Tamil Nadu

Alien, Invasive and thriving: Native plants choked in Western Ghats

Pine trees (in the foreground), an invasive species in the Upper Nilgiris.   | Photo Credit: M.Sathyamoorthy

Last week, the Madurai Bench of the Madras High Court, hearing a public interest litigation petition seeking the removal of invasive trees from over 22,000 hectares in the Western Ghats here, directed the National Board for Wildlife to look into the issue and pass appropriate orders.


While invasive species of flora like eucalyptus, wattle, pine and cypress trees, as well as Lantana camara plants, are proliferating across the Nilgiris upper slopes, Prosopis juliflora, parthenium and eupatorium have spread ón the biosphere’s lower slopes, forest officials said.

Weeds like scotch broom (Cytisus scoparius) and gorse have also begun to spread profusely in habitats like Avalanche, Upper Bhavani and the Mukurthi National Park, home to the endangered Nilgiri tahr, the State animal.

More research

B. Ramakrishnan, assistant professor, Department of Wildlife Biology, Udhagamandalam Government Arts College, said, “Scotch broom and gorse have taken over vast expanses of grasslands which used to serve as grazing lands for the Nilgiri tahr. During the census conducted this year, we found that the animals were actually eating the plants,” he said, adding that more research needs to be done to understand whether the consumption of the invasive weeds could have an impact on the health of ungulates like the tahr in the long run.


The Forest Department has taken measures to deal with the spread of the invasive flora over the last few years, with mixed results. Sumesh Soman, District Forest Officer, Nilgiris Division, said that wattle and eucalyptus have been removed in Korakundah, Parsons Valley, Avalanche and Kodanad.

“We have noticed that grasslands have shown signs of regeneration in these areas, especially Korakundah and Parsons Valley,” said Mr. Soman, adding that removal of wattle is a tougher task than the removal of other species from the landscape.

“The wattle trees flower abundantly, and seeds from each tree number in the hundreds of thousands. Removing each tree is not enough, as we have to remove fresh sprouts from the seeds left behind over a 4-5 year period to aid the native tree species to take root in any patch,” he added.

Mudumalai Tiger Reserve too has been impacted by the spread of invasive plants, especially Lantana camara and parthenium. Deputy Director of the Mudumalai Tiger Reserve (MTR), S. Senbagapriya, said that around 70% of the tiger reserve has been taken over by lantana, leading to a diminishing fodder base for herbivores within the reserve.

“This year, we have removed lantana from around 300 hectares of forest, and as we do maintenance work on the patches of forest where the invasive species were removed from previous years, we have noticed fresh grasslands developing,” said Ms. Senbagapriya, who added that artisans from the tribal communities living in the reserve had been encouraged to produce furniture from the lantana plants in the past.

“However, due to a lack of buyers for the furniture, it has simply not been viable for the communities to produce the furniture,” she said.

Impact on biodiversity

While invasive species of flora have had an impact on biodiversity in the Nilgiris, restoration ecologists and experts who have worked in the region for many years have urged caution in dealing with their removal.

Restoration ecologist Vasanth Bosco, who has restored grasslands and Shola patches in a few places, said, “Large-scale removal of invasive plant and tree species from the Nilgiris is not a good idea.” “Restoration efforts should be small in scale, with a view to facilitating the native species thrive in their habitat and spread by themselves.

A better strategy would be to preserve the Shola and grassland ecosystems which already exist, and concentrate on restoring small areas,” he said.

The Forest Department has been working to eradicate invasive species in the Nilgiris and elsewhere in the State for many years now. The department needs funds, manpower and persistence.

“It has to be a continuous exercise for at least 10 years for results to show. As the invasive species have been there for three to four decades, it is not easy to remove them completely. For instance, Prosopis juliflora can spread through the fecal matter of the wild animals,” said a forest official. First, the larger trees have to be cut, then followed up by cleaning up the new trees for years together, he added. Wherever the forest department has been persistent, the results have shown that the native species have begun to thrive.

N. Arun Shankar, an activist from Dindigul associated with the Tamil Nadu Green Movement, remembers the time when he and his friends travelled from Munnar to Kodaikanal via Top Station on New Year’s eve in 1987.

