Southern Asia: Between the Bay of Bengal and the Andaman Sea

The Andaman Islands were connected to mainland Myanmar during the Pleistocene. However, the islands still contain a lot of endemic animals and species shared only with the Nicobar Islands. Interestingly, the Andamans are floristically more like the mainland than the Nicobars, with less overlap of plant species than one might expect. Much of the islands are part of protected areas, but the protected areas often are not in the best location for conserving terrestrial species. There are also increasing threats to the biodiversity of the islands from a growing immigration of mainland people.

  • Scientific Code
  • Ecoregion Category
  • Size
    2,200 square miles
  • Status
  • Habitats

 Location and General Description
The Andamans are made up of 204 islands of varying size and are located in the eastern Indian Ocean as part of the Bay of Bengal. Politically almost all the islands belong to India, although a few small islands in the northernmost end of the archipelago belong to Myanmar (e.g., Table, Great Coco, and Little Coco islands).

North Andaman lies 285 km south of Myanmar (a few smaller islands are closer), and the 150-km-wide Ten Degree Channel separates the Andamans from the Nicobars. The Andamans are warm tropical, with temperatures ranging from 22 to 30(C and 3,000-3,800 mm annual average rainfall. Rainfall is heavily influenced by monsoons, which come from the southwest (May to September) and from the northeast (October to December).

The Andamans are geologically part of long island arch that runs from Arakan Yoma in Myanmar to the Mentawai Islands off Sumatra and include the Nicobar Islands Rain Forests [IM0133] and many underwater sea mounts. The arch was formed as the uplift along the subduction of the Indian-Australian plate in the late Eocene or early Oligocene. The opening of the Andaman Sea in the middle Miocene (about 10.8 m.y. ago) marked the first isolation of the Andamans from the mainland. Falling sea levels of the Pleistocene reconnected the islands to the mainland Myanmar for a period about 10,000 years ago (Das 1999). The highest point in the Andamans is Saddle Peak, at 720 m. The higher elevations of the Andamans often contain serpentine and gabbro formations, and at lower elevations Eocene sediments (sandstones, shales, and siltstones) with ultrabasic igneous intrusions predominate (Rao 1996).

The main categories of natural vegetation of the Andamans are coastal and mangrove forests and the interior evergreen and deciduous forests. Mangroves are extensive in the Andamans and make up about 15 percent of the total land area. All the most common trees belong to the family Rhizophoraceae and tend to reach heights of 6-24 m (Balakrishnan 1989). Evergreen forests form on clayey loam soils with poor humus content on top of micaceous sandstones. Dominant tree species reach heights of 40-60 m, including Dipterocarpus griffithii, D. turbinatus, Sideroxylon longipetiolatum, Hopea odorata, Endospermum malaccense, and Planchonia andamanica. Deciduous forests exist mainly on North Andaman, Middle Andaman, and Baratang Island and parts of South Andaman. They shed their leaves (either fully or partially) during the dry season and often are composed of tall trees reaching 40-50 m, including Terminalia procera, T. bialata, T. manii, Canarium euphyllum, Ailanthes kurzii, Parishia insignis, Diploknema butyracea, Albizia lebbek, Tetrameles nudiflora, and Pterocymbium tinctorium (Balakrishnan 1989; Rao 1996).

Biodiversity Features
The Andaman Islands have five mammal species that are strictly endemic to the ecoregion (table 1). All five species are listed as threatened (categories vulnerable and above) (IUCN 2000).

Table 1. Endemic and Near-Endemic Mammal Species.

  Family Species
Sorcidae Crocidura hispida*
Sorcidae Crocidura andamanensis*
Sorcidae Crocidura jenkinsi*
Rhinolophidae Rhinolophus cognatus*
Muridae Rattus stoicus*

An asterisk signifies that the species' range is limited to this ecoregion.

There are eight strictly endemic bird species and four near endemics in the Andamans (table 2). Additionally, one species not listed in table 2 is Nicobar scrubfowl (Megapodius nicobariensis), which used to live in both the Andamans and Nicobars but is now found only in the latter. One of the strict endemics, Aceros narcondami, is considered threatened (IUCN categories VU and above) and is found only on the small volcanic island of Narcondam.

Table 2. Endemic and Near-Endemic Bird Species.

  Family Common Name Species
Accipitridae Andaman serpent-eagle Spilornis elgini*
Rallidae Andaman crake Rallina canningi*
Columbidae Andaman wood-pigeon Columba palumboides
Columbidae Andaman cuckoo-dove Macropygia rufipennis
Cuculidae Andaman coucal Centropus andamanensis*
Strigidae Andaman scops-owl Otus balli*
Strigidae Andaman hawk-owl Ninox affinis
Bucconidae Narcondam hornbill Aceros narcondami*
Picidae Andaman woodpecker Dryocopus hodgei*
Dicruridae Andaman drongo Dicrurus andamanensis*
Corvidae Andaman treepie Dendrocitta bayleyi*
Sturnidae White-headed starling Sturnus erythropygius

An asterisk signifies that the species' range is limited to this ecoregion.

The Andaman Islands have forty-five reptile species, thirteen of which are endemic. Twelve amphibian species (all frogs and toads) are in the Andamans, seven of which are endemic (Das 1999).

Floristically, the Andamans have much more in common with northeast India, Myanmar, and Thailand than with the Nicobars, which have affinities with Malaysia and Indonesia. In fact, the Andamans and Nicobars share only 28 percent of angiosperm species (Rao 1996). The plants that are not shared between the two island groups are just as revealing. The genera Dipterocarpus and Pterocarpus are both common in the Andamans but are absent from the Nicobars. Otanthera, Astronia, Cyrtandra, Stemonurus, Bentinckia, Rhopaloblaste, and Spathoglottis all occur in the Nicobars but not in the Andamans (Balakrishnan 1989; Rao 1996).

Current Status
The Andaman Islands remain largely forested, and several protected areas exist (table 3). However, the protected areas cover mainly marine habitats and not terrestrial ones (Das 1999). The Narcondum Island protected area was created for the island's endemic hornbill, Aceros narcondami.

Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.

  Protected Area Area (km2) IUCN Category
Little Andaman Island 300 ?
Narcondum Island 7 ?
North Andaman Island 180 ?
South Andaman Island 110 ?
Total 597  

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

Types and Severity of Threats
The main threats to the Andamans are the result of an influx of people from the mainland. Population growth has put greater demands on the natural resources of the islands. Logging rates are high, as are agricultural encroachment (Das 1999). Indigenous people of the Andamans are permitted to exploit wildlife within the parks (unlike in mainland India), but increasing wildlife exploitation is caused mostly by recent immigrants and foreigners.

Introduced species are a problem in the Andamans. Typical island introductions such as rats, dogs, and cats may be harming the endemic Andaman crake (Rallina canningi) (Stattersfield et al. 1998). Spotted deer (Axis axis) are now widespread throughout the Andamans, as is the African giant snail (Achatina fulica). Elephants (Elephas maximus) have been introduced to Interview Island and North Andaman.

The islands have increasingly become a tourist destination, but the industry is not properly regulated (Sinha 1992).

Justification of Ecoregion Delineation
Following MacKinnon (1997), we placed the Andaman Islands in a distinct ecoregion, the Andaman Islands Rain Forests [IM0101]. However, we included the Nicobar Islands Rain Forests [IM0133] in this bioregion based on recommendations by Tim Whitmore (pers. comm., 1999). Udvardy (1975) placed both island chains into the Andaman and Nicobar Islands biogeographic province.

References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List

Prepared by: John Lamoreux
Reviewed by: