areas of outstanding universal value from the point of view of science, conservation or natural beauty.
The European Network of Biogenetic Reserves, founded in 1976, is designed to conserve representative examples of European natural heritage by developing a rigorous, systematic methodology. These biogenetic reserves may vary considerably in size, but their selection is generally based on two criteria: a) their value in terms of nature conservation: they must contain specimens of flora or fauna that are typical, unique, rare or endangered; and b) the effectiveness of their protective status: this must be sufficient to ensure the long-term conservation or management of a site according to the objectives set, as defined in Council of Europe Resolution (76) 17.