A forest ecosystem reserve was established in 1991, and comprises the World Heritage area and various adjacent blocks of land. Yakushima was inscribed on the World Heritage List in 1993. Several peaks are over 1,800m with mountain ridges over1,000m surrounding these central high peaks. Topography from coastline to the mountainous summits is extremely steep. Mean annual temperature is 20 C in coastal areas, decreasing to 15 C inland.
Air temperature can fall below zero in the mountain summit area and snowfall is common in winter.
Annual precipitation is very high, varying with altitude and aspect, from 4000mm along the coast to 10,000mm inland. Warm temperate broad leaved forest previously covered extensive areas of south Japan. This has largely been removed, due to high human population pressure, and the warm temperate forest trees in Yakushima are thus some of the few remaining in Japan. Of great significance to the area is the presence of indigenous Japanese cedar Cryptomeria japonica , known colloquially as 'sugi'. The flora is very diverse for such a small island, comprising more than 1900 species and subspecies.