Green invaders: How Kaziranga is under a grave ecological threat

Guwahati: Kaziranga National Park, a UNESCO World Heritage Site famed for its one-horned rhinoceroses and sweeping grasslands, is facing a grave ecological threat — the rapid spread of invasive plant species that are altering its sensitive ecosystems.

A detailed study by the Wildlife Institute of India, conducted under the NTCA-sponsored project “Addressing the Management Issues of Kaziranga Tiger Reserve through Applied Research,” has flagged eight fast-spreading non-native plant species in Kaziranga’s floodplains. 

Using a combination of satellite modeling, field surveys, and climate projections, the researchers warned that these species could severely reshape the park’s landscape, reduce forage for herbivores, and undermine overall biodiversity.

Among the most aggressive invaders identified are Mikania micrantha (mile-a-minute weed), Parthenium hysterophorus (famine weed), and Ageratum conyzoides (billygoat weed). These plants are notorious for forming dense monocultures that smother native vegetation.

“This is a silent crisis,” stated lead author Jyotish Ranjan Deka. “These species are not only spreading now, but climate change is creating even more favorable conditions for their future expansion.”

Climate Change and Human Activity Fueling the Spread

The research employed species distribution models under two climate scenarios — a moderate (SSP2-4.5) and a high (SSP5-8.5) global warming trajectory — to forecast the spread in the years 2050 and 2070. The results are alarming. Mikania micrantha could cover up to 13% of Kaziranga’s area by 2070, while Parthenium hysterophorus and Ageratum conyzoides may each expand their range by about 6% by 2050.

However, climate change is only part of the problem. The study found that human activity plays a far greater role, contributing to 48% of the risk factors — significantly higher than climate (17%) or soil conditions (15%). Roads, tea gardens, and settlements surrounding the park are acting as corridors for these invaders.

“We were surprised by the influence of roads, tea gardens, and settlements,” said co-author Ruchi Badola. “These are acting as highways for invasive species.”

Kaziranga is ringed by more than 32 tea gardens, and a national highway runs along its southern boundary. The heavy vehicular movement, tourists, and transport of goods enable invasive plant seeds to penetrate deep into the park. The study particularly noted the prevalence of Mimosa invisa and Chromolaena odorata within 200 meters of roads, illustrating the direct link between human infrastructure and ecological vulnerability.

Impacts on Wildlife and Ecosystems

The park’s rich grasslands support a wide range of megafauna, including over 2,000 one-horned rhinoceroses, elephants, swamp deer, and wild buffaloes. The proliferation of invasive species is threatening these species’ food sources by outcompeting and replacing native grasses.

“These aren’t just weeds,” warned senior researcher Syed Ainul Hussain. “They’re ecosystem disruptors. If left unchecked, they could alter the very character of Kaziranga.”

Even native flora like Bombax species are expanding at an alarming rate, particularly in the Bagori ranges, potentially affecting the grassland biomass and the long-term survival of large herbivores that rely on open grasslands for grazing.

Wetlands, another critical feature of Kaziranga’s ecology, are also under threat. With over 250 wetlands in the park, the study noted that Mikania micrantha thrives particularly well near water bodies, adding another layer of concern to habitat preservation.

Mapping the Hotspots

One of the key achievements of the study is the creation of detailed invasion risk hotspot maps. These combine present data with projected climate scenarios and environmental variables to identify zones at risk.

The maps reveal “very high-risk zones” where multiple invasive species are predicted to flourish. They also highlight “gain areas” that are currently safe but projected to face future invasions. Additionally, the researchers identified areas most influenced by environmental variables such as soil pH, sand content, and proximity to tea gardens. These maps were cross-verified with independent field data and are intended to serve as practical tools for forest officials in planning removal and monitoring operations.

“This research will fill the information gap of documentation on habitat and will be helpful for the Kaziranga Tiger Reserve management intervention,” said Rabin Sarma, a retired research officer of Kaziranga National Park. While he personally opposes intensive intervention in Kaziranga, Sarma agreed that routine control measures are crucial in the case of invasive species.

Co-author Rashmi Das highlighted that Mikania micrantha, Chromolaena odorata, Ipomoea carnea, and Ageratum conyzoides are becoming dominant invaders, particularly in flood-prone and disturbed zones, where they are swiftly replacing native species.

Umar Saeed, another co-author, stated that he has been monitoring the encroachment of native grasslands by these species since 2018. He reiterated the urgent need for proactive monitoring and timely management to address these ecological changes before they become irreversible.

Recommendations and Next Steps

The study recommends several urgent interventions. First, it advises limiting new road construction and regulating safari vehicle movement in the park’s core areas to reduce the spread of invasive species. It also proposes integrating invasive species management into the park’s daily patrolling and maintenance protocols. High-risk areas identified in the study should be prioritized for immediate removal efforts.

Furthermore, the researchers stress the need for a user-friendly, combined invasion risk map to help forest officials make real-time decisions during conservation activities.

“Kaziranga is already battling floods, poaching, and tourism pressure. The invasion of alien plants is a slow-moving but irreversible threat if not tackled now,” the report concludes.

While this study serves as a wake-up call for Kaziranga, it also acts as a model for other protected areas across India and Asia facing similar ecological challenges. The time for intervention is now, say researchers — before the wild grasslands of Kaziranga are forever lost under a carpet of green invaders.

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