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LESSER SUNDAS ISLANDS
A group of islands of
the
western Malay Archipelago between the South China Sea
and the Indian Ocean. The Greater Sunda Islands include
Sumatra, Borneo, Java, and Sulawesi; the Lesser Sunda
Islands lie east of Java and extend from Bali to Timor.
Sumatra and Java are separated by the Sunda Strait, a
narrow channel linking the Indian Ocean with the Java
Sea.
Archipelago extending from the Malay Peninsula to the
Moluccas. The islands make up most of the land area of
Indonesia, with only northern and northwestern Borneo
and the eastern portion of Timor not under Indonesian
political control. They include the Greater Sunda
Islands (Sumatra, Java, Borneo, Sulawesi, and adjacent
smaller islands) and the Lesser Sunda Islands (Bali,
Lombok, Sumbawa, Sumba, Flores, Timor, Alor, and
adjacent smaller islands). Most of the islands are part
of a geologically unstable and volcanically active
island arc. Malay cultures and languages predominate in
the area.
Sunda Islands
(sŭn'də) , mainly in Indonesia, between the South China
Sea and the Indian Ocean, comprising the western part of
the Malay Archipelago. It includes two main groups: the
Greater Sunda Islands, to which belong the largest
islands of Borneo, Sumatra, Java, and Sulawesi; and the
Lesser Sundas, which lie E of Java and include Sumbawa,
Flores, Timor, and Sumba (the largest islands). Bali and
Lombok, although smaller, are the most important of the
Lesser Sundas. The Lesser Sundas, which were renamed
Nusa Tenggara [southeastern islands] in 1954, form two
provinces within Indonesia. Malaysia, Brunei, and East
Timor are the other nations wholly or partially in the
Sunda Islands. The Sunda Strait, 20 to 65 mi (32–100 km)
wide, between Java and Sumatra, connects the Java Sea
with the Indian Ocean.
The
Lesser
Sundas deciduous forests are found on a string of
volcanic islands. They stretch across the Java Sea
between Australia and Borneo. It is part of a unique
biogeographic region known as Wallacea, which contains a
very distinctive fauna representing a mix of Asian and
Australasian species. These distinctive seasonal dry
forests harbor unique species, including the Komodo
dragon, the largest lizard in the world, and seventeen
bird species found nowhere else on Earth. A combination
of shifting agriculture and human-caused fires has
significantly reduced the amount of natural forest in
this ecoregion.
Location and General Description
This ecoregion represents the semi-evergreen dry forests
in the Lesser Sunda Islands. It extends east
from
the islands of Lombok and Sumbawa to Flores and Alor in
the Indonesian Archipelago. Rinjani volcano on Lombok is
the highest mountain in the ecoregion, at 3,726 meters
(m). The Lesser Sundas are an inner volcanic island arc,
created by the subduction and partial melting of the
Australian tectonic plate below the Eurasian plate. The
islands represent Tertiary and Quaternary volcanoes that
have coalesced with lava and sediment. There is actually
a geologic discontinuity between Lombok and Sumbawa, on
the Sunda Arc, and the rest of the islands, part of the
Banda Arc. With the exception of Komodo, which is
Mesozoic, most of the islands were built during two
pulses in the Tertiary (Mio-Pliocene) and Quaternary
(recent). This ecoregion is separated from Bali and Java
to the west by Wallace's Line, which marks the end of
the Sunda Shelf. With an average annual rainfall of
1,349 millimeters (mm), this region is the driest but
also the most seasonal in Indonesia. Based on the Köppen
climate system, this ecoregion has a tropical dry
climate zone. This distinctive climate has given rise to
a vegetation that is strikingly different from that of
the rest of the archipelago. Much of the natural habitat
is composed of monsoon forests and savanna woodlands.
The
monsoon forests consist of several forest subtypes,
notably moist deciduous forest, dry deciduous forest,
dry thorn forest, and dry evergreen forest. Moist
deciduous forests also occur as a band of lowland forest
at the base of the hills and as gallery forests along
streams, especially on Komodo Island. Dominant trees
include Tamarindus indica and Sterculia foetida. The dry
deciduous forest at altitudes below 200 m is dominated
by Protium javanicum, Schleichera oleosa, and Schoutenia
ovata, whereas at medium altitudes, from 200 to 800 m,
the dominant tree is Tabernaemontana floribunda. At
these altitudes, lianas and climbers become common,
especially the white-flowered liana Bauhinia. Above
1,000 m, Euphorbiaceae tend to become common and well
represented.
