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Asia: Bhutan, India, and Nepal

This ecoregion contains the highest densities of tigers, rhinos, and ungulates in Asia. One of the features that elevates it to the Global 200 is the diversity of ungulate species and extremely high levels of ungulate biomass recorded in riverine grasslands and grassland-forest mosaics (Seidensticker 1976; Dinerstein 1980). The world's tallest grasslands, found in this ecoregion, are the analogue of the world's tallest forests and are a phenomenon unto themselves. Very tall grasslands are rare worldwide in comparison with short grasslands and are the most threatened. Tall grasslands are indicators of mesic or wet conditions and nutrient-rich soils. Most have been converted to agricultural use.

  • Scientific Code
    (IM0701)
  • Ecoregion Category
    Indo-Malayan
  • Size
    13,400 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Location and General Description
The Terai-Duar Savanna and Grasslands [IM0701] ecoregion sits at the base of the Himalayas, the world's youngest and tallest mountain range. About 25 km wide, this narrow lowland ecoregion is a continuation of the Gangetic Plain. The ecoregion stretches from southern Nepal's Terai, Bhabar, and Dun Valleys eastward to Banke and covers the Dang and Deokhuri Valleys along the Rapti River. A small portion reaches into Bhutan, and each end crosses the border into India's states of Uttar Pradesh and Bihar.

This ecoregion covers a wide range of habitat types-savanna grasslands, evergreen and deciduous forests, thorn forest, and steppe-corresponding to different moisture conditions (Shrestha and Joshi 1997). Low in elevation, this ecoregion is hot and humid in the summer, and during the late dry season temperatures commonly reach 40(C (FAO 1981). Annual monsoon floods deposit silt from the rivers that meander across the grasslands (Mishra and Jeffries 1991). Areas buried in silt return to tall grasslands by the end of the following monsoon, and low-lying areas inundated for a few days only are recharged with an annual load of nutrients (Dinerstein 2002).

In the Nepal Terai, which include the tallest grasslands in the world, characteristic species include Saccharum spontaneum, Saccharum benghalesis, Phragmitis kharka, Arundo donax, Narenga porphyracoma, Themeda villosa, Themeda arundinacea, and Erianthus ravennae and shorter species such as Imperata cylindrica, Andropogon spp., and Aristida ascensionis (Shrestha and Joshi 1997). The grasses are fire and flood resistant and spread rapidly under favorable conditions.

Saccharum spontaneum (kans) grasslands are dominated by this tallgrass species, which is the first to colonize the exposed silt plains after the retreat of monsoon floods. This often occurs in almost pure stands, forming a thin strip on the first terrace of the floodplain. This is the keystone habitat for rhinoceroses and other large mammals. Saccharum benghalesis (baruwa) grasslands dominate the next terrace above the S. spontaneum band along the river's edge. Grazing lawns (chaurs) are very short mixes of grasses maintained by intense grazing by greater one-horned rhinoceroses and other large ungulates. Imperata cylindrica, Chrysopogon aciculatus (kuro), Eragrostis spp., and many short grasses typically dominate them. Cymbopogon spp. (ganaune gans) is another short grass species that occurs in distinct associations on the floodplain and is eaten by greater one-horned rhinoceroses and elephants. The tall grasses Arundo donax and Phragmites karka (narkot) surround oxbows and lakes (Dinerstein 2002).

The alluvial terrain blends into the forested hills, where sal (Shorea robusta) forests are common. These forests average between 25 and 40 m in height but may reach 45 m under favorable conditions (FAO 1981). Moist sal forest is found in eastern and central Nepal, whereas western Nepal's sal forests are drier (Shrestha and Joshi 1997). Common associates include Terminalia tomentosa, Syzygium cuminii, Anogeissus latifolia, Terminalia alata, T. belerica, T. chebula, Lagerstromia parviflora, Dillenia pentagyna, Syzigium operculata, Carya arborea, and Buchanania latifolia, as well as chir pine (Pinus roxburghii) on higher reaches (Dinerstein 2002; FAO 1981).

