|1.||Geography||2.||.Geological history of the Amami Islands|
|3.||.Unique Biota of the Amami Islands||4.||Unique subtropical rainforests|
|5.||Diversified Environment of the Amami Islands||6.||Important endemic species of the Amami Islands|
|7.||People and nature of the Amami Islands||8.||International Recognition of Amami's Biodiversity|
The Amami Islands are located at the eastern edge of the Eurasian Continent. The Amami Islands extend 200 kilometers from north to south. They form part of the Nansei Islands, at the southwestern tip of the Japanese Archipelago. Made up of eight small inhabited islands, the Amami Islands have a total land area of 1,231 km2. The Kuroshio Current, one of the strongest warm ocean currents in the world, fl ows in the west of the Amamis, between the Eurasian Continent and the Amami Islands.
The Amami Islands are included in the Nansei (Shoto) Islands Chains and are located on the border between geographically the Eurasian Plate and the Philippine Sea Plate. The Nansei Islands were created as a result of the Okinawa Trough formation and tectonic shifting some 15 million years ago. The sea level has changed greatly over the past 1.7 million years, largely because of climatic variation, and the deposited Ryukyu limestone has built up along with the formation of the island chain's immense coral reefs. Due to repeated separation and reattachment to the Eurasian continent, two types of islands ultimately came into being: 'high islands', rich with hills and rivers, and 'low islands', formed of limestone that developed into coral reefs, and feature abundant groundwater.
About 15 million years ago, the Amami Islands were part of the Eurasian
continent, resulting in an overlap in the composition of terrestrial species.
When the islands were isolated from the Eurasia mainland by the sea, the
island biota also became separated from the continent and pursued an independent
evolutionary course. Therefore, many species of fl ora and fauna found
in the Nansei Islands, as well as the Amami Islands, are relicts of those
found on the Eurasian continent. The Kuroshio Current served as a barrier
separating the coastal area of the island chain from neighboring continents
and islands. This indicates that the biota unique to the coastal areas
of the Amami Islands have evolved independently.
The Nansei Islands have been likened to a "unique living museum" as they showcase the evolution of species on a continental island.
15 million years ago:
The present area of the Amami Islands once comprised the
eastern tip of a landmass extending from the southern part of Japan to Southeast Asia. It is thought that ancestral species of the Amami rabbit and Anderson's crocodile newt, as well as the Southeast Asian Ryukyu long-haired rat and Amami spiny rat were once found on the area.
Two million years ago :
The Okinawa trough began to sink greatly and the Inland sea (the present East China Sea) was terminated. This phenomenon gave rise to the Amami Islands. It appears that the flora and fauna expanding to the eastern tip of the continent before this era remained on the limited areas (high lands) and became isolated from the continent.
In general, subtropical zone are found between the warmth indexes of
180 and 240. Subtropical zone occur in those areas which are located between
a southern latitude of 20° to 30° and a northern latitude of 20° to 30°
on the high-latitude side of the tropical zone. Thesubtropical zone of
the world is comparable to the mid-latitude dry zone and rarely has rainforests.
Most areas of the subtropical zone are arid or covered in grassland.
Although the Amami Islands belong to a subtropical zone in terms of the warmth index, the islands have subtropical rainforests. This particular situation exists in only a few of the world's subtropical areas, such as in the high mountains of Central America, where monsoons bring heavy rainfall amounting to more than 2000mm a year. Forests similar to the cloud forests that usually appear at high altitudes exceeding 1000m in the tropical zone also exist in the mountaintop areas of Amami Oshima and Tokunoshima, namely Mt.Yuwandake (694m) and Mt.Inokawadake (645m).
*Warmth index: In general, monthly average of over 5°C is needed for plant growth. The Index puts basis on 5°C and it counts temperatures over 5°C and the Index is an annual total of monthly averages.
Distribution of temperature environment and rainfall
Plants of the World Vol.13, Asahihyakka
Modified from Ecological geography for plants (1977)
Pictorial by Mitsuru Hotta
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.
|High islands : Hilly island formed primarily of pre-Tertiary deposits and rock.|
|[ Amami Oshima(Is.) (712,33km2) ]
Extensive subtropical rainforests
Low islands : Flat island formed of limestone that was built up through the movement of coral reefs in the Quarternary Era.
|[ Yoron (Is.) (20.47km2) ]
Coral island surrounded by barrier reefs
|[ Okinoerabu (Is.) (93.65km2) ]
Karst island with many caves
|[ Kikaijima(Is.) (56.90km2) ]
Rising above sea level at a speed rarely observed in other regions of the world
*IUCN = International Union for Conservation of Nature and Natural Resources
Even now, among species common to Japan main land and the Nansei Islands, differentiation within species is taking place. This ongoing process continues to lead to the presence of subspecies endemic to the Amami Islands. For example, while the Japanese little horseshoe bat (Rhinolophus cornutus) is commonly found on the main Japanese archipelago and the Nansei Islands, those found in the Nansei Islands have diversifi ed into an endemic subspecies, Orii's least horseshoe bat (R. c. orii). Another example of a species that has differentiated in the Nansei Islands is Kuroiwa's ground gecko (Goniurosaurus kuroiwae kuroiwae), which is a relict endemic species in the Nansei Islands. This species has diversifi ed into fi ve subspecies within the Nansei Islands, including the Banded ground gecko (G. k. splendens), which is endemic to Tokunoshima.
As seen on the front cover of this brochure, the life of Amami islanders is closely associated with animals and plants. Islanders have been dependent on nature since early times. Natural resources are not only vital for their day-to-day life in regard to clothing, food and housing, but are also important for maintaining traditional local culture and industry.
The Amami Islands have been internationally recognized as an important
area for the preservation of the biodiversity, since the presence of coral
reefs that support a great number of taxa and other ecosystems provide
internationally endangered species as well as endemic species.
The Nansei Islands including the Amami Islands are considered globally significant in terms of conservation efforts for migratory species. Sea turtles and migratory birds use the islands to breed and also as a stopover point.