Lesser Sunda Islands

The Lesser Sunda Islands, officially called Nusa Tenggara in Indonesia, form an archipelago spanning Indonesia and Timor-Leste. Along with the Greater Sunda Islands to their west, they comprise the Sunda Islands. Most of these islands lie within the Wallacea region, but the province of Bali sits west of the Wallace Line on the Sunda Shelf. Geologically, they belong to the Sunda Arc, a volcanic chain created by subduction along the Sunda Trench in the Java Sea. The population grew from 3,460,059 in 1930 to over 17 million today. The name Nusa Tenggara comes from the Indonesian words *nusa* (island) and *tenggara* (southeast), meaning "Southeast Islands."

From west to east, the main islands are Bali, the Kangean Islands, Lombok, Sumbawa, Flores, Sumba, Savu, Rote, Timor, Atauro, the Alor archipelago, the Barat Daya Islands, and the Tanimbar Islands. All are part of Indonesia except the eastern half of Timor and Atauro, which make up the nation of Timor-Leste.

**Geology**

The Lesser Sunda Islands split into two geologically distinct groups. The northern chain—Bali, Lombok, Sumbawa, Flores, and Wetar—is volcanic, formed about 15 million years ago during the Pliocene when the Australian and Asian plates collided. Some volcanoes, like Mount Rinjani on Lombok, remain active; others, such as Ilikedeka on Flores, are extinct. The southern chain—Sumba, Timor, and Babar—is non-volcanic and appears to belong to the Australian plate. The northern archipelago shares its geological history and processes with the southern Maluku Islands, which continue the same island arc eastward. Geological study of the region has a long history dating back to Indonesian colonial times, but the formation and progression are not fully understood, and theories shifted significantly in the late 20th century. Because they sit at the collision of two tectonic plates, the Lesser Sunda Islands are among the most geologically complex and active areas on Earth. Bali is the only part of Nusa Tenggara on the Sunda Shelf, west of the Wallace Line and outside Wallacea. Numerous volcanoes dot the islands.

**Ecology**

Unlike the large islands of Java or Sumatra, the Lesser Sunda Islands consist of many small islands, often separated by deep oceanic trenches. This limits the movement of flora and fauna, leading to a high rate of localized species, most famously the Komodo dragon. As Alfred Wallace described in *The Malay Archipelago*, the Wallace Line runs between Bali and Lombok along the deep Lombok Strait, which acted as a water barrier even when lower sea levels connected other landmasses. Islands east of the Lombok Strait belong to Wallacea, blending Asian and Australasian wildlife. Asian species dominate the Lesser Sundas; Weber’s Line, marking the boundary between parts of Wallacea with mainly Asian versus Australasian species, lies east of the group. These islands have the driest climate in Indonesia, supporting mostly tropical dry broadleaf forests, unlike the tropical moist forests found in most of the country.

**Ecoregions**

The Lesser Sunda Islands are divided into six ecoregions:

- **Eastern Java-Bali rain forests** and **Eastern Java-Bali montane rain forests** cover Bali, the only island in the Indomalayan realm and not part of Wallacea. Bali was once attached to the Asian continent (Sundaland) and hosted large Asiatic mammals such as Asian elephants and the extinct Bali tiger. - **Lesser Sundas deciduous forests** include the northern chain from Lombok and Sumbawa east to Flores and Alor. Higher slopes feature tall *Podocarpus* conifers and *Engelhardias* with an understory of lianas, epiphytes, and orchids like *Corybas*, *Corymborkis*, and *Malaxis*. Coastal plains originally held savanna grasses, including *Borassus flabellifer* palm savannas on Komodo, Rincah, and Flores. Though dry forest dominates, patches of rainforest occur, especially in lowlands and along riverbanks on Komodo, and a dry thorny forest exists on Lombok’s southeast coast. Thorn trees were once common on coastal areas but have largely been cleared. Unique species include 17 endemic birds (out of 273 bird species), the endangered Flores shrew (*Suncus mertensi*), the vulnerable Komodo rat (*Komodomys rintjanus*), the Lombok flying fox (*Pteropus lombocensis*), and the Sunda long-eared bat (*Nyctophilus heran*). The Komodo dragon—the world’s largest lizard, reaching three meters and ninety kilograms—lives on Komodo, Rincah, Gili Motang, and the northwestern coast of Flores. - **Sumba deciduous forests** cover Sumba. - **Timor and Wetar deciduous forests** include Timor, Wetar (in Maluku Province), Rote, and Savu. - **Banda Sea Islands moist deciduous forests**, more humid, cover the Barat Daya Islands (except Wetar), the Tanimbar Islands, and the Kai Islands.

**Threats and preservation**

More than half of the original vegetation has been cleared for rice and other crops, settlement, and resulting forest fires. Only Su...