Tamil Nadu challenges spread of invasive species head on

This is the third part of a series exploring the food crisis for wildlife. Read the first part and the second part.

The dense forests of Tamil Nadu are facing a rapid spread of invasive plant species, which is upsetting the natural balance, making it challenging for wild animals to find food. However, unlike Kerala and Karnataka, which are facing the same issues, Tamil Nadu is the only state that appears to be going about systematically to contain invasive species.

Invasive alien plant species have been a long-persisted problem in the state’s forests owing to the large-scale introduction of myriad species (mostly due to commercial and socioeconomic reasons) in the past.

A 2015 analysis of invasive alien plant species in the country used ecological niche modelling (ENM), also known as species distribution modelling, to predict the distribution of species in geographic space. It found parts of Tamil Nadu, predominantly the Western Ghats, among the chief invasion hotspots.

Recognising the need to combat the menace, Tamil Nadu became the first state in the country to unveil its own comprehensive policy, the Tamil Nadu Policy on Invasive Plants and Ecological Restoration (TNPIPER), in June 2022.

The state had proposed developing this policy in September 2021. The policy aims to eradicate invasive species and restore the environment, according to Supriya Sahu, additional chief secretary for environment, climate change, and forests in Tamil Nadu.

In November 2021, under the TNPIPER, the state constituted a committee of experts who found 196 alien invasive plant species in forest areas, of which 23 were ‘priority invasives’. Of these, seven were most harmful and covered over 3.18 hectares of forest land in the state.

“Invasive alien plant species are global challenge; however, in Tamil Nadu, we have gone in a systematic way to fight this menace. The state government constituted a committee in November 2021 that released the policy, focusing on various aspects including types of invasive alien species affecting forests, methods of removal and eco-restoration. We have been aggressively working towards it for the past one-and-a-half years,” added Sahu.

The forest department began removing the top-priority invasive species, prosopis juliflora, from an elephant corridor in the state in 2021, said D Venkatesh, conservator of forests and field director, Mudumalai Tiger Reserve, Nilgiris district. The corridor comprises a village on the banks of a Bhavani river tributary, Mayar river and is surrounded by Sathyamangalam in Erode district, a protected area and tiger reserve.

The region is bordered by the Western and Eastern Ghats, as well as the Mudumalai Tiger Reserve. Elephants from Nagercoil, Wayanad and Bandipur National Park use this corridor to reach Bhavanisagar lake and come back. 

The area around the lake is covered with lush grasses that the herbivorous elephants depend on, said Venkatesh. But in the last few years, prosopis juliflora started taking over the corridor. The invasive species started replacing the native grass species, reducing the availability of preferred food sources for elephants.

“We successfully eradicated these species from 370 hectares of the corridor area. We are now sowing native grass species, and elephants are once again drawn to the area. The primary goal of this invasive removal initiative is to restore the natural forest eco-system with grasslands and improve habitat for wild animals,” said Venkatesh. 

However, eliminating alien species like prosopis juliflora and lantana camara is not easy, as they regrow even after they are removed or burnt. So, it has to be ensured that the model is sustainable and maintained in the subsequen years, he said. 

Alien species often replace native vegetation, altering or degrading natural habitats and reducing the availability of preferred food sources for wildlife, said Girigan Gopi of MS Swaminathan Research Foundation.

The displacement of native flora by invasive species may also lead to a decline in plant diversity, affecting the variety of food resources available for different animal species. It can even alter foraging patterns. Changes in vegetation composition can force animals to modify their foraging patterns or adapt to new food sources, which may not be as nutritionally rich, Gopi said. 

Preserving the natural balance of the ecosystems is essential to ensuring the availability of diverse and suitable food sources for the wild animals in the Western and Eastern Ghats. Conservation efforts are crucial to managing the impact of invasive plants on the food web and overall biodiversity as this poses a serious threat to the ecosystem and wildlife.

“In Tamil Nadu we have successfully reclaimed 493 hectares of pristine forest land from senna spectabilis, a toxic invasive weed that kills native vegetation. In a joint effort, Tamil Nadu Newsprint and Papers Limited has taken out around 21,178 tonnes of the weed from forest areas of Mudhumalai Tiger Reserve and Sathyamangalam Tiger Reserve and converted it to 6,000 tonnes of printing and writing paper,” said Sahu.

Nearly 15 grass and 5 legume species have been discovered growing in the area where Senna has been cleared. A previously unknown wild rice variety from Mudumalai has been discovered as well.  “We are absolutely delighted to see our forests coming alive. The area covered with toxic invasive weed about a year ago now has lush green grass providing food to gaurs, elephants, deer and other animals,” shared Sahu.