Dry thorn forest is another type of monsoon forest in
this ecoregion, although little is left because it has
been cleared by setting fires. This forest formation
still exists along the southeast coast of Lombok and the
southwest coast of Sumbawa but is being cleared in the
latter region for road building, mine development, and a
transmigration site.
Dry
evergreen
forest occurs above dry deciduous forest and below the
true evergreen montane forest, at 1,000 m above sea
level on Mt. Batulante in northwest Sumbawa. Below 1,200
m on the north slopes, Albizia chinensis is a
characteristic species. Other common species include
Chionanthus, Prunus, and two Cryptocarya species. On
many islands, drier areas in steep-sided valleys contain
gallery forest. On Sumbawa, for instance, gallery forest
is found from sea level to 2,000 m above sea level and
is also present in lower montane forests. By contrast,
the southern hill slopes along the southern coasts are
kept moist during the dry season by the southeast trade
winds, and dipterocarp rain forest occurs on the
southwest hills of both Lombok and Sumbawa. Lombok also
contains one of the few remaining patches of tropical
semi-evergreen rain forest, at volcanic Mt. Rinjani,
which acts as the major water catchment area for the
whole island.
Twenty-meter-high mixed montane forests of Podocarpus
and Engelhardia are found from about 1,200 to 2,100 m,
with lianas, epiphytes, and orchids such as Corybas,
Corymborkis, and Malaxis very much in evidence. At
higher elevations of up to 2,700 m, Casuarina
junghuhniana forests occur. Toward the summit, from
3,300 to 3,400 m, the rocky ridges were once covered
with lichens, mosses, grasses, herbs, and some ferns but
are now being eroded. On Sumbawa, the south slopes of
Mt. Batulante above 1,000 m are covered with a
Cryptocarya-Meliaceae montane forest, although species
composition varies with moisture. This forest is
dominated by two species of Cryptocarya, one in the
drier and usually lower forest (from 1,000 to 1,500 m
above sea level) and the other at higher or moister
sites. Drier, stonier slopes in poorer forest are the
only places where lianas are common. Further east, from
the eastern part of Flores to Alor, the forests are
dominated by Pterocarpus indicus.
There
are
also two types of savanna in this ecoregion: a Borassus
flabellifer savanna that occurs from sea level to 400 m
on Komodo, Rinca, and the north and south coasts of
Flores; and the Ziziphus mauritiana savanna, which
occurs on more sandy clay alluvial, and sometimes
water-logged, soil. The dominant grasses are Eulalia
leschenaultiana, spear grass (Heteropogon contortus,
Themeda frondosa), and Themeda triandra.
Biodiversity Features
This area, part of the Wallacean sub-region, includes a
mix of Asian and Australian fauna, and because of the
long years of isolation from the mainland it harbors
many endemic mammals and birds. Most of the endemic
mammals occur on Komodo and Flores eastward, rather than
Lombok and Sumbawa. One of the important and
better-known endemic species in this ecoregion is the
Komodo dragon (Varanus komodoensis), the largest lizard
in the world.
The mammal fauna in this ecoregion consists of fifty
species, including five ecoregional endemics, including
the critically endangered Flores shrew (Suncus mertensi)
and the vulnerable Komodo rat (Komodomys rintjanus)
(Table 1). With the exception of the New Caledonia dry
forests, with six endemic mammals, the five endemic
mammals in this ecoregion are more than are found in any
other dry forest ecoregion in the Indo-Pacific.
This ecoregion
also
harbors about 273 bird species, of which 29 are endemic
or near endemic (Table 2). The ecoregion is consistent
with the Northern Nusa Tenggara Endemic Bird Area (EBA).
Of the twenty-nine restricted-range species in the EBA,
seventeen are found nowhere else in the world. Three are
endemic and threatened, including the endangered Flores
monarch (Monarcha sacerdotum) and the vulnerable
Wallace's hanging-parrot (Loriculus flosculus) and
Flores crow (Corvus florensis). In addition, the white-rumped
kingfisher (Caridonax fulgidus) is the sole
representative of an endemic monotypic genus.
The Komodo dragon deserves special mention. It is the
largest lizard species in the world. Varanus komodoensis
occupies five islands: Komodo, Padar, Rinca, Gili Motang,
and Flores. These animals range from sea level to
approximately 450 m in elevation, mainly in tropical
deciduous monsoon forest, tropical savanna, and
grassland. They feed on a wide variety of animal food,
including insects, lizards, snakes, birds, deer, wild
boar, monkeys, and bird eggs; they also feed on carrion.
Adults may have a foraging range of 500 hectares (ha).
There are approximately 4,000 protected individuals in
Komodo National Park.
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