Manas Saved Its Tigers and Lost Its Grass: The Habitat Nobody Counts
Grassland cover in the World Heritage reserve fell from 53.61% to 30.24% in 29 years — a collapse driven by invasive plants, not poachers
What happened
Conservation success in India is almost always reported as an animal count. Manas is the case that exposes what that metric misses: the reserve's flagship populations recovered, and simultaneously more than two-fifths of its grassland vanished. For an answer on biodiversity, this is the sharpest available illustration of why habitat quality and species numbers can move in opposite directions — and why India's grasslands, still classified in much revenue usage as 'wasteland', are its most neglected biome.
Manas Grassland Cover, 1990 vs 2019
Share of Reserve Under Grassland
| Absolute loss | 23.37 percentage points |
| Relative decline | ~43.6% |
| Period | 29 years |
| Invasive species identified | 14 |
| Restored, 2022–25 | ~609 ha |
Source: Assam Legislative Assembly, 6 July 2026; UNESCO World Heritage Committee, June 2026
Manas lies in Assam along the Bhutan foothills, separated from Bhutan's Royal Manas National Park by the Manas river and its tributaries (Beki, Hakua), and from West Bengal's Buxa Tiger Reserve by the Sankosh river.
●It carries an unusual density of designations: UNESCO Natural World Heritage Site (inscribed 1985), Tiger Reserve, Elephant Reserve, Biosphere Reserve and Important Bird Area.
●It was placed on the List of World Heritage in Danger in 1992 following insurgency-era damage and removed only in 2011 after wildlife populations recovered.
●Its vegetation spans semi-evergreen and mixed deciduous forest, riparian fringe, Khair–Sisoo forest and — critically — alluvial savannah grassland.
●That grassland is the habitat on which the pygmy hog (Porcula salvania, Endangered), Bengal florican (Critically Endangered), hispid hare, swamp deer and greater one-horned rhinoceros depend; several of them cannot substitute forest for it.
●Survey data record grassland cover falling from 53.61 per cent (1990) to 30.24 per cent (2019). Invasive alien species are recognised under Target 6 of the Kunming–Montreal Global Biodiversity Framework and are among the leading global drivers of biodiversity loss.
Manas recovered its tigers and rhinos yet lost over two-fifths of its grassland — proof that species counts and habitat integrity can move in opposite directions, and that the metric we publicise is not the one that governs long-run survival.
◎ In Simple Words
Manas is a famous protected forest in Assam, known for tigers and rhinos. But it is not only forest — a large part of it used to be tall grassland, which is where some very rare animals live, like the tiny pygmy hog and the Bengal florican bird. Over about thirty years, more than two-fifths of that grassland has disappeared. The main reason is not hunting: it is foreign weeds that spread fast, smother the native grass and turn open grassland into scrub. The state government told the Assembly it has begun replanting grass to bring it back.
Factual Pointers
Practice · 2 questions
With reference to Manas Wildlife Sanctuary, consider the following statements:
1. It is a UNESCO World Heritage Site that was placed on the List of World Heritage in Danger and later removed from it.
2. It is contiguous with the Royal Manas National Park of Bhutan.
3. It is the release site for the conservation breeding programme of the pygmy hog.
Which of the statements given above are correct?
Chromolaena odorata and Mikania micrantha, sometimes in the news, are best described as:
Mains Practice Questions
"Species recovery and habitat integrity can move in opposite directions." Critically examine this proposition using the case of grassland loss in Manas, and suggest reforms to conservation monitoring. (250 words, GS3)
Invasive alien species pose a threat that protected-area law in India is poorly equipped to counter. Discuss. (250 words, GS3)
India's grasslands remain classified and treated as 'wastelands'. Examine the ecological and policy consequences of this classification. (150 words, GS3)
Frequently Asked
· People also askHow much grassland has Manas lost?
Grassland cover fell from 53.61 per cent of the reserve in 1990 to 30.24 per cent in 2019 — an absolute reduction of 23.37 percentage points and a relative decline of roughly 43.6 per cent over 29 years. Fourteen invasive plant species were identified among the principal drivers.
Prelims · GS3The figures were placed before the Assam Legislative Assembly on 6 July 2026. The UNESCO World Heritage Committee separately flagged continuing invasive-species impact on the property in June 2026.
SOURCE The Assam Tribune; Assam Legislative Assembly
Which invasive species are damaging Manas?
Chromolaena odorata (Siam weed) and Mikania micrantha (mile-a-minute weed) are among the principal invaders. Both are fast-spreading neotropical plants that smother native grasses, suppress regeneration and accelerate woody encroachment, converting open savannah grassland into scrub.
Prelims · GS3Fourteen invasive species in total were identified. Invasive alien species are one of the five direct drivers of biodiversity loss identified by IPBES and the subject of Target 6 of the Kunming–Montreal Global Biodiversity Framework.
SOURCE Assam Forest Department; IPBES
Why do grasslands matter more than forest at Manas?
Several of the reserve's rarest species are grassland obligates that cannot use forest: the pygmy hog (Endangered), Bengal florican (Critically Endangered) and hispid hare. For them canopy closure is not a change of habitat but the loss of it, so grassland decline is potentially existential rather than proportionate harm.
GS3 · EnvironmentSwamp deer and the greater one-horned rhinoceros also depend heavily on grassland for grazing. Generalists such as the tiger — the species public metrics track — are comparatively unaffected, which is why the headline numbers concealed the trend.
SOURCE Pygmy Hog Conservation Programme; IUCN
Was Manas ever on the List of World Heritage in Danger?
Yes. Manas was inscribed as a UNESCO Natural World Heritage Site in 1985, placed on the List of World Heritage in Danger in 1992 following insurgency-era damage, and removed from that list in 2011 after tiger and rhino populations recovered.
Prelims · GS1Grassland cover continued declining throughout that recovery period — meaning the species-based criteria used to certify delisting did not capture the habitat trend running beneath it.
SOURCE UNESCO World Heritage Centre
What is Assam doing to restore the grasslands?
The state told the Assembly that about 609 hectares of degraded grassland were restored between 2022 and 2025 under the French-funded APFPC project and the Pygmy Hog Conservation Programme, alongside grass nursery and native-species replanting efforts.
GS3 · GovernanceThe Assembly Speaker cautioned that invasive removal must not damage indigenous vegetation — a real operational risk, since mechanical or chemical clearing can degrade the native seed bank it is meant to release.
SOURCE Assam Forest Department; The Assam Tribune
Why is invasive species control hard under Indian wildlife law?
The Wild Life (Protection) Act, 1972 is built around prohibiting human actions — hunting, encroachment, land diversion — and its instruments are regulatory. An invasion is an autonomous ecological process that continues inside a perfectly enforced sanctuary, so protection from people is not protection from Chromolaena.
GS3 · Environmental LawCountering it needs sustained, decade-scale ecological management funding, whereas conservation budgets are structured around annual, project-shaped allocations. India has no dedicated funding line for invasive control in protected areas.
SOURCE Wild Life (Protection) Act, 1972
Where is Manas located and what does it adjoin?
Manas lies in Assam along the Bhutan foothills. It is contiguous with Bhutan's Royal Manas National Park across the Manas river and its tributaries (Beki, Hakua), and is separated from West Bengal's Buxa Tiger Reserve by the Sankosh river.
Prelims · GeographyThis makes it a transboundary conservation landscape: wildlife movement, river regimes and invasive spread all cross the India–Bhutan border, so effective management requires bilateral coordination rather than parallel national efforts.
SOURCE UNESCO World Heritage Centre