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The Lesser Sunda Islands or nowadays known as Nusa Tenggara Islands ( id, Kepulauan Nusa Tenggara, formerly ) are an
archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands. Examples of archipelagos include: the Indonesian Arc ...
in
Maritime Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...
, north of Australia. Together with the
Greater Sunda Islands The Greater Sunda Islands ( Indonesian and Malay: ''Kepulauan Sunda Besar'') are four tropical islands situated within Indonesian Archipelago, in the Pacific Ocean. The islands, Borneo, Java, Sulawesi and Sumatra, are internationally recognised ...
to the west they make up the Sunda Islands. The islands are part of a
volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc lo ...
, the Sunda Arc, formed by subduction along the
Sunda Trench The Sunda Trench, earlier known as and sometimes still indicated as the Java Trench, is an oceanic trench located in the Indian Ocean near Sumatra, formed where the Australian- Capricorn plates subduct under a part of the Eurasian Plate. It is ...
in the Java Sea. A bit more than 20 million people live on the islands. Etymologically, Nusa Tenggara means "Southeast Islands" from the words of ''nusa'' which means 'island' from
Old Javanese language Old Javanese or Kawi is the oldest attested phase of the Javanese language. It was spoken in the eastern part of what is now Central Java and the whole of East Java, Indonesia. As a literary language, Kawi was used across Java and on the island ...
and ''tenggara'' means 'southeast'. The main Lesser Sunda Islands are, from west to east: Bali,
Lombok Lombok is an island in West Nusa Tenggara province, Indonesia. It forms part of the chain of the Lesser Sunda Islands, with the Lombok Strait separating it from Bali to the west and the Alas Strait between it and Sumbawa to the east. It is ...
,
Sumbawa Sumbawa is an Indonesian island, located in the middle of the Lesser Sunda Islands chain, with Lombok to the west, Flores to the east, and Sumba further to the southeast. Along with Lombok, it forms the province of West Nusa Tenggara, but th ...
, Flores, Sumba,
Savu Savu ( id, Sawu, also known as Sabu, Havu, and Hawu) is the largest of a group of three islands, situated midway between Sumba and Rote, west of Timor, in Indonesia's eastern province, East Nusa Tenggara. Ferries connect the islands to Waingapu ...
, Rote,
Timor Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, also ...
,
Atauro Atauro ( pt, Ilha de Ataúro, Tetum and Indonesian: ''Pulau Atauro'' or ''Ata'uro''), also known as Kambing Island ( id, Pulau Kambing), is an island and municipality ( pt, Município Ataúro, links=no, tet, Munisípiu Atauro, links=no or ...
, Alor archipelago,
Barat Daya Islands The Barat Daya Islands ( id, Kepulauan Barat Daya) are a group of islands in the Maluku province of Indonesia. The Indonesian phrase ''barat daya'' means 'south-west'. Geography These islands are located off the eastern end of East Timor. Wetar ...
, and
Tanimbar Islands The Tanimbar Islands, also called ''Timur Laut'', are a group of about 65 islands in the Maluku province of Indonesia. The largest and most central of the islands is Yamdena; others include Selaru to the southwest of Yamdena, Larat and Ford ...
.