“Today, that route is almost unusable due to the invasion of exotic and non-native trees, particularly the wattle,” he said, adding that the wattle along with eucalyptus and pine has become an insurmountable ecological challenge in the Kodaikanal Wildlife Sanctuary, Meghamalai Wildlife Sanctuary and adjoining forests in the Western Ghats by affecting the survival and regeneration of Shola and montane grasslands.

Pointing out that these invasive trees were introduced by the British and later even by the Indian government to support industries and for firewood, Mr. Shankar urged the government to act fast instead of contemplating different approaches.

“A mass felling exercise of invasive trees was done in Kodaikanal around 2009-10. However, it was later stopped due to a variety of reasons including people acting with vested interests. Once Kodaikanal Wildlife Sanctuary was formed, the process was abandoned due to restriction on felling of trees,” he said.

Threat of encroachers

Another activist from Theni district, who works closely with the Forest Department, also highlighted the phenomenon of encroachers in forest areas growing cashew trees and few other varieties for monetary benefits along the Western Ghats in Theni and Dindigul districts .

“The problem cannot be underestimated since it also affects the ecology. Stringent action must be taken against encroachers,” he said.

According to activists, a coordinated effort in mission mode involving different departments and the Kerala forest department can address the issue in Theni and Dindigul districts of the Western Ghats to an extent.

While acknowledging the need for swift action, T.S. Subramaniya Raja, a conservationist from Virudhunagar district, stresses on a cautious approach. “We should not worsen the situation or create different problems. Such exercises must be done on a pilot basis in select areas and expanded later,” he said.

He explained that the problem of invasive trees was not as severe in places like Grizzled Squirrel Wildlife Sanctuary, Srivilliputhur or the Kalakkad Mundanthurai Tiger Reserve.

“Perhaps the reason is that the British did not show much interest in these places as they did in Kodaikanal and Ooty,” he said.

Wildlife continues to thrive in the Western Ghats, including the Nilgiris biosphere, despite the invasive species, said a forest official. But he admitted that the benefits to the native system from the alien species was low.

"It [eradication of invasive species] is not as easy as is being said," said a former Principal Chief Conservator of Forests and Head of the State Forest Department. "We have attempted large-scale felling, as in Kodaikanal. We have tried replanting also. But you can't do a thousand hectares in a year," he added.

The Forest Department has also tried cutting and clipping branches but has found there has been a regeneration in most cases. In some cases, even scrap-weeding has not helped as the seeds of the invasive species that have fallen have sprouted, he said.

"Weedicides can't be used because of the rich biodiversity of our forests. Now bio-weedicides have come but more research and funding for actual operations on the ground are required," he said.

A growing problem

Invasive species in the forest ecosystems of Tamil Nadu have resulted in a loss of biodiversity, with an adverse impact on the ecology and economy. A lowdown ont he threat posed by them:

  • Invasive species do not allow any shrub or local species of grass to grow around them.
  • They grow in dense fashion, leaving little space for wildlife to pass through.
  • A resin oozes from some species during the monsoon, which turns the soil acidic.
  • Invasive species like Lantana spread all over an area and create a mat-like structure. They lead to retrogression and a change in the original vegetation in the longer run, degrading and destroying biodiversity. In the proce3ss, herbivores such as the Indian gaur, spotted deer and sambar do not get the required grass, shrubs and plants they feed on. If the herbivores are affected, carnivores like tigers and panthers also suffer.
  • Some of the invasive trees are not deep rooted and get easily uprooted during storms and fall on roads, creating problems for users.
  • Apart from other factors, monoculture plantation of eucalyptus and wattle could endanger the Nilgiri tahr as it could affect the heart of its habitat, the grasslands.
  • They can lead to the movement of wildlife. The Indian gaur population from the wild has started migrating to Kodaikanal town in search of fodder. It is a major problem in areas such as Thadiyankudisai, Thandikudi, Pannaikkadu and Kmbarayur as well.

(With inputs from B. Aravind Kumar)

Our code of editorial values

This article is closed for comments.
Please Email the Editor

Printable version | Sep 24, 2021 3:27:50 AM | https://www.thehindu.com/news/national/tamil-nadu/alien-invasive-and-thriving/article24905530.ece

Next Story