 One of the most significant are karst habitats which include submerged karst, such as Zrmanja and Krka canyons and tufa barriers, as well as underground habitats.The karst geology harbours approximately 7,000 caves and pits, some of which are the habitat of the only known aquatic cave vertebrate—the olm.Forests are also significantly present in the country, as they cover representing 44% of Croatian land surface.