Download p.3. Diversified Environment on the Amami Islands

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.