Sado, the largest island (857km^2) in the Japan Sea lying about 32 km off the coast of the mainland of Japan (Fig. 1), is located between 37°48′and ca. 38°N. Lat. and between ca. 180°and 138°34′E. Long. The island is composed of two parts : Osado and Kosado, connected by the graben-valley Kuninaka. Osado is traversed lengthwise by a mountain range whose chief peak is Kinpokusan (1,173m), where as Kosado is composed of undulating hills, as high as 500 to 600m in altitude. The island is washed by the warm current named the Japan Sea Current, and is favoured by an oceanic climate, so that its winter climate is warmer than the adjacent areas in Houshu. The direction of the prevailing winds is WNW in winter and ESE-SE-WSW in summer. The vegetation of the island, therefore, is under the control of heavy NW winds in winter. The author has observed the floristic composition and structure of the forest communities in the coastal part of Osado. Deciduous broad-leaved thickets occur frequently along the northern coast of Osado. They consist of Quercus dentata and Acer mono, 2 to 8m in height. We can find them near the sea-shore exposed to the heavy west wind prevailing in winter. Along the porthwest coast of Osado from Tassha at the south to Seki at the north, fragmentary remnants of the deciduous broad-leaved forest are seen. They are composed of Quercus dentata, Acer mono, etc. The deciduous broad-leaved forest consisting of Acer mono, Zelkova serrat and Pinus spp. is seen along the eastern coast of Osado. The Acer mono-Zelkova serrata forests are thought to preserve the climax aspect as seen from the structure and floristic composition, etc. Evergreen broad-leaved forests are also found at Aikawa and Futami in Osado. These sites are favoured by warmer temperatures and are protected against the heavy west wind in winter. The climax forest along the warmer coast of the island is one of evergreen broad-leaved forests, and, from the floristic composition, it belongs to the Machilus thunbergu-Polystichum polyblepharum association of Shiia sieboldi alliance characterized by species such as Neolistsea sericea, Fatsia japonica, Machilus thumbergu and Elaeagnus macrophylla.
