The variety of animal and plant species on Jeju is also an important reason for its value as a natural reserve. Half of all Korean vascular plants grow naturally on the island while another 200 species of plants indigenous to Korea have been transported here. However, half of these species face extinction. The polar plants which came from the south during a glacial period and inhabit the peak of Jeju is one example. Other plants in the subtropical forest and lower regions of the island are also endangered.