The ecosystem of the Hirkan National Park, belongs to the Caspian Hyrcanian (Girkan) mixed forests ecoregion, an area of lush deciduous broadleaved lowland and montane forests (subtropical and temperate rainforests) that completely cover the Talysh Mountains and partially cover the Lankaran Lowland.

The variety of elevations, the abundant rainfall, and the presence of old growth forests give the park an unusual richness of biota.

This area preserves many endemic plants species, relicts of the Tertiary period which were not affected by Pliocene and Pleistocene glaciations.

oxycarpa), European ash (Fraxinus excelsior), European hornbeam (Carpinus betulus), Oriental hornbeam (Carpinus orientalis), Oriental beech (Fagus orientalis), Caucasian persimmon (Diospyros lotus), Caspian locust tree (Gleditsia caspica), Caucasian alder (Alnus subcordata), black alder (Alnus glutinosa subsp.

Shrub species occurring in the area include the poet's laurel (Danae racemosa), Hyrcanian holly (Ilex hyrcana), greenbrier (Smilax excelsa), common ivy (Hedera helix), etc.

Despite occasional sightings, it was not clear whether leopards had been extinct in Azerbaijan by the late 1990s until a species was caught on camera in March, 2007 in the Hirkan National Park.