Andaman Islands rainforests
Andaman Islands (Source: Venkatesh K from Bangalore, India, via Wikimedia Commons)
Located between the Bay of Bengal (Bay of Bengal) and the Andaman Sea, between India to the west and Myanmar to the east, the Andaman Islands are affiliated with both countries in important ways. Although politically part of India, the archipelago is biogeographically more similar to Myanmar and other areas of Indochina. Its rainforests are relatively intact, although the human population is growing fast, posing a serious threat to this isolated ecoregion.
Location and general description
WWF
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 kilometers (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 degrees Celsius and 3000 to 3800 millimeters 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 and many underwater seamounts. 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 million years 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. The highest point in the Andamans is Saddle Peak, at 720 meters (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.
| 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* *Signifies that the species' range is limited to this ecoregion (Andaman Islands rainforests) |
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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. 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 the Keruing Belimbing Tree (Dipterocarpus grandiflorus), 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 SouthAndaman. 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.
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.
| 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 *Signifies that the species' range is limited to this ecoregion (Andaman Islands rainforests) |
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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.
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.
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. 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.
Current status
Table 3. Protected Areas that Overlap with the Ecoregion. Protected Area Area (km2) Little Andaman Island 300 Narcondum Island 7 North Andaman Island 180 South Andaman Island 110 Total 597 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. The Narcondum Island protected area was created for the island's endemic hornbill, Aceros narcondami. (Andaman Islands rainforests) ==Types of 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. 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). 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 to prevent environmental damage. ==Justification of ecoregion delineation==  Andamen Islands, India. (Photograph by Arjun Rajagopalan) Following MacKinnon, we placed the Andaman Islands in a distinct ecoregion, the Andaman Islands Rain Forests. However, we included the Nicobar Islands Rain Forests in this bioregion based on recommendations by Tim Whitmore. Udvardy placed both island chains into the Andaman and Nicobar Islands biogeographic province. |
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