Geology

The Lesser Sunda Islands consist of two geologically distinct archipelagos.Audley-Charles, M.G. (1987) "Dispersal of Gondwanaland: relevance to evolution of the Angiosperms" ''In'': Whitmore, T.C. (ed.) (1987) ''Biogeographical Evolution of the Malay Archipelago'' Oxford Monographs on Biogeography 4, Clarendon Press, Oxford, pp. 5–25, The northern archipelago, which includes Bali,
Lombok Lombok is an island in West Nusa Tenggara province, Indonesia. It forms part of the chain of the Lesser Sunda Islands, with the Lombok Strait separating it from Bali to the west and the Alas Strait between it and Sumbawa to the east. It is ...
,
Sumbawa Sumbawa is an Indonesian island, located in the middle of the Lesser Sunda Islands chain, with Lombok to the west, Flores to the east, and Sumba further to the southeast. Along with Lombok, it forms the province of West Nusa Tenggara, but th ...
, Flores and
Wetar Wetar is a tropical island which belongs to the Indonesian province of Maluku and is the largest island of the Maluku Barat Daya Islands (literally ''Southwest Islands'') of the Maluku Islands. It lies east of the Lesser Sunda Islands, which i ...
, is volcanic in origin. A number of these
volcano A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface. On Ear ...
es, like
Mount Rinjani Mount Rinjani ( id, Gunung Rinjani) is an active volcano in Indonesia on the island of Lombok. Administratively the mountain is in the Regency of North Lombok, West Nusa Tenggara ( Indonesian: ''Nusa Tenggara Barat'', NTB). It rises to , makin ...
on Lombok, are still active while others, such as Ilikedeka on Flores, are extinct. The northern archipelago began to be formed during the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Australian Australian(s) may refer to: Australia * Australia, a country * Australians, citizens of the Commonwealth of Australia ** European Australians ** Anglo-Celtic Australians, Australians descended principally from British colonists ** Aboriginal A ...
and the Asian plates. The islands of the southern archipelago, including Sumba,
Timor Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, also ...
and
Babar Babar ( ur, ), also variously spelled as Baber, Babur, and Babor is a male given name of Pashto, and Persian origin, and a popular male given name in Pakistan. It is generally taken in reference to the Persian ''babr'' (Persian: ببر), meaning ...
, are non-volcanic and appear to belong to the
Australian plate The Australian Plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately when India broke ...
. The geology and ecology of the northern archipelago share similar history, characteristics, and processes with the southern
Maluku Islands The Maluku Islands (; Indonesian: ''Kepulauan Maluku'') or the Moluccas () are an archipelago in the east of Indonesia. Tectonically they are located on the Halmahera Plate within the Molucca Sea Collision Zone. Geographically they are located ...
, which continue the same island arc to the east. There is a long history of geological study of these regions since Indonesian colonial times; however, the geological formation and progression is not fully understood, and theories of the geological evolution of the islands changed extensively during the last decades of the 20th century. Lying at the collision of two
tectonic plates Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...
, the Lesser Sunda Islands comprise some of the most geologically complex and active regions in the world. There are a number of volcanoes located on the Lesser Sunda Islands.


Ecology

The Lesser Sunda Islands differ from the large islands of
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
or Sumatra in consisting of many small islands, sometimes divided by deep
oceanic trench Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...
es. Movement of flora and fauna between islands is limited, leading to the evolution of a high rate of localized species, most famously the
Komodo dragon The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant ...
. As described by
Alfred Wallace Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution through natural se ...
in ''
The Malay Archipelago ''The Malay Archipelago'' is a book by the British naturalist Alfred Russel Wallace which chronicles his scientific exploration, during the eight-year period 1854 to 1862, of the southern portion of the Malay Archipelago including Malaysia, S ...
'', the
Wallace Line The Wallace Line or Wallace's Line is a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace and named by English biologist Thomas Henry Huxley that separates the biogeographical realms of Asia and Wallacea, a trans ...
passes between Bali and Lombok, along the deep waters of the
Lombok Strait The Lombok Strait ( id, Selat Lombok), is a strait connecting the Java Sea to the Indian Ocean, and is located between the islands of Bali and Lombok in Indonesia. The Gili Islands are on the Lombok side. Its narrowest point is at its southern ...
which formed a water barrier even when lower sea levels linked the now-separated islands and landmasses on either side. The islands east of the Lombok Strait are part of
Wallacea Wallacea is a biogeographical designation for a group of mainly Indonesian islands separated by deep-water straits from the Asian and Australian continental shelves. Wallacea includes Sulawesi, the largest island in the group, as well as ...
, and are thus characterised by a blend of wildlife of
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
n and
Australasia Australasia is a region that comprises Australia, New Zealand and some neighbouring islands in the Pacific Ocean. The term is used in a number of different contexts, including geopolitically, physiogeographically, philologically, and ecologi ...
n origin in this region. Asian species predominate in the Lesser Sundas: Weber's Line, which marks the boundary between the parts of Wallacea with mainly Asian and Australasian species respectively, runs to the east of the group. These islands have the driest climate in Indonesia, and tropical dry broadleaf forests are predominant, in contrast to the
tropical moist forests Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature. Description TSMF is generally found in large, discont ...
that prevail in most of Indonesia.


