Zoology

Lesser Sundas deciduous forests

Content Cover Image

Palau Banta Island in the Lesser Sundas. Source: Jialiang Gao

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

caption Rinca Island, Indonesia. (Photograph by WWF-Canon/Michel Terrettaz)

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 3726 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 1349 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.

caption WWF 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.

caption Komodo dragons (Varanus komodoensis), Komodo Island, Indonesia. (Photograph by Eric Wikramanayake)

Dry evergreen forest occurs above dry deciduous forest and below the true evergreen montane forest, at 1000 m above sea level on Mt. Batulante in northwest Sumbawa. Below 1200 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 2000 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 1200 to 2100 m, with lianas, epiphytes, and orchids such as Corybas, Corymborkis, and Malaxis very much in evidence. At higher elevations of up to 2700 m, Casuarina junghuhniana forests occur. Toward the summit, from 3300 to 3400 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 1000 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 1000 to 1500 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.

Table 1. Endemic and Near-Endemic Mammal Species.
Family Species
Soricidae Suncus mertensi*
Pteropodidae Pteropus lombocensis*
Vespertilionidae Nyctophilus heran*
Muridae Bunomys naso*
Muridae Komodomys rintjanus*
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.
Family Common Name 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.

Current Status

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
Pulau Sangiang 150 PRO
Pulau Moyo 160-222 VI
Tambora Utara GR 480 PRO
Tambora Selatan 150 VI
Gunung Rinjani 830 + 760 ext. II
Pulau Panjang 200 PRO
Hutan Dompu Complex 110 PRO
Gunung Olet Sangenges NR 280-350 PRO
Suranadi 5 V
Pulau Rakit 20 PRO
Batu Gendang Forest 150 PRO
Pantai Palolowaru 5 PRO
Selahu Legini Complex 320-500 VI
Kurung Baya/Varanus 40 PRO
East Timor 210 PRO
Tanjung Kerita Mese 300 PRO
Danau Rana Mese 2 PRO
Danau Kelimutu 20 DE
Danau Sano 8 PRO
Gunung Ambu Lombo 40 PRO
Tuti 60 V
Tanjung Watupayung 90 PRO
Hadekawa-Labelakang 250 PRO
Gunung Muna 100-150 PRO
Adonara NR 20 PRO
Pulau Rusa 10 PRO
Egon-Iliwuli 30 PRO
Lewotobi 8 VI
Total 4,048+  
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

The future threats will continue to be deforestation, an increasing population and their demands on the environment, intentionally-set fires, and agricultural land development.

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.

References

  • Monk, K.A.; Fretes, Y., Reksodiharjo-Lilley, G. (1996). The Ecology of Nusa Tenggara and Maluku. Hong Kong: Periplus Editions Ltd. ISBN 962-593-076-0.
  • 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, ISBN 0-19-854185-6
  • Veevers, J.J. (1991) "Phanerozoic Australia in the changing configuration of ProtoPangea through Gondwanaland and Pangea to the present dispersed continents" Australian Systematic Botany 4

 

Disclaimer: This article  contains information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth  have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

 

 

 

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Citation

Fund, W. (2014). Lesser Sundas deciduous forests. Retrieved from http://www.eoearth.org/view/article/51cbee557896bb431f697180

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