These conditions caused great diversity in species. It due to its diverse ecological condition is rich in relict species that some of them referred to the Tertiary period. It also contains superlative natural phenomena or areas of exceptional natural beauty and aesthetic importance. It is also outstanding example representing significant ongoing ecological and biological processes in the evolution and development of terrestrial, ecosystems and communities of plants.
Hirkani forests of the Caspian Sea, was registered as world heritage in the United Nations Educational, Scientific and Cultural Organization. The Hirkani ecosystem is home to 296 species of birds, 98 species of mammals, and 150 native trees and bushes. These forests have different types of vegetation depending on the elevation. Its best-known trees are the rush, oak, alder, elm, ash, and cedar. It is outstanding examples in the record of significant on-going geological processes in the development of landforms and significant geomorphic or physiographic features.
