Manas Tiger Reserve in western Assam is, by most conservation metrics, a genuine success story: zero rhino and tiger poaching for three consecutive years, a tiger population that has climbed to 57 individuals with an increasing density trend since 2006, and a rhino population that has held steady in the high 40s after decades of recovery from the insurgency-era devastation that once nearly wiped the park's wildlife out. Yet the same reserve is losing the specific habitat that much of that wildlife depends on. Forest Department data under the Bodoland Territorial Council shows Manas's grassland cover has shrunk from 53.61% of the reserve's area in 1990 to just 30.24% in 2019 — a drop severe enough that UNESCO's World Heritage Committee has formally flagged it as a concern for the property's long-term ecological integrity.
The paradox at the heart of Manas today is that anti-poaching success and habitat decline can occur simultaneously, driven by entirely different causes. Poaching has been suppressed through better patrolling, community engagement and sustained political will following the return of stability to the Bodoland region after decades of insurgency-linked disruption. Grassland loss, by contrast, is an ecological process — invasive plant species outcompeting native grasses, changing fire regimes, and shifts in large-herbivore grazing pressure — that does not respond to the same law-enforcement tools that ended poaching.
Background
Manas has one of the more dramatic conservation turnaround stories in Indian wildlife management. The reserve, which straddles the India-Bhutan border in western Assam, was pushed to the brink during the Bodo insurgency of the 1990s and 2000s, when years of civil unrest devastated wildlife populations and infrastructure inside the park, leading UNESCO to place Manas Wildlife Sanctuary on its List of World Heritage in Danger. Steady conservation investment following the restoration of stability in the region eventually earned Manas removal from that danger list in 2011, and the two decades since have seen a genuine recovery in flagship species populations — most visibly tigers and rhinos, and more quietly, a slower reintroduction effort for the critically endangered pygmy hog, one of the world's smallest and rarest wild pig species.
Even as those population numbers have recovered, the underlying grassland ecosystem that many of Manas's most vulnerable and specialised species depend on has been eroding in the background. Grasslands are not simply empty space between forest patches — they are among the most biodiverse and threatened habitat types in India, hosting species like the pygmy hog, hispid hare, Bengal florican and various grassland-specialist birds that cannot survive in either dense forest or degraded scrub. When grassland converts to woodland or gets overrun by invasive weed species, these habitat specialists lose viable territory even in a park where overall wildlife numbers are rising.
Key Details
- Grassland decline: From 53.61% of the reserve's area in 1990 to 30.24% in 2019 — a 43.59% relative decline, according to Bodoland Territorial Council Forest Department data.
- Primary driver: Invasive plant species, particularly Chromolaena odorata and Mikania micrantha, which outcompete native grasses, reduce biodiversity and alter the ecosystem's natural fire and grazing dynamics.
- Secondary drivers: Uncontrolled forest fires, indiscriminate livestock grazing by domestic animals, and a gradual decline in natural browsing/grazing pressure from wild large herbivores, which together accelerate the conversion of open grassland into woodland.
- UNESCO concern: The World Heritage Committee has flagged that invasive species continue to affect the grassland-woodland ecosystem balance at the property, noting that close to half of Manas's grasslands have been lost.
- Poaching record: Zero rhino and tiger poaching recorded for three consecutive years, a milestone Chief Minister Himanta Biswa Sarma has publicly cited as a major conservation achievement.
- Tiger population: 57 individuals recorded in the most recent national tiger status assessment, with an increasing population and density trend since 2006.
- Rhino population: 38 (2020-21), 40 (2021-22) and 47 (2022-23) individuals — a stable-to-growing trend attributed to strengthened protection.
- Pygmy hog reintroduction: 54 individuals reintroduced to date as of 2023, working toward a target of 60 released hogs.
- Overall biodiversity: Manas hosts nearly 60 mammal species, 42 reptile species, seven amphibian species and around 500 bird species, of which 26 are globally threatened, alongside rare species including the red panda, golden langur, Assam roofed turtle and hispid hare.