This ecoregion also contains small patches of tropical deciduous riverine forest dominated by Mallotus philippinensis, Syzigium cuminii, Bombax ceiba, Trewia nudiflora, and Garuga pinnata (Shrestha and Joshi 1997). Another variant, tropical evergreen forest, is made up of Michelia champaca, Syzigium, Cedrela toona, Garuga pinnata, and Duabanga (Shrestha and Joshi 1997). Around the Koshi-Tappu Wildlife Reserve, Ghodaghodi Tal, Bishajaari Tal, oxbow lakes and wetlands provide an additional habitat type.

Biodiversity Features
This ecoregion contains the highest densities of tigers, rhinos, and ungulates in Asia. Royal Chitwan National Park in southern Nepal contains more than 500 of the world's 1,000 endangered greater one-horned rhinoceroses (Rhinoceros unicornis) and about seventy breeding tigers (Panthera tigris) (King Mahendra Trust for Nature Conservation, pers. comm.). Royal Bardia National Park, Royal Shukla Phanta Wildlife Reserve, and Dudwa National Park contain approximately eighty-five more breeding tigers (WWF and ICIMOD 2001). This ecoregion overlaps with three Level I TCUs and one Level II TCU (Dinerstein et al. 1997). The Chitwan-Parsa-Valmiki is a Level 1 TCU that spans southern Nepal and northern India. These three reserves form an important transboundary area for wildlife conservation in general and for tigers in particular. This TCU was evaluated as the most important among all the alluvial grassland units containing tigers on the Indian subcontinent (Dinerstein et al. 1997; Wikramanayake et al. 1998). The TCU supports a healthy leopard population and at least a small population of the rare clouded leopard, the last new large mammal to be reported for Chitwan, representing a range extension of more than 250 km to the west (Dinerstein and Mehta 1989).

Many of the terai grasslands and floodplain forests support five deer species (swamp deer, sambar, axis deer, hog deer, and barking deer), an unusually diverse assemblage of cervids. Four large herbivores, the Asian elephant, greater one-horned rhinoceros, gaur (seasonal occupant), and nilgai or blue bull (in drier grasslands) also co-exist (Dinerstein 2002). Several endangered mammalian herbivores are also present, including the Asiatic wild buffalo and the near-endemic hispid hare (Caprolagus hispidus) (Bell et al. 1990) (table 1). The pygmy hog is another highly endangered ungulate of the very tall grasslands and a strict endemic to this ecoregion (Oliver 1980) (table 1).

Table 1. Endemic and Near-Endemic Mammal Species.

Family Species
Suidae Sus salvanius*
Leporidae Caprolagus hispidus

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

Riverine grasslands in the Terai also provide critical habitat for now-endangered reptiles, including the rare, primitive crocodilian, the gharial (Maskey 1979), mugger crocodile, and soft-shelled turtles (Zug and Mitchell 1995).

This ecoregion overlaps with small portions of two EBAs. It overlaps with the Central Himalayas EBA (129) in western Nepal and the far western portion of the Assam Plains EBA (131) south of Bhutan (Stattersfield et al. 1998). Three near-endemic bird species are found in the Terai (table 2). The Manipur bush-quail (Perdicula manipurensis) is considered vulnerable (IUCN 2000). The Terai's diverse grasslands, riparian woodlands, hill forests, and scrub forests provide a diverse set of habitats for many bird species. More than 375 bird species are found in this ecoregion.

Table 2. Endemic and Near-Endemic Bird Species.

Family Common Name Species
Phasianidae Manipur bush-quail Perdicula manipurensis
Sylviidae Grey-crowned prinia Prinia cinereocapilla
Timaliidae Spiny babbler Turdoides nipalensis

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

Nepal's list of threatened birds, numbering 130 breeding and wintering species, includes 44 species that are found in grasslands or wetlands and 14 species that are grassland specialists. The grassland-associated birds include the Bengal florican (Houbaropsis bengalensis), lesser florican (Sypheotides indica), sarus crane (Grus antigone), and large grass warbler (Graminicola bengalensis). Most are declining in numbers (Dinerstein 2002).

