Latest revision as of 20:41, 26 December 2024

[edit] Invasive species

[edit] Lantana camara

Shantha Thiagarajan, Sep 9, 2024: The Times of India

Mudumalai Tiger Reserve (MTR) in the Nilgiris
From: Shantha Thiagarajan, Sep 9, 2024: The Times of India

See graphic:

Mudumalai Tiger Reserve (MTR) in the Nilgiris

It’s hard to believe that one of the biggest threats to a tiger’s survival could come from a small, beautiful flower. Yet, Lantana camara, a tropical American shrub, has invaded over 40% of India’s tiger range, with the Shivalik hills, Central India, and the Southern Western Ghats being the worst affected.


Introduced by the British in the 1800s as an ornamental plant from Latin America, the weed quickly spread across the country. By 2020, it was estimated to occupy more than 40% of India’s tiger habitats. 
 Mudumalai Tiger Reserve (MTR) in the Nilgiris, home to more than 100 tigers, has also suffered from Lantana invasion, which has led to a decline in vegetation and green patches in its core and buffer zones. That’s when the question arose: Is MTR a dying forest?


But then, in the last year, there has been a sudden transformation. Shoots of indigenous species began sprouting across the reserve, and the forest seems to be experiencing a complete regeneration of vegetation. Wildlife officials say the recovery is due to concerted efforts to remove the invasive weeds, which helped restore the ecosystem.


The MTR comprises 32,100 hectares of core zone across six ranges, with an additional 36,700 hectares in the buffer zone spread over four ranges. Faced with a threat to the ecosystem, invasive and exotic species such as Lantana camara, Senna spectabilis, Prosopis juliflora and wattle are being removed. While the buffer zone— a shrub forest—is infested with various invasives, the core zone, a dense forest, is overrun by Lantana. The process of removing these invasives began in early 2022.


In the buffer zone of MTR, about 20% of the area is encroached by invasive species, while the core zone sees at least 50% occupied mainly by Lantana. “Continuous removal of invasives has led to regeneration of natural grass and other indigenous species,” says D Venkatesh, conservator of forests and field director of MTR. “We maintain the cleared areas, but this process needs to continue for five years for the forest to be free from invasives.” He adds that while the invasives are initially fully uprooted, seeds or small roots left behind pose a threat as their dormancy period can last up to 50 years, potentially allowing them to sprout again even decades later.


Lantana camara is a perennial shrub that grows about 2m-5m tall and forms dense thickets in various environments. “Lantana is the primary invasive species in MTR, suppressing the natural regeneration of grasses and indigenous species. Once it’s cleared, removing secondary invasives becomes easier,” says Venkatesh. 


MTR is home to 25 species of grasses and legumes, including a protein-rich variety of grass. “Wild animals help spread the seeds of these species across the forest, maintaining a natural cycle facilitated by wildlife in any forest land,” says Venkatesh.


“Even after uprooting invasives, the forest will witness subsequent resprouting,” says Arun Kumar, deputy director of MTR-buffer zone. “This makes maintenance important. Without it, the initial efforts would be utterly wasted. The health of the habitat is important as regenerated grasslands attract herbivores, both small and large.”


The forest department has identified key passages in the reserve for invasive removal. Arun Kumar says in the expansive 50-hectare area of the Singara range, where invasive removal has been done and second-year maintenance is underway, herds of elephants are frequently attracted by the fresh grasses. “The health of a forest triggers a chain reaction in the ecosystem. The natural regeneration of grasses and legumes can help reduce conflicts in fringe areas, as a healthy habitat tends to keep animals within their boundaries.”
 Tamil Nadu Newsprint & Paper Limited is involved in removing Senna spectabilis species, which is found in the buffer zone of MTR. “The bark of Senna is so resilient that even a small piece left behind can quickly resprout. Therefore, extra care is needed during the removal process,” he adds.


C Vidhya, deputy director of the MTR-core zone, says the Senna species has only a scattered presence in MTR’s core area. “The real issue is Lantana. But we can’t say Lantana is all bad. It also provides ambush cover for carnivores and fruits for birds and monkeys. In some ways, it plays an eco-friendly role too. If we focus solely on tigers and herbivores, Lantana appears to be a threat.”
Vidhya says 50% of the core area is infested with Lantana. “Our fight against Lantana focuses on crucial animal passages and riverines, ensuring removal does not open up the forest too fully. Riverines and water bodies are lifelines for animals during summer, and must be preserved.”