Ecoregions

The Lesser Sunda Islands are divided among six ecoregions: * The
Eastern Java-Bali rain forests Eastern may refer to: Transportation *China Eastern Airlines, a current Chinese airline based in Shanghai *Eastern Air, former name of Zambia Skyways *Eastern Air Lines, a defunct American airline that operated from 1926 to 1991 *Eastern Air Li ...
and Eastern Java-Bali montane rain forests cover Bali, which is the only of the Lesser Sunda Islands in the Indomalayan realm, and not part of Wallacea. Bali was once attached to the Asian continent (see Sundaland), and home to large Asiatic mammals like
Asian elephant The Asian elephant (''Elephas maximus''), also known as the Asiatic elephant, is the only living species of the genus ''Elephas'' and is distributed throughout the Indian subcontinent and Southeast Asia, from India in the west, Nepal in the no ...
s and the extinct
Bali tiger The Bali tiger was a '' Panthera tigris sondaica'' population on the Indonesian island of Bali which has been extinct since the 1950s. It was formerly regarded as a distinct tiger subspecies with the scientific name ''Panthera tigris balica' ...
. * The
Lesser Sundas deciduous forests The Lesser Sundas deciduous forests is a tropical dry forest ecoregion in Indonesia. The ecoregion includes the islands of Lombok, Sumbawa, Komodo, Flores, and Alor, along with the many adjacent smaller islands. Geography The ecoregion inc ...
include the northern chain of islands, from Lombok and Sumbawa east to Flores and Alor. The higher slopes of the islands contain forests of tall ''
Podocarpus ''Podocarpus'' () is a genus of conifers, the most numerous and widely distributed of the podocarp family, the Podocarpaceae. The name comes from Greek πούς (poús, “foot”) + καρπός (karpós, “fruit”). ''Podocarpus'' species ...
'' conifers and
Engelhardia ''Engelhardia'' is a genus of seven species of trees in the family Juglandaceae, native to southeast Asia from northern India east to Taiwan, Indonesia and the Philippines. The genus name is commonly misspelled "''Engelhardtia''", a "correctio ...
s with an undergrowth of lianas, epiphytes, and orchids such as '' Corybas'', '' Corymborkis'', and ''
Malaxis ''Malaxis'', commonly called adder's mouth, is a genus of terrestrial and semiepiphytic orchid Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colo ...
'' (adder's mouth), while the coastal plains were originally
savanna A savanna or savannah is a mixed woodland- grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...
grasses such as the savanna with
Borassus flabellifer ''Borassus flabellifer'', commonly known as doub palm, palmyra palm, tala or tal palm, toddy palm, wine palm or ice apple, is native to South Asia (especially in Bangladesh & South India) and Southeast Asia. It is reportedly naturalized in Socot ...
palm trees on the coasts of Komodo, Rincah and Flores. Although most of the vegetation on these islands is dry forest there are patches of rainforest on these islands too, especially in lowland areas and riverbanks on Komodo, and there is a particular area of dry thorny forest on the southeast coast of Lombok. Thorn trees used to be more common in coastal areas of the islands but have largely been cleared. These islands are home to unique species including seventeen endemic birds (of the 273 birds found on the islands). The endemic mammals are the endangered Flores shrew ''( Suncus mertensi)'', the vulnerable Komodo rat ''( Komodomys rintjanus)'', and Lombok flying fox ''( Pteropus lombocensis)'', Sunda long-eared bat ''(
Nyctophilus heran The Sunda long-eared bat (''Nyctophilus heran'') is a species of vesper bat. It is found only in Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans ...
)'' while the carnivorous Komodo dragon, which at three metres long and ninety kilograms in weight is the world's largest lizard, is found on Komodo, Rincah, Gili Motang, and the coast of northwestern Flores. * The
Sumba deciduous forests Sumba ( id, Pulau Sumba) is an island in eastern Indonesia. It is one of the Lesser Sunda Islands and is in the province of East Nusa Tenggara. Sumba has an area of , and the population was 779,049 at the 2020 Census; the official estimate as at ...
ecoregion includes Sumba. * The
Timor and Wetar deciduous forests The Timor and Wetar deciduous forests is a tropical dry forest ecoregion in Indonesia and East Timor. The ecoregion includes the islands of Timor, Wetar, Rote, Savu, and adjacent smaller islands. Geography Timor, Wetar, Rote, and Savu are pa ...
ecoregion includes Timor,
Wetar Wetar is a tropical island which belongs to the Indonesian province of Maluku and is the largest island of the Maluku Barat Daya Islands (literally ''Southwest Islands'') of the Maluku Islands. It lies east of the Lesser Sunda Islands, which i ...
, Rote, and
Savu Savu ( id, Sawu, also known as Sabu, Havu, and Hawu) is the largest of a group of three islands, situated midway between Sumba and Rote, west of Timor, in Indonesia's eastern province, East Nusa Tenggara. Ferries connect the islands to Waingapu ...
. * The more humid
Banda Sea Islands moist deciduous forests The Banda Sea Islands moist deciduous forests is a tropical moist forest ecoregion in Indonesia. The ecoregion includes several island groups in the southwestern Banda Sea, including the Tanimbar Islands, Kai Islands, and the Barat Daya Islands e ...
ecoregion includes the Barat Daya Islands (except for Wetar), the
Tanimbar Islands The Tanimbar Islands, also called ''Timur Laut'', are a group of about 65 islands in the Maluku province of Indonesia. The largest and most central of the islands is Yamdena; others include Selaru to the southwest of Yamdena, Larat and Ford ...
, and the
Kai Islands The Kai Islands (also Kei Islands) of Indonesia are a group of islands in the southeastern part of the Maluku Islands, located in the province of Maluku. The Moluccas have been known as the Spice Islands due to regionally specific plants such ...
.