Current Status
The alluvial grassland fragments of this ecoregion now represent remnants of a once-extensive ecosystem. The extremely productive alluvial grasslands, which provide important habitats to endangered large animals such as tigers and elephants, are also good arable land, and most of the grasslands have been converted to agriculture. Perhaps no more than 2.0 percent of the alluvial grasslands of the Gangetic floodplain remains intact, and the best-conserved examples of floodplain grasslands are in Royal Chitwan National Park, Royal Shukla Phanta Wildlife Reserve, Dudhwa National Park, and to a lesser extent Royal Bardia National Park (table 3) (Dinerstein 2002). An extensive network of reserves has been established in the Terai; the challenge now is to connect these reserves to allow wide-ranging species, such as tigers, elephants, and rhinoceros, to move among reserves.

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

Protected Area Area (km2) IUCN Category
Dudwha 570 II
Katarniaghat 530 IV
Royal Shukla Phanta 320 IV
Royal Bardia National Park [IM0115] 1,840 II
Parsa Wildlife Reserve [IM0115] 90 IV
Royal Chitwan National Park [IM0115] 932 II
Mahananda 60 IV
Buxa 100 IV
Garumara 10 IV
Koshi Tappu Wildlife Reserve 140 IV
Total 4,592  

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

Almost all the forest remnants are found in the dry bhabar region, which consists of gravelly soil that has eroded from the foothills and is unsuitable for agriculture (Inskipp 1989). One of the most important forest remnants is protected by Royal Chitwan National Park in southern Nepal (Mishra and Jeffries 1991).

For a long time, malaria kept the human population density low in the Terai, allowing some of the habitat to be set aside, first as hunting reserves for royalty and later as wildlife sanctuaries. More recently, landmark legislation that allowed park revenues and buffer zone projects to make possible viable ecotourism and community forestry projects has enhanced conservation efforts and promoted regeneration of wildlife habitats (Dinerstein 2002).

In 1993, a major reform in Nepal's national policy allowed legal buffer zones to be created around existing protected areas. Management of these zones was taken on by local User Group Committees (UGCs), providing that they developed effective management plans based on sustainable resource use. Additional landmark legislation came in 1995, when Nepal's parliament ratified a series of bylaws requiring that 50 percent of the revenue generated by protected areas be allocated to local development programs in these buffer zones instead of returning to the Ministry of Finance. Now operational, these two initiatives paved the way for establishing legal economic incentives to reduce pressures on core reserves and to conserve wildlife habitats outside parks. More importantly, they allowed villagers to become partners in the recovery of the buffer zones and to serve as guardians of endangered wildlife and habitat (Dinerstein 2002).

Types and Severity of Threats
The Terai is Nepal's major area for logging and wood industries (FAO 1981). Sawmilling is the largest wood-based industry, with private sawmills spread over most of the Terai districts. Fuelwood production is also important, with most consumed within the country and the rest exported to India (FAO 1981). Main species harvested from these forests are Shorea robusta, Terminalia tomentosa, Dalbergia sissoo, Bombax ceiba, and Adina cordifolia (FAO 1981). In addition to the recorded log production, some unauthorized cutting for export is known to have occurred (FAO 1981).

Growing population pressure in the hills has led to migration to and settlement in the Terai, both spontaneously and through government-sponsored resettlement programs (FAO 1981). The southern parts of the Terai therefore are densely populated, and most of the area is under cultivation, although northern regions have a lower population density (FAO 1981). Water diversion, especially for irrigation projects, poses another significant threat. Poaching and overgrazing are also problems here. Much of the savanna grasslands may be created by burning by pastoralists and other human intervention (Shrestha and Joshi 1997).

Justification of Ecoregion Delineation
MacKinnon (1997) follows Rodgers and Panwar (1988) in his classification of the Himalayan biounits and identified two biounits: the Trans-Himalayan (I1) and the Himalayas (I2). The Himalayan Range is divided into four subunits along the longitudinal axis: the Northwest Himalayas (I2a), West Nepal (I2b), Central Himalayas (I2c), and Eastern Himalayas (I2d). We distinguished the altitudinal bands of habitat as distinct ecoregions while retaining several of MacKinnon's subunits that are based on east-west-oriented biogeographic barriers. The Terai-Duar savannas and grasslands are one of these habitats, and they are located along the foothills and to the north of the Siwalik Hills. All the Himalayan ecoregions are part of Udvardy's Himalayan highlands biogeographic province.

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

Prepared by: Eric Dinerstein and Colby Loucks
Reviewed by:

 

The Global 200

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