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.
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.
|Table 1. Endemic and Near-Endemic Mammal Species.|
|An asterisk signifies that the species' range is limited to this ecoregion.|
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.
|Table 2. Endemic and Near-Endemic Bird Species.|
|Columbidae||Dusky cuckoo-dove||Macropygia magna|
|Columbidae||Flores green-pigeon||Treron floris*|
|Columbidae||Pink-headed imperial-pigeon||Ducula rosacea|
|Columbidae||Dark-backed imperial-pigeon||Ducula lacernulata|
|Psittacidae||Wallace's hanging-parrot||Loriculus flosculus*|
|Loriidae||Olive-headed lorikeet||Trichoglossus euteles|
|Strigidae||Flores scops-owl||Otus alfredi*|
|Strigidae||Wallace's scops-owl||Otus silvicola*|
|Alcedinidae||Cinnamon-backed kingfisher||Todirhamphus australasia|
|Alcedinidae||White-rumped kingfisher||Caridonax fulgidus*|
|Meliphagidae||Sunda honeyeater||Lichmera lombokia*|
|Pachycephalida||Bare-throated whistler||Pachycephala nudigula*|
|Rhipiduridae||Brown-capped fantail||Rhipidura diluta*|
|Monarchidae||Flores monarch||Monarcha sacerdotum*|
|Corvidae||Flores crow||Corvus florensis*|
|Campephagidae||Sumba cuckoo-shrike||Coracina dohertyi|
|Campephagidae||Flores minivet||Pericrocotus lansbergei*|
|Turdidae||Chestnut-backed thrush||Zoothera dohertyi|
|Muscicapidae||Flores jungle-flycatcher||Rhinomyias oscillans|
|Zosteropidae||Yellow-spectacled white-eye||Zosterops wallacei|
|Zosteropidae||White-browed white-eye||Lophozosterops superciliaris*|
|Zosteropidae||Dark-crowned white-eye||Lophozosterops dohertyi*|
|Zosteropidae||Flores white-eye||Heleia crassirostris*|
|Sylviidae||Russet-capped tesia||Tesia everetti*|
|Sylviidae||Timor leaf-warbler||Phylloscopus presbytes|
|Dicaeidae||Golden-rumped flowerpecker||Dicaeum annae*|
|Dicaeidae||Black-fronted flowerpecker||Dicaeum igniferum*|
|Dicaeidae||Red-chested flowerpecker||Dicaeum maugei|
|Nectariniidae||Flame-breasted sunbird||Nectarinia solaris|
|An asterisk signifies that the species' range is limited to this ecoregion.|
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.
During World War II, logging and cultivation destroyed much of the forest cover of Lombok, east Flores, and the small islands of Adonara, Solor, Lomblen, Pantar, and Alor. The Lombok dipterocarp forest is almost depleted by commercial logging, and the forest of Sumbawa is partially covered by a mining concession.
More than half of this ecoregion's natural habitat has been cleared, mainly for agriculture. Except for the island of Sumbawa, which still contains a large block of intact forest, most of the islands in this group have only fragments of natural habitat remaining. The twenty-eight protected areas include about 10 percent of the ecoregion area, but most of the protected areas are small, with the average size being only 144 square kilometers (km2) (Table 3). Komodo National Park, the most famous wild area in the Lesser Sundas, a World Heritage Site, and an important tourist destination, is only one of two reserves that is greater than 500 km2, but most of this park is marine. The park harbors the Komodo dragon. Lowlands are underrepresented in the protected areas system even though this habitat supports most of the ecoregion's species; for instance, most of Sumbawa's endemic birds are associated with lowland monsoon forest.
|Table 3. WCMC Protected Areas That Overlap with the Ecoregion.|
|Protected Area||Area (km2)||IUCN Category|
|Tambora Utara GR||480||PRO|
|Gunung Rinjani||830 + 760 ext.||II|
|Hutan Dompu Complex||110||PRO|
|Gunung Olet Sangenges NR||280-350||PRO|
|Batu Gendang Forest||150||PRO|
|Selahu Legini Complex||320-500||VI|
|Tanjung Kerita Mese||300||PRO|
|Danau Rana Mese||2||PRO|
|Gunung Ambu Lombo||40||PRO|
|Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.|
Increasing population pressure has also resulted in high rates of deforestation. In the dry season, fires often are set to clear the understory and to encourage new growth as forage for domestic animals. This has been done since prehistoric times-not for domestic animals, but for attracting game (introduced) into areas of new grass growth. This practice has resulted in the proliferation of fire-resistant trees such as Casuarina junghuhniana and formation of grassland over an extensive area of these islands. Most of the remaining forest is confined to the steepest slopes and the tops of mountains. Poorly managed tourism, especially in the Komodo National Park and on Lombok, has also caused environmental degradation.
Types and Severity of Threats
Justification of Ecoregion Delineation
The drier forests in Nusa Tenggara were placed in three ecoregions that corresponded to the biogeographic units identified in Monk et al. These are Lesser Sundas deciduous forests, which includes the chain of islands extending from Lombok, Sumbawa, Komodo, Flores, and the smaller satellite islands corresponding to the Flores biogeographic unit; Timor and Wetar deciduous forests, corresponding to the Timor biogeographic unit; and the Sumba deciduous forests, corresponding to the Sumba biogeographic unit. All three ecoregions belong to the tropical dry forests biome.
Additional Information on this Ecoregion
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
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