Invasive weed threatens elephant habitats in Tamil Nadu

An invasion of Ludwigia peruviana over the last decade is suppressing edible forage for elephants, gaurs and other herbivores, increasing the risk of man-animal conflict in the area

July 22, 2023 11:43 pm | Updated July 24, 2023 01:29 pm IST - COIMBATORE

An elephant herd with a calf at a swamp with aquatic weed Ludwigia peruviana at Valparai in Tamil Nadu’s Coimbatore district

An elephant herd with a calf at a swamp with aquatic weed Ludwigia peruviana at Valparai in Tamil Nadu’s Coimbatore district | Photo Credit: Ganesh Raghunathan, Nature Conservation Foundation

An aquatic weed native to some countries in Central and South America, including Peru, is threatening elephant habitats and foraging areas in Valparai, a Tamil Nadu hill station close to the Kerala border, and reviving the risk of human-elephant conflicts in the region.

Ludwigia peruviana, which grows fast along water bodies, has infested the majority of the hill station’s swamps, locally known as vayals, where elephants used to find lush grass even in the summer. However, the Forest Department says that most of these swamps are located in private estates, which are responsible for the tricky process of removing the weed; if not done correctly, trying to pull it out will simply help it spread even more.

Suppressing forage

The rapid large-scale spread of the weed — which was probably intrduced as an ornamental plant for its tiny yellow flowers — has shaken the balance of these perennial foraging grounds, limiting the growth of grass and native plants that are palatable to elephants and other animals including gaur.

Ludwigia peruviana

Ludwigia peruviana | Photo Credit: Special Arrangement

T.R. Shankar Raman, wildlife scientist with the Nature Conservation Foundation (NCF) in Valparai, has been watching the weed’s increasing spread over the past five years. “It mainly spreads along the swamps in the middle of the tea estates and forms thickets. These swamps are known for excellent grass covers, sedges and water sources that are very good for herbivores like gaur and elephant in particular,” he says. Even in the dry months, one could find some water in the valley and grasses and sedges all along the swamps, but the dense thickets of Ludwigia now suppress such edible forage. “Now as there is no forage, it is likely that they may come in closer contact with people,” explains Mr. Raman.

Losing pachyderm habitats

Located within the Annamalai Tiger Reserve, Valparai’s mosaic landscape of tea estates and fragmented forest patches still serve as key habitats for the elephants that move between Tamil Nadu and Kerala. The hill station, which used to be a terrain known for human-elephant conflicts, has seen a difference due to the joint efforts of the Forest Department’s rapid response team and NCF’s early warning system. The last human death due to elephant attack on the plateau occurred more than two years ago, on June 4, 2021.

The NCF, which has over two decades of experience in Valparai, has been flagging the Ludwigia invasion to the Forest Department and estate managements.

“Swamps are unique habitats that support amphibians and otters besides the large herbivores. They act as water storage areas that need to be preserved. If Ludwigia colonises, it completely chokes swamps and does not allow grasses to grow. The wildlife that had been depending on such swamps will move to other areas and it might lead to negative interactions,” says Srinivasan Kasinathan, restoration ecologist and senior programme manager with NCF.

Ganesh Raghunathan, another NCF senior programme manager, recalls that Ludwigia had a very minimal presence in Valparai’s swamps when he joined the NCF as a researcher in 2011. “Now, some of the swamps have disappeared due to its invasion,” he says.

‘Private estates’ responsibility’

Though Ludwigia is among the 22 priority invasive plants in Tamil Nadu, the State’s drive to remove exotic species from its forests is now largely focused on Lantana camara, Senna spectabilis and Acacia mearnsii (wattle).

Women plucking tea leaves as an elephant and a gaur graze in a swamp at Valparai.

Women plucking tea leaves as an elephant and a gaur graze in a swamp at Valparai. | Photo Credit: Ganesh Raghunathan, Nature Conservation Foundation

“The spread of Ludwigia has come to the Department’s attention. Most of these swamps are located in private estates. Estate managements have an obligation to do conservation activities under the Tamil Nadu Preservation of Private Forests Act. The Department will give them appropriate directions,” says S. Ramasubramanian, Conservator of Forests and chairperson for the District Level Implementation Committee for invasive species.

Risky removal

Unlike other invasive plants, Ludwigia poses a unique challenge as it grows in swamps and there is little scope to use machinery which may further destroy the ecosystem. Even if Ludwigia is pulled out manually, the soft plant easily breaks and it spreads again from the root or broken stems that fall in the swamp.

Mr. Raman says there is an urgent need to map all the swamps in Valparai, grading them as heavily invaded, invaded, getting invaded, or free of Ludwigia. “Not all the swamps are invaded and some swamps are heavily invaded and it is difficult to tackle them. There are some swamps where it is just coming in with just a few clumps. The focus should be on containing the spread by preventing invasion in swamps where smaller numbers are coming up,” he adds.

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