Terai-Duar savanna and grasslands
TheTerai-Duar savanna and grasslands 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.
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 some of the most threatened ecoregion units. Tall grasslands are indicators of mesic or wet conditions and nutrient-rich soils; most have been converted to agricultural use.
Location and general description
The Terai-Duar savanna and grasslands ecoregion sits at the base of the Himalaya Mountains, the world's youngest and yet tallest great mountain range. About 25 kilometers 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. Low in elevation, this ecoregion is hot and humid in the summer, and during the late dry season temperatures commonly reach 40oC. Annual monsoon floods deposit silt from the rivers that meander across the grasslands. Areas buried in silt return to tall grasslands by the end of the following monsoon, and low-lying topography inundated for a few days only are recharged with an annual load of nutrients.
In the Nepal Terai, which include the tallest grasslands on Earth, 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. 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.
The alluvial terrain blends into the forested hills, where sal (Shorea robusta) forests are common. These forests average between 25 and 40 metres in height but may reach 45 metres under favorable conditions. Moist sal forest is found in eastern and central Nepal, whereas western Nepal's sal forests are drier. 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.
This ecoregion also contains small patches of tropical deciduous riverine forest dominated by Mallotus philippinensis, Syzigium cuminii, Bombax ceiba, Trewia nudiflora, and Garuga pinnata. Another variant, tropical evergreen forest, is made up of Michelia champaca, Syzigium, Cedrela toona, Garuga pinnata, and Duabanga. Around the Koshi-Tappu Wildlife Reserve, Ghodaghodi Tal, Bishajaari Tal, oxbow lakes and wetlands provide an additional habitat type.
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). Royal Bardia National Park, Royal Shukla Phanta Wildlife Reserve, and Dudwa National Park contain approximately eighty-five more breeding tigers. This ecoregion overlaps with three Level I TCUs and one Level II TCU. 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. 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 kilometers to the west.
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. Several endangered mammalian herbivores are also present, including the Asiatic wild buffalo and the near-endemic hispid hare (Caprolagus hispidus) (Table 1). The pygmy hog is another highly endangered ungulate of the very tall grasslands and a strict endemic to this ecoregion (Table 1).
|Table 1. Endemic and Near-Endemic Mammal Species.|
|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, mugger crocodile, and soft-shelled turtles.
This ecoregion overlaps with small portions of two Endemic Bird Areas. 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. Three near-endemic bird species are found in the Terai (Table 2). The Manipur bush-quail (Perdicula manipurensis) is considered vulnerable. 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.|
|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.
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 two 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). 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|
|Royal Shukla Phanta||320||IV|
|Royal Bardia National Park||1,840||II|
|Parsa Wildlife Reserve||90||IV|
|Royal Chitwan National Park||932||II|
|Koshi Tappu Wildlife Reserve||140||IV|
|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. One of the most important forest remnants is protected by Royal Chitwan National Park in southern Nepal.
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.
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.
Types and severity of threats
The Terai is Nepal's major area for logging and wood industries. 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. Main species harvested from these forests are Shorea robusta, Terminalia tomentosa, Dalbergia sissoo, Bombax ceiba, and Adina cordifolia. In addition to the recorded log production, some unauthorized cutting for export is known to have occurred.
Growing population pressure in the hills has led to migration to and settlement in the Terai, both spontaneously and through government-sponsored resettlement programs. 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. 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.
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.
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