The Terai–Duar savanna and grasslands is a narrow lowland ecoregion at the base of the Himalayas, about wide, and a continuation of the Indo-Gangetic Plain in India, Nepal and Bhutan. It is colloquially called Terai in the Ganges Basin east to Nepal, then Dooars in West Bengal, Bhutan and Assam east to the Brahmaputra River. It harbours the world's tallest grasslands, which are the most threatened and rare worldwide. Location and description This tropical and subtropical grasslands, savannas, and shrublands biome stretches from western Bhutan to southern Nepal's Terai, westward to Banke, covering the Dang and Deukhuri Valleys along the Rapti River to India's Bhabar and Doon Valley. Each end crosses the border into India's states of Uttarakhand, Uttar Pradesh and Bihar. The eastern and central areas are wetter than the western end. In Nepal, the wetlands of Koshi Tappu Wildlife Reserve, Beeshazar Tal in the bufferzone of Chitwan National Park, Jagdishpur Reservoir and Ghodaghodi Tal are designated Ramsar sites. The Sukla Phanta Wildlife Reserve is Nepal's largest patch of continuous grassland. Flora The Terai–Duar savanna and grasslands are a mosaic of tall riverside grasslands, savannas and evergreen and deciduous forests, depending on soil quality and the amount of rain each area receives. The grasslands of the Terai in Nepal are among the tallest in the world, and are maintained by silt deposited by the yearly monsoon floods. Important grasses include baruwa (Tripidium bengalense) and kans grass (Saccharum spontaneum), which quickly establishes itself after the retreat of the monsoon waters. In the hillier areas the dominant tree is sal (Shorea robusta), which can grow to a height of . The belt also contains riverside tropical deciduous forest comprising Mallotus philippensis, jamun, cotton tree, Mallotus nudiflorus, and Garuga pinnata. Fauna The ecoregion is habitat for a huge number of mammalian and bird species. Notable are the large numbers of the endangered greater one-horned rhinoceros and Bengal tigers as well as Asian elephants, sloth bears, Indian leopards. In Nepal's Chitwan National Park, more than 400 rhinos were sighted in 2008, and 125 adult tigers were recorded during a survey conducted from December 2009 to March 2010, which covered an area of . Nepal's Bardia National Park and Sukla Phanta Wildlife Reserve, and India's Valmiki and Dudhwa National Parks are home to nearly 100 tigers. Chitwan along with the adjoining Parsa National Park is of major importance, especially for tigers and clouded leopard.