Sumba is an island of Lesser Sunda, located at between Sumbawa and Timor. The island which is composed primarily of sandstone and mudstone, with some igneous intrusions overlain by recent limestone (Whitten and Whitten 1992). Sumba is believed to be a fragment of the Australian continental crust that was separated some 20 million years ago, well before the neighboring outer arc island of Timor (Monk et al. 1997). The island is quite rugged, consisting of deeply dissected plateaus. There is very little area above 1,000 m, and the highest point on the island is 1,225 m (Stattersfield et al. 1998). Precipitation in Sumba is seasonal, and based on the Köppen climate zone system, this ecoregion falls in the tropical dry climate zone (National Geographic Society 1999).
The naturally dominant vegetation of the island was deciduous monsoon forest (Stattersfield et al. 1998). However, the southern hill slopes along the southern coasts, which remain moist during the dry season, are covered with lowland evergreen rain forest. The most extensive and important of these rain forest areas is the Mt. Wanggameti-Laiwanga forest complex in East Sumba, a major water catchment. In East Sumba there are extensive gallery forests in ravines and along rivers that form riparian corridors across open grasslands or savannas. The savanna understory includes an endemic insectivorous sundew (Drosera indica) (Monk et al. 1997).
The avifauna of this ecoregion is highly distinctive, with both Asian and Australian influences, although the total diversity is low. There are approximately 180 bird species on the island, and 12 of these species are endemic or near endemic (table 1). The ecoregion corresponds to the Sumba EBA. The Sumba EBA contains twelve restricted-range bird species, seven of which are found nowhere else on Earth. Four of these species are considered vulnerable: Sumba buttonquail (Turnix everetti), red-naped fruit-dove (Ptilinopus dohertyi), Sumba boobook (Ninox rudolfi), and Sumba hornbill (Aceros everetti). These threatened species have specific habitat needs that make them susceptible to forest clearance (Stattersfield et al. 1998).
Here are the endeemic birds of Sumba:
- Sumba buttonquail (Turnix everetti)
- Sumba green-pigeon (Treron teysmannii)
- Red-naped fruit-dove (Ptilinopus dohertyi)
- Sumba boobook (Ninox rudolfi)
- Cinnamon-backed kingfisher (Todirhamphus australasia)
- Sumba hornbill (Aceros everetti)
- Sumba cuckoo-shrike (Coracina dohertyi)
- Chestnut-backed thrush (Zoothera dohertyi)
- Flores jungle-flycatcher (Rhinomyias oscillans)
- Sumba flycatcher (Ficedula harterti)
- Yellow-spectacled white-eye (Zosterops wallacei)
- Apricot-breasted sunbird (Nectarinia buettikoferi)
Pressures from the rapidly increasing, poor population are intense in this ecoregion (WWF-Indonesia n.d.), and nearly three-quarters of this ecoregion has been deforested, with only isolated fragments of natural habitat remaining.
Types and Severity of Threats
Threats include deforestation, burning of grasslands to establish agricultural fields, livestock grazing, and poaching (WWF-Indonesia n.d.). Much of the forest has already been replaced by fire-resistant casuarinas or eucalypts and extensive deciduous scrub. For instance, the ecoregion’s dry thorny forest, which is especially vulnerable to clearance by fire, has almost completely disappeared (Monk et al. 1997).
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 (1997): Lesser Sundas Deciduous Forests [AA0201], 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 [AA0204], corresponding to the Timor biogeographic unit; and the Sumba Deciduous Forests [AA0203], corresponding to the Sumba biogeographic unit. All three ecoregions belong to the tropical dry forests biome.