Threats and preservation

More than half of the original vegetation of the islands has been cleared for planting of rice and other crops, for settlement and by consequent forest fires. Only Sumbawa now contains a large area of intact natural forest, while Komodo, Rincah and Padar are now protected as
Komodo National Park Komodo National Park ( Indonesian: ''Taman Nasional Komodo'') is a national park in Indonesia located within the Lesser Sunda Islands in the border region between the provinces of East Nusa Tenggara and West Nusa Tenggara. The park includes the ...
. While many ecological problems affect both small islands and large landmasses, small islands suffer their particular problems and are highly exposed to external forces. Development pressures on small islands are increasing, although their effects are not always anticipated. Although Indonesia is richly endowed with natural resources, the resources of the small islands of Nusa Tenggara are limited and specialised; furthermore human resources in particular are limited.Monk (1996), page 1 General observationsBeller, W., P. d'Ayala, and P. Hein. 1990. ''Sustainable development and environmental management of small islands.'' Paris and New Jersey: United Nations Educational, Scientific, and Cultural Organisation and Parthenon Publishing Group Inc.; Hess, A, 1990. Overview: sustainable development and environmental management of small islands. In ''Sustainable development and environmental management of small islands.'' eds W. Beller, P. d'Ayala, and P. Hein, Paris and New Jersey: United Nations Educational, Scientific, and Cultural Organisation and Parthenon Publishing Group Inc. (both cited in Monk) about small islands that can be applied to Nusa Tenggara include: * A higher proportion of the landmass will be affected by
volcanic activity Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a ...
, earthquakes, landslips, and cyclone damage; * Climates are more likely to be
maritime Maritime may refer to: Geography * Maritime Alps, a mountain range in the southwestern part of the Alps * Maritime Region, a region in Togo * Maritime Southeast Asia * The Maritimes, the Canadian provinces of Nova Scotia, New Brunswick, and Prin ...
influenced; *
Catchment area In human geography, a catchment area is the area from which a location, such as a city, service or institution, attracts a population that uses its services and economic opportunities. Catchment areas may be defined based on from where people are ...
s are smaller and degree of
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
higher; * A higher proportion of the landmass is made up of coastal areas; * A higher degree of environmental specialisation, including a higher proportion of
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
species in an overall
Depauperate A depauperate ecosystem is an ecosystem which is lacking in numbers or variety of species, often because it lacks enough stored chemical elements and resources required for life. Thus, depauperate ecosystems often cannot support rapid growth of f ...
community; * Societies may retain a strong sense of culture having developed in relative isolation; * Small island populations are more likely to be affected by economic migration. File:Palau Banta Nusa Tenggara Barat Indonesia.jpg, Banta Island of Lesser Sunda Islands File:Rinca Island.jpg,
Rinca Rinca, also known as Rincah, Rindja, Rintja and Pintja, is a small island near Komodo and Flores island, East Nusa Tenggara, Indonesia, within the West Manggarai Regency. It is one of the three largest islands included in Komodo National Park. Th ...
island File:Komodo dragon at Komodo National Park.jpg,
Komodo dragon The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant ...
at Komodo National Park


