The Ogasawara Islands (小笠原諸島) are an archipelago of over 30 subtropical islands some 1000 km directly south of central Tokyo, Japan. Administratively, they are a part of Tokyo. The islands are also known as the Bonin Islands, and the southernmost (uninhabited) group is known as the Volcano Islands.

The only inhabited islands are Chichi-jima (父島, lit. "Father Island") and Haha-jima (母島, "Mother Island"). Access to these islands is possible only via a single weekly overnight ferry from Tokyo, although there are plans to open an airport. Tourists are attracted to the islands by scuba diving and whale watching.

The uninhabited Iō-jima (硫黄島, "Sulphur Island"), better known in English as Iwo Jima, is a part of the Volcano Islands. Access to the island requires special permission.

Geology

The Ogaswara islands are a volcanic island arc. They lie at the junction of the Pacific Plate and the Philippine Plate. The Pacific Plate is subducting under the Philippine Plate, which creates an oceanic trench to the east of the islands. The islands were formed by volcanic activity caused by the subducting plate, and are composed mostly of an andesitic volcanic rock called Boninite, which is rich in magnesium oxide, chromium, and silicon dioxide. The basal rocks of the islands range from 65 to 1.8 million years old. The volcano on Iō-jima, Mount Suribachi, is believed extinct.

Most of the islands have steep shorelines, often with sea cliffs ranging from 50 to 100 meters in height. Several of the islands are fringed with coral reefs.

History

The first recorded settlement of the islands was an American colony founded in 1830, which persisted until the Second World War. Japan has ruled the islands since 1875.

Ogasawara subtropical moist forests

The Ogasawara Islands form a distinct subtropical moist broadleaf forest ecoregion, with a high degree of biodiversity and endemism. The islands are home to about 500 plant species, of which 43% are endemic. The forests are of three main types:

• Type I: Elaeocarpus-Ardisia mesic forest is found in the moist lowland areas with deep soils. The forests have a closed canopy with a height of about 15 meters, dominated by Ardisia sieboldii. Elaeocarpus photiniaefolius, Pisonia umbellifera, and Pouteria obovata are other important canopy species. These forests were almost completely destroyed by clearing for agriculture before 1945.

• Type II: Distylium-Raphiolepis -Shima dry forest is found in drier lowland and upland sites with shallower soils. It is also a closed-canopy forest, with a 4 to 8 meter canopy comprised mostly of Distylium lepidotum, Rhaphiolepis integerrima, Schima mertensiana, Pouteria obovata, and Syzgium buxifolium. The Type II forests can be further subdivided into:

• • Type IIa: Distylium-Schima dry forest occurs in cloudy upland areas with fine-textured soils. These forests contain many rare and endemic species, with Pandanus boninensis and Syzgium buxifolium as the predominant trees.

• • Type IIb: Raphiolepsis-Livistona dry forest is found in upland areas with few clouds and rocky soils. Rhaphiolepis integerrima is the dominant tree species, along with the fan palm Livistona chinensis var. bonensis, Pandanus boninensis and Ochrosia nakaiana.

• Type III: Distylium-Pouteria scrub forest is found on windy and dry mountain ridges and exposed sea cliffs. These forests have the highest species diversity on the islands. Distylium lepidotum and Pouteria obovata are the dominant species, growing from .5 to 1.5 meters tall. Other common shrubs are Myrsine okabeana, Symplocos kawakamii, and Pittosporum parvifolium.

Two bird species are endemic to the islands, the Japanese wood-pigeon (Columba janthina) and the Vulnerable Bonin honeyeater (Apalopteron familiare).

External links

• Bonin Information Service
• Ogasawara subtropical moist forests (World Wildlife Fund)