‘Alien vs native:’ A silent threat spreads fast in Wayanad Wildlife Sanctuary

Grown-up senna in the Muthanga range of Wayanad Wildlife Sanctuary. Photo: P A Vinayan

Wayanad: T S Eliot’s words, “This is the way the world ends, not with a bang but with a whimper,” resonate in the heart of the Nilgiri Biosphere Reserve (NBR), where the Wayanad Wildlife Sanctuary (WWS) is battling the encroachment of alien plant species. These invasive plants are rapidly spreading, displacing native flora and disrupting the delicate ecosystem.

Several alien species have been identified as major threats, including Senna spectabilis (locally known as 'manjakonna'), Lantana camara (a toxic shrub), Mikania micrantha (an invasive vine), and various Acacia species. These invasive plants not only alienate herbivores and carnivores from their natural habitat but also contribute to human-animal conflicts. Even the once-rich grasslands have succumbed to the aggressive growth of Senna.

Botanists warn that this problem extends beyond Wayanad and affects major wildlife zones in South India, such as Nagarhole and Bandipur Tiger Reserves in Karnataka, Mudumalai National Park, and Sathyamangalam Wildlife Sanctuary in Tamil Nadu. Senna is particularly aggressive in invading these regions.

Mikania micrantha, known for its rapid growth, poses a serious challenge. A single stalk can produce 20,000 to 40,000 mature seeds in a season, and its young plants grow at an astonishing rate, about 8 to 9 cm in 24 hours. Furthermore, this weed forms a dense cover over leafy stems, using trees as support.

Team forest fist with 40ft long Senna Lateral root. Photo: Forest First Samithy

The Nilgiri Biosphere Reserve, designated a Global Biodiversity Hotspot by UNESCO in 1986, is home to over 3,700 known species and a significant population of Asian elephants, making it a critical conservation area.

Only 10 Years to Save WWS
A recent study conducted by the Ferns Nature Conservation Society in collaboration with the Department of Forests and Wildlife reveals alarming statistics. By now, more than 35 per cent of the WWS (approximately 123.86 square kilometres), have been occupied by these invasive species. Among the affected areas, 18.61 sq km are densely infested, while 9.46 sq km have a lower spread. High levels of invasion are observed in Tholpetty, Muthanga, Sulthan Bathery, and Kurichiat.

The distribution of Senna in 2013-2014 in the Wayanad Wildlife Sanctuary

According to P A Vinayan, researcher and president of Ferns, the spread of Senna has increased from just 16 sq km in 2013 to a staggering 123.86 sq km in 2023. If this trend continues, the entire WWS will be infested within a decade, with one-third becoming dense Senna forest. Traditional methods, including the use of heavy machinery or chemicals, have proven ineffective and ecologically damaging.

The Senna plant, with its prolific seed production and rapid growth, poses a severe threat. A single pod contains 103 seeds, and a medium-sized tree can produce a minimum of one lakh seeds. As a result, there are approximately 30 lakh flowering Senna trees in the sanctuary, ensuring rapid expansion.

The distribution of Senna in 2022-2023 in the Wayanad Wildlife Sanctuary.

Forest Department’s misstep
The Forest Department inadvertently contributed to the problem. In 1986, they planted Senna seeds in their nursery at Ponkuzhi, near Muthanga, thinking it was a harmless flowering species. It took more than two decades for them to realise that Senna was an invasive species. The department even planted these trees as ornamental additions in eco-tourism centres and the hinterlands of WWS.

Debarking of Senna plants. Photo: PA Vinayan

Efforts to correct the mistake included cutting, pruning, debarking, and applying kerosene to the debarked portions. However, these attempts failed, as countless sprouts emerged from lateral roots and seeds.

Wildlife and environmental impact
The invasive species have severely impacted the wildlife and forest ecosystem. Mananthavady-Kutta road, passing through the sanctuary, now is rife with the dominance of Senna, replacing other vegetation. Animal populations, including deer and elephant herds, have declined. The Wayanad landscape’s tiger population has also dwindled from 120 unique tigers in 2018 to only 84 in 2023, indicating a shift in search of better prey availability.

Wildlife photographers note a decline in forest quality and animal sightings, making it harder to capture captivating moments. Animals are shifting away from Senna-infested areas, where the plant monopolises soil, stifling the growth of other vital species such as grass and bamboo. This shift has resulted in fewer animal raids, especially by herds of elephants and deer, into human habitats on the jungle’s fringes.

An elephant in the Senna-infested spot in Wayanad Wildlife Sanctuary. Photo: PA Vinayan

Data from the WWS warden’s office in Sulthan Bathery reflects this decline. Reports of crop damage by animals have decreased significantly, along with a reduction in cattle lifting cases. Senna's bitter taste and bark’s burning sensation discourage animals from consuming it.

Over the past three years, there has been a significant decline in the number of compensation applications from farmers, indicating a decrease in animal raids. In 2021-22, there were 734 reported cases of crop damage in the border agrarian hamlets of WWS. However, in the following year, 2022-23, this number dropped to 475. In the current year (2023-24), only 93 cases have been reported so far. Similarly, instances of cattle lifting in these border hamlets have also seen a decline, falling from 83 cases in 2021-22 to 19 in 2023-24. 

N Badusha, the president of Wayanad Prakrithi Samrakshana Samithi, said: “The leaves of Senna have a sour taste, and its bark can cause a burning sensation, which deters animals. We have been advocating this for many years, but the Forest Department has only recently come to realise it.” The current condition of the protected jungle areas in NBR serves as an example of negligent forest management, Badusha said.

Mitigation efforts and projects
To combat this threat, the Forest Department initiated a ‘Senna Eradication and Forest Regeneration Project’ worth Rs 5.31 crore, with support from the National Bank for Agriculture and Rural Development (NABARD). This project is currently underway in the Kurichiat and Muthanga forest ranges, targeting 1,672 hectares for Senna eradication. However, the success of this experimental effort may take up to five years to become evident.

Kerala Minister for Forests and Wildlife AK Saseendran had told the Assembly that Rs 2.67 crore had been allocated for ‘Mission Senna.’ The Kerala government had allocated Rs 46 crores to the Forest Department for Senna eradication. 

Adopting strategies from Tamil Nadu
In light of the relentless spread of Senna, the WWS is considering involving the newsprint industry, following the Tamil Nadu model. The Tamil Nadu government allows the Tamil Nadu Newsprint and Papers Ltd (TNPL) to remove invasive trees like wattles and senna from around 42,000 hectares of forest land for paper manufacturing. TNPL pays the Forest Department Rs 350 per ton for the harvested trees and employs various techniques, including winch pulling and smart machines.

The Forest First Samithi (FFS), an NGO led by professionals and supported by a 45-member tribal workforce, is actively participating in Senna eradication efforts in the Tholpetty Forest Range of WWS. They have successfully removed Senna from more than 160 acres of forest land in the past three years. However, complete eradication will require two to five years, as Senna seeds continue to sprout. The FFS advocates the use of handheld tools to minimise disturbance to the ecosystem.

A call to action
While the general public may not be fully aware of this issue, it is imperative for those closely connected to nature to recognize the urgency of the situation. Many organisations are working alongside the Forest Department in this mission, but the extent of the threat posed by these alien species demands a transparent and comprehensive action plan to curtail their spread and reduce their impact on our precious forests.

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