Natural History of the Terai — Grasslands, Forests, Rivers and Extraordinary Diversity

Land made by rivers

Rivers coming out of the Himalaya carry enormous loads of gravel, sand and silt. In the Bhabar, the narrow forest belt nearest the hills, the coarse material is dropped ^[1]. Further out, in the Terai, the rivers slow down and spread out, laying down fine alluvial soil that is renewed every year ^[1].

Dudhwa sits within that system. Official descriptions place the national park between the Mohan river on the north and the Suheli on the south, with the India–Nepal border along its north-western edge ^[2].

Historical records show how unstable these rivers are. The 1877 Gazetteer of the Province of Oudh describes the Suheli as an abandoned channel of the Sarju. It also records a river that, by the 1870s, lay eight miles from a fort it had once passed within three miles of ^[4]. The Khairigarh story follows that history. For wildlife, this restlessness matters: every abandoned channel becomes a wetland, every flood resets a grassland.

Sal forest

The tall, straight-trunked sal tree (Shorea robusta) dominates the Terai's drier, better-drained ground ^[1]. Sal forest shades out much of the undergrowth, and in the dry season it sheds its leaves, opening up the forest floor.

These forests give cover to tigers, leopards, sloth bears and deer. They are also connected to the human history of the Terai, as timber estates managed by the forest department long before Dudhwa became a park.

Tall grassland

Where the ground is lower and wetter, grassland takes over. Locally these grasslands are often called phantas. During the monsoon, tall grasses can stand three to six metres high ^[2]. Grasses such as Saccharum spontaneum and Imperata cylindrica make up much of this early-successional "elephant grass" ^[5].

These grasslands are not permanent. Left alone, many would slowly turn into scrub and forest. They are maintained by flooding, by grazing animals and, in managed areas, by controlled cutting and burning in the dry months. Each of these processes cuts back the woody growth and keeps the grassland open. The balance is delicate. Too much burning or cutting removes the cover grassland animals need, while too little lets the grassland close in ^[5].

Wetlands and rivers

Between forest and grassland lie the Terai's wetlands: shallow lakes (tal or jhil), marshes and the slow channels of old rivers. The gazetteer recorded wild rice in all the jhils of Kheri district ^[4]. Today these wetlands support waterbirds, fishing cats, otters and the swamp deer that give one Dudhwa area its fame.

The larger rivers have their own wildlife. At Katarniaghat the Girwa and Kauriala hold gharial, mugger and Gangetic river dolphin. The gharial story covers them.

The rhythm of the seasons

The Terai's year is shaped by water.

• Monsoon. Rivers flood, low grassland is waterlogged, and the grass grows fast and tall.
• Cool, dry months. The water drains back, the grass dries out and is cut or burned in managed areas, and fresh green shoots appear.
• Hot, dry months. Water shrinks to the permanent wetlands and rivers.

Animals move with these changes. Hispid hares, for example, are recorded moving away from dry-season fires into marshy areas and riverbanks, and away from waterlogged grass during peak monsoon floods ^[5].

Specialists of the grassland

The Terai's grasslands hold a group of species found almost nowhere else.

• Swamp deer (barasingha). These deer depend on wet grasslands and swamps. Dudhwa began as a sanctuary created for them: an area of Lakhimpur Kheri was notified in 1958, first called Sonaripur Sanctuary ^[2].
• Hispid hare (Caprolagus hispidus). A dark, coarse-furred hare of dense tall grassland, listed as Endangered on the IUCN Red List (2019 assessment) ^[5]. It is so rarely seen that a camera-trap photograph taken in Dudhwa's floodplain grasslands in January 2020 was published as a notable record ^[6].
• Bengal florican. A bustard of open grassland, Critically Endangered according to the IUCN. In 2017, sightings of displaying males were still being reported in Dudhwa's South Sonaripur range ^[7]. Bombay Natural History Society studies cited in the same report found that floricans in the Pilibhit–Dudhwa area also use farmland across the Sharda river. That exposes them to pesticides and hunting outside the protected area ^[7].
• Greater one-horned rhinoceros. Reintroduced to Dudhwa from Assam and Nepal in 1984–85, as told in the rhino story.

The official description of Dudhwa National Park names the hispid hare and Bengal florican among its most endangered species, noting that both have been wiped out almost everywhere else in India ^[2].

The tiger and its landscape

Tigers use every part of this mosaic: forest for cover, grassland for hunting deer, and water to drink and keep cool. According to the 2022 national tiger estimation, as reported in 2023, the count for Dudhwa Tiger Reserve rose from 82 in 2018 to 135 in 2022. Uttar Pradesh's total rose from 173 to 205 ^[8]. These are dated estimates from a national survey that is repeated every four years.

Beyond the boundaries

No Terai reserve is large enough on its own. Tigers, elephants and other animals move between protected areas along forest corridors, many of which cross farmland, rivers and the international border.

A 2014 Wildlife Institute of India study of the transboundary Terai Arc Landscape, based on camera trapping in 2012–13, documented tigers moving along the Khata corridor between Nepal's Bardia National Park and Katarniaghat Wildlife Sanctuary ^[9]. The same study found tiger densities ranging from 0.16 per 100 square kilometres in Nepal's Banke National Park to 4.9 per 100 square kilometres in Kishanpur Wildlife Sanctuary ^[9]. A WWF-led project running from 2025 to 2028 is working to secure corridors across the 5,998-square-kilometre Khata–Basanta–Dudhwa complex ^[10].

Watching without disturbing

The Terai rewards patient, quiet observation. A few principles follow from how this ecosystem works:

• Keep to existing tracks, especially in grassland, where ground-nesting birds and hares shelter.
• Keep a generous distance from animals, and give way to elephants and rhinos.
• Use silence and stillness rather than chasing a sighting.
• Never feed wildlife or leave food waste.

The most rewarding encounters often come from reading signs, such as alarm calls, pugmarks and flattened grass, rather than from seeing a large animal.

Why it matters

The Terai's grasslands and wetlands are among the most threatened habitats in South Asia. They are easily converted to farmland, and they depend on floods and active management to persist. Dudhwa is one of the few places in India where the full mosaic and its specialist species survive together. That makes it essential for conserving species such as the hispid hare and Bengal florican.

What this story tells us about Dudhwa today

What a visitor sees in Dudhwa is a living, changing landscape: grasslands kept open by flood and management, sal forest, old river channels turned to wetland, and tigers moving between them. The rarest animals here are grassland specialists. Their survival depends on careful management inside the reserve and on what happens in the fields and corridors beyond it.

In closing

The Terai is a landscape built by water and kept alive by change. Understanding the forces that shape it, from the floods and rivers to grazing, fire and corridors, turns a drive through Dudhwa into a reading of one of India's most remarkable ecosystems.