The forest department has conducted individual assessments of every grid-compartment in the core zone. Officials say since herbivores don’t consume much Lantana, they don’t contribute to its propagation. Instead, Lantana fruits are primarily dispersed by birds and monkeys. After passing through their digestive systems, the seeds become even more viable, with a stronger tendency to sprout than through natural spread.


Vidhya confirms the flourishing of grass and indigenous species is a direct result of Lantana removal. “When you remove invasive species, the ecosystem undergoes modifications, increasing the carrying capacity and utility index of the grasslands,” says Gajannan D Muratkar, advisor to 39 tiger reserves, including MTR and environmental science professor at Amaravathi University in Maharashtra. “An interconnected ecosystem forms between grasslands, modifying the diversity index of the ground flora. It helps contain small and large herbivores within these pockets.”


Uprooting invasive species also corrects soil features such as moisture, colour and texture. The natural regeneration of grasses reflects the improved quality of the soil, he says.


For Lantana removal, the forest department relies on local tribal communities, skilled in the techniques needed for this task. However, the department struggles with limited funds for the removal efforts, often using money generated from selling Senna species to support the work.


In the core zone, 1,221 hectares have been identified as critical for Lantana removal, with about 355 hectares—29%—cleared. In the buffer zone, 1,615 hectares have been cleared and maintained into the second year. The process progresses stage by stage in other areas as well. “We’re seeing amazing results. Once fully completed, the forest ecosystem will sustain itself and support the wildlife,” says Venkatesh.

[edit] Senna spectabilis/ Strategies to halt spread

Rohan Premkumar, Nov 1, 2022: The Hindu

Strategies planned to halt spread of invasive species over 800 hectares of Mudumalai Tiger Reserve buffer zone

Appearing to spread faster over the last five years, the invasive weed has a negative effect on local biodiversity

An invasive species, Senna spectabilis, an exotic tree, has taken over between 800 and 1,200 hectares of the buffer zones of the Mudumalai Tiger Reserve (MTR) in the picturesque Nilgiris hill district. The Forest Department is coming up with a comprehensive strategy to deal with the spread of the invasive species, which continues to spread rapidly in the buffer zone.

Introduced as an ornamental species and for use as firewood from South and Central America, the species has become highly invasive in the Sigur plateau in both the core and buffer zones of the MTR.

Over the last few years, its bright yellow flowers have become more visible across the Tiger Reserve, with conservationists stating that the invasive weed has a negative effect on local biodiversity, crowding out native species and limiting food availability for wildlife.

According to P. Arunkumar, Deputy Director, MTR (Buffer Zone), the Forest Department estimates that the species has spread over 800-1,200 hectares of the buffer zone.

Local residents said they had noticed the species seemed to be spreading faster over the last five years, during which time the trees seem to have become more common.

The Forest Department is still demarcating areas where the species is spreading, but officials stated that they were looking at ensuring that the removal of the trees begins before the problem becomes more difficult to manage.

According to officials, policy-level discussions are under way on the Tamil Nadu Newsprint and Papers Limited (TNPL) plan to use wood from Senna spectabilis from the MTR for paper-making. They said the funds so raised would be used in eco-restoration to bring back native species.

Mr. Arunkumar said that the Forest Department was also formulating a 10-year-plan to systematically remove Lantana camara, the other major weed that poses a threat to biodiversity in both the core and buffer zones of the Tiger Reserve.

Senna spectabilis, along with Lantana camara, is among five major invasive weeds that had taken over vast swathes of the Nilgiris, with wattle being the other major invasive species. Eucalyptus and pine, though exotic, do not spread as quickly as the other species and are considered easier to manage, Forest Department officials said.

Officials also stated that the Madras High Court was hearing petitions calling for the removal of exotic species, and that judges from the court had inspected the Tiger Reserve this year to monitor progress in the removal of invasive species.

Top Forest Department officials said that Senna spectabilis was spreading fastest in the Singara and Masinagudi forest ranges in the MTR buffer zone, as well as in Kargudi range in the core area of the reserve. They said that policy-level decisions are being formulated that will allow the TNPL to remove the species from the landscape. They added that 125 hectares of Lantana camara was removed in 2021, and that 70 hectares of the weed are to be removed this year.