The deception of ‘green’ when alien species invade

CHENNAI: Forest lands in the State, especially in Western Ghats, are turning into ‘Green Deserts’ as the invasive alien plant species pose a severe threat to the ecological balance of Tamil Nadu’s forest areas.

Despite the State Forest Department’s preparation of a policy for restoration of forest areas, the work to remove such invasive alien species is yet to commence.

A forest department official said that alien plants were introduced to the State advertently and inadvertently. “Species such as mucuna bracteata (commonly known as mucuna) was introduced as cover crop in the rubber plantations of Kanniyakumari near Western Ghats to increase nitrogen content of the soil. Similarly, Lantana Camara (unni mullu) was introduced as an ornamental plant. Wattles were also introduced in the State purposefully,” the official pointed out.

Apart from mucuna and lantana, acacia wattles (savukku), eucalyptus, prosopis juliflora (veli kaathaan) and others have occupied a considerable amount of forest areas. The official added that removing the alien species like prosopis juliflora and lantana camara is difficult as they regrow even after they’re burnt.

Explaining the impact of such invasive alien species, the official said that they’d spread rapidly and prevent other native species from surviving in the forest areas. “Mucuna will cover the land like a blanket; even sunlight would not penetrate. This would affect the biodiversity of the forest. For the layman, the forest covered with alien species would look greener. But the forest areas are becoming green deserts rendering the land unusable for other purposes,” lamented the forester.

The State government had constituted a committee in November 2021 to prepare a policy for the eco-restoration of forest areas that were infested with invasive species. The committee released TN Policy On Invasive Plants and Ecological Restoration (TN PIPER) a few months ago.

During the process of framing it, the committee found out that over 3.18 lakh hectares of forest land in the State were invaded by 7 most common invasive alien species. Lantana camara is the most widespread that covers over 1.66 lakh hectares of the forest.

For example, an assessment conducted in 2020 revealed that 262 sq km (69%) of montane grasslands in the Palani Hills and 180 sq km (58%) of montane grasslands in The Nilgiris have been lost due to exotic tree invasion and agricultural expansion.

V Naganathan, APCCF (Wildlife), said that the forest department could only survey the extent of forest land affected by invasive species.

“We cannot survey such species in the lands owned by other departments or by private persons,” he said.

He added that the government was working on launching a massive drive against the invasive species, but it required huge funding for removal, and restore the area by planting native species. For some species like prosopis juliflora, the forest department can monetise after felling plants.

“We can use the money generated again for clearing more areas. However, we cannot monetise on plants such as lantana camara. As the funding is huge, we need a corporate social responsibility fund, community help and assistance from NGOs,” he explained.

Naganathan explained that vegetables like tomatoes, radishes and others were also alien species, but they did not invade nearby areas and their growth could be controlled.

As per the TN PIPER policy, the forest department has constituted district level committees to oversee removal of invasive species and restoration of infected lands. It has also recommended the development of Invasives Removal and Restoration Protocol (IRRP) for non-forest areas with the concerned departments that deal with land.

The policy urges the government to make invasive species management an integral part of human wildlife conflict mitigation schemes as they colonise wildlife habitats and displace animals. “Invasive alien plant species, especially in the upper catchments of river basins, can have substantial hydrological impact. So, river rejuvenation and watershed development programmes need to focus on to its’ removal and ecological restoration,” the policy said.