At a Glance
| Metric | 1990 | 2019 / Latest |
|---|---|---|
| Grassland cover | 53.61% of reserve area | 30.24% of reserve area |
| Tiger population | Historically depleted (insurgency era) | 57 individuals (rising trend since 2006) |
| Rhino population | Near-extirpated (insurgency era) | 47 individuals (2022-23) |
| Poaching incidents | Severe, ongoing during unrest | Zero for 3 consecutive years |
| UNESCO status | World Heritage in Danger (until 2011) | Removed from danger list; grassland loss flagged as ongoing concern |
| Pygmy hog reintroduction | Not yet started | 54 of 60 target released (as of 2023) |
Local Impact
For the Bodoland region, Manas's dual identity — a poaching-free success story that is simultaneously an ecosystem in slow decline — carries real stakes beyond conservation science. The Bodoland Territorial Council has invested heavily in positioning Manas as an eco-tourism draw, part of a broader post-conflict economic development strategy for a region still working to rebuild its reputation and economy after decades of insurgency. A degrading grassland ecosystem threatens the very wildlife spectacle — grazing rhinos, open-country tiger sightings, grassland bird diversity — that eco-tourism in Manas depends on, even as headline species population numbers continue to look strong.
The invasive species driving grassland loss, Chromolaena odorata and Mikania micrantha in particular, are notoriously difficult and labour-intensive to control once established, often requiring repeated manual clearing, controlled grazing management or fire regime interventions rather than one-time removal efforts. This makes grassland restoration a long-term, resource-intensive commitment rather than a problem that can be resolved through a single forest department initiative, putting pressure on both state and central conservation budgets.
What Happens Next
Given UNESCO's formal flagging of the grassland decline, Manas's management authorities are likely to face increased scrutiny at future World Heritage Committee reviews regarding concrete restoration measures, potentially including controlled burning programmes, invasive species removal drives, and managed grazing interventions designed to restore natural grassland-maintenance processes that historically kept woodland encroachment in check. The pygmy hog reintroduction programme's progress toward its 60-hog release target will also serve as an indirect indicator of grassland habitat quality, since the species depends specifically on tall, undisturbed grassland to survive — meaning continued success or failure of that reintroduction effort will effectively function as a barometer for whether grassland restoration efforts are gaining ground against invasive species encroachment.
Frequently Asked Questions
How much grassland has Manas Tiger Reserve lost?
Grassland cover declined from 53.61% of the reserve's area in 1990 to 30.24% in 2019 — a 43.59% relative decline over 29 years, according to Bodoland Territorial Council Forest Department data.
What is causing the grassland decline?
Primarily invasive plant species such as Chromolaena odorata and Mikania micrantha outcompeting native grasses, along with uncontrolled forest fires, livestock grazing, and reduced natural browsing pressure from wild herbivores.
Has UNESCO commented on this issue?
Yes, the World Heritage Committee has flagged ongoing concern about invasive species affecting the grassland-woodland ecosystem balance at Manas, noting close to half the grasslands have been lost.
Is Manas still on UNESCO's danger list?
No — Manas Wildlife Sanctuary was removed from the List of World Heritage in Danger in 2011 following conservation recovery after the Bodo insurgency era, though grassland loss remains a flagged ongoing concern.
How is Manas's wildlife population doing overall?
Strongly recovering in headline terms — zero rhino and tiger poaching for three consecutive years, 57 tigers with a rising trend, and 47 rhinos as of 2022-23, alongside an ongoing pygmy hog reintroduction programme.
What is the pygmy hog reintroduction programme?
An effort to reintroduce the critically endangered pygmy hog, one of the world's smallest wild pigs, to Manas's grasslands, with 54 of a 60-hog target released as of 2023.
Why does grassland loss matter if overall wildlife numbers are rising?
Grasslands host specialist species — like the pygmy hog, hispid hare and grassland birds — that cannot survive in forest or degraded scrub habitat, meaning grassland loss threatens specific vulnerable species even while more adaptable species like tigers show population growth.
Where is Manas Tiger Reserve located?
In western Assam, straddling the India-Bhutan border, within the Bodoland Territorial Council area.
Sources
Northeast News, EastMojo, The Assam Tribune, Republic World, IUCN World Heritage Outlook, UNESCO World Heritage Centre, Mongabay India.
