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Diversified Environment on the Amami Islands The islands are divided into two types according to their geological nature: high islands, which are somewhat mountainous, and low islands, which generally consist of raised coral reefs. Subtropical rainforests and mangrove forests develop on high islands, while built- up coral terraces and limestone karst landscapes can be found over large parts of the low islands. Subtropical coastal vegetation develops on all of the low islands, and coral reefs grow in the surrounding sea. Although Amami Islands are a group of small islands, it possesses a variety of environmental factors that form different types of subtropical landscapes. Furthermore, these differ from island to island, resulting in various types of natural environments that provide unique habitats to a number of endemic or threatened species. Mangrove forests A mangrove forest exists at the estuary of Sumiyou River on Amami Oshima. Although the forests are not large in scale, species diversity is considered high and a number of threatened species can be found. Raised coral reef terrace Subtropical rainforests Hyakunodai terrace on Kikaijima rises 2mm a year in average, making it one of the fastest rising landmasses in the world. The terrace appears to have been at sea level around 120,000 to 130,000 years ago. It has become an important subject in the world, especially in regard to climate change in light of recent scientific research. Rainforests, which are rarely found in subtropical zones, develop due to the area's high rainfall associated with frequent monsoons. The rainforests in Amami Is. provide habitats for many endemic species. Tropical coastal forests Tropical plants, including Cycas revoluta, Pandanus tectorius, Scaevola furtescens, Ficus microcarpa and Ficus superba var. japonica, are often found on the coastal area. These plants are intimately associated with the lifestyle of the indigenous Amami people. Limestone karst Many limestone caves have developed on the low islands, originating from raised coral reefs. Of note among these, Okinoerabu Island has about 150 caves in an area comprising less than only 100 km2 . Coral reefs While coral reefs are found on all of the Amami Islands, the better - established reefs can be found on those islands that are more directly influenced by the Kuroshio Current. About 220 species of corals exist through the entire islands area.