According to UNESCO, Hyrcanian Forest form a unique forested massif that stretches 850 km along the southern coast of the Caspian Sea. The history of these broad-leaved forests dates back 25 to 50 million years, when they covered most of this Northern Temperate region. These ancient forest areas retreated during the Quaternary glaciations and then expanded again as the climate became milder. Their floristic biodiversity is remarkable: 44% of the vascular plants known in Iran are found in the Hyrcanian region, which only covers 7% of the country. Hyrcanian Forest (also known as Caspian Forest), extends from the south of Azerbaijan to about 900 km to the east to the Iranian northern provinces of Gilan, Mazandaran and Golestan. This forest forms the outermost boundary of the west-Eurasian memorial deciduous forests to alpine thorn cushion corridors and forest-free dry vegetation of the Iranian highlands and Central Asia.
The Hyrcanian Forest cover the northern slope of the Alborz Mountain in Iran at the southern edge of the Caspian Sea and it contains very rich ecosystems due to the particular orographic and climatic situation. Hyrcanian forest contain the most important and significant natural habitats for conservation of biological diversity, including those containing threatened species of outstanding universal value from the point of view of science or conservation. It also contains superlative natural phenomena or areas of exceptional natural beauty and aesthetic importance. It is outstanding examples in the record of significant on-going geological processes in the development of landforms and significant geomorphic or physiographic features. It is also outstanding example representing significant ongoing ecological and biological processes in the evolution and development of terrestrial, ecosystems and communities of plants.
To date, 180 species of birds typical of broad-leaved temperate forests and 58 mammal species have been recorded, including the iconic Persian Leopard. The ecosystems of the property support populations of many forest birds and mammals of the Hyrcanian region which are significant on national, regional and global scales. To date, 180 species of birds typical of broadleaved temperate forests have been recorded in the Hyrcanian region including Steppe Eagle, European Turtle Dove, Eastern Imperial Eagle, European Roller, Semi-collared Flycatcher and Caspian Tit. Some 58 mammal species have been recorded across the region, including the iconic Persian Leopard and the threatened Wild Goat.