Administration

The Lesser Sundas comprise many islands, most of which are part of
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
and are administered as the
provinces A province is almost always an administrative division within a country or state. The term derives from the ancient Roman '' provincia'', which was the major territorial and administrative unit of the Roman Empire's territorial possessions ou ...
of Bali,
West Nusa Tenggara West Nusa Tenggara ( id, Nusa Tenggara Barat – NTB) is a province of Indonesia. It comprises the western portion of the Lesser Sunda Islands, with the exception of Bali which is its own province. Mataram, on Lombok, is the capital and largest ...
,
East Nusa Tenggara East Nusa Tenggara ( id, Nusa Tenggara Timur – NTT; pt, Sonda Oriental) is the southernmost province of Indonesia. It comprises the eastern portion of the Lesser Sunda Islands, facing the Indian Ocean in the south and the Flores Sea in the nor ...
and the southern part of Maluku. The eastern half of
Timor Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, also ...
is the separate nation of
East Timor East Timor (), also known as Timor-Leste (), officially the Democratic Republic of Timor-Leste, is an island country in Southeast Asia. It comprises the eastern half of the island of Timor, the exclave of Oecusse on the island's north-west ...
.


Demographics


Religion


See also

* Apostolic Vicariate of Lesser Sunda Islands (originally an Apostolic Prefecture) *
Banda Arc The Banda Arc (main arc, Inner, and Outer) is a set of island arcs in eastern Indonesia. It is the result of the collision of a continent and an intra-oceanic island arc. The presently active arc is located on what appears to be oceanic crust whe ...
*
Greater Sunda Islands The Greater Sunda Islands ( Indonesian and Malay: ''Kepulauan Sunda Besar'') are four tropical islands situated within Indonesian Archipelago, in the Pacific Ocean. The islands, Borneo, Java, Sulawesi and Sumatra, are internationally recognised ...
*
Islands of Indonesia The islands of Indonesia, also known as the Indonesian Archipelago ( id, Kepulauan Indonesia) or Nusantara, may refer either to the islands comprising the country of Indonesia or to the geographical groups which include its islands. Histor ...
*
List of rivers of Lesser Sunda Islands A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organizations * List College, an undergraduate division of the Jewish Theological Seminary of America * SC Germania List, German rugby unio ...
*
Oceanic trench Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...
*
Plate tectonic Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
* Sunda Arc * Sundaland *
Sunda Shelf Geologically, the Sunda Shelf is a south-eastern extension of the continental shelf of Mainland Southeast Asia. Major landmasses on the shelf include the Bali, Borneo, Java, Madura, and Sumatra, as well as their surrounding smaller islands. I ...
*
Sunda Trench The Sunda Trench, earlier known as and sometimes still indicated as the Java Trench, is an oceanic trench located in the Indian Ocean near Sumatra, formed where the Australian- Capricorn plates subduct under a part of the Eurasian Plate. It is ...


Notes


References

*


External links

*
LexiRumah
(part of th
Lesser Sunda linguistic databases

Reconstructing the past through languages of the present: the Lesser Sunda Islands
{{Use dmy dates, date=April 2018 Archipelagoes of Indonesia Archipelagoes of Southeast Asia International archipelagoes Maritime Southeast Asia Tropical and subtropical dry broadleaf forests Volcanic arc islands Wallacea