According to UNESCO, Hyrcanian forests form a unique forested massif that stretches 850 km along the southern coast of the Caspian Sea. The history of these broad-leaved Hyrcani forests dates back 25 to 50 million years, when they covered most of this Northern Temperate region. 

The announcement was made by the UN Educational, Scientific, and Cultural Organization on July 5 in Baku, where the World Heritage Committee met on 5 July 2019. In making the announcement, UNESCO said the “floristic biodiversity” of the ancient Hyrcanian forests in the north of Iran is “remarkable.” As well as are home to the Persian Leopard, nearly 57 other mammal species, and 180 bird species.

Iran has 22 cultural sites and 2 natural site inscribed by UNESCO Organization. Among them the Jewel of first Persian Empire, Persepolis has the global fame. And recently the HYRCANIAN forest is added.
2 natural sites, one in Iran and the other one at China were inscribed as World Heritage Sites by UNESCO on 5 July 2019.
The Caspian Hyrcanian mixed forests cover the northern slope of Alborz mountain, about 55,000 square kilometers near the southern shores of Caspian Sea of Iran and Azerbaijan. The forests contains the temperate broadleaves in a lush lowland with very rich ecosystems due to the particular orographic and climatic situation (precipitation rich, warm-temperate, high moisture from the Caspian Sea and damming effect of the Alborz mountain range). It covers parts of five provinces of Iran from east to west.
This forest is one of the major glacial refugia arcto-tertiary forest vegetation where a number of tertiary relics survived the Ice Age and developed numerous endemic taxa of flora and fauna. The nomination of the Hyrcanian Forests as a UNESCO World Heritage site had been under attention since 2001 prior to become the recent focus and one of the priorities of the Iranian government on 2017.

32.7 percent of volume of Hyrcanian forest is of Oriental Beech. A main feature of the region is the lack of conifers; only relics of coniferous species are present, which include European yew, Junipers, Mediterranean Cypress and Chinese Arborvitae.
The Caspian Sea coastal plains were once covered by Chestnut-leaved Oak, European Box, Black Alder, Caucasian Alder, Caspian Poplar and Caucasian Wingnut, but these forests have been almost entirely converted to urban and agricultural land.

The Caspian tiger once roamed these mountains, but is now extinct. Other large mammals here are the Caucasus leopard, lynx, brown bear, wild boar , wolf, golden jackal, jungle cat, badger, and otter.
This ecoregion is an important resting area for birds migrating between Russia and Africa and is thus a key habitat for many bird species. Some outstanding birds that can be found here are the greylag goose, white-fronted goose, Little bustard, glossy ibis , Eurasian spoonbill, night heron, red-breasted goose, peregrine falcon, Dalmatian pelican, Western cattle egret, squacco heron, greater flamingo, white-headed duck, and Caspian snowcock.