Delhi govt plans to weed out invasive plants in Ridge

Jan 27, 2023 02:01 AM IST

The project will commence at atentative cost of ₹1.09 crore. Once cleared, the weeds and cleared waste will be dumped in parts of the Asola Bhatti Wildlife Sanctuary

The Capital’s forest and wildlife department has floated a tender to get rid of both vilayati kikar (Prosopis juliflora) and Lantana camara-- two extremely invasive species--from a 132-hectare area in the southern ridge, officials said Thursday.

Vilayati kikar tree at the Northern Ridge in New Delhi, India. (HT Archive)
Vilayati kikar tree at the Northern Ridge in New Delhi, India. (HT Archive)

The department had begun a pilot project last year to remove vilayati kikar from a 20-hectare area of Delhi’s central ridge, which is still underway.

According to the tender document, which HT has seen, the project will commence at atentative cost of 1.09 crore. Once cleared, the weeds and cleared waste will be dumped in parts of the Asola Bhatti Wildlife Sanctuary, the tender added.

“...the task includes clearing Lantana camara and Prosopis juliflora (from the) jungle, including uprooting of rank vegetation, grass, brushwood (undergrowth), trees and saplings of girth up to 30cm measured at a height of 1m above the ground level and removal of rubbish up to a distance of 50m outside the periphery of the area cleared,” the tender said.

Vilayati kikar is an invasive Mexican tree species, introduced in Delhi by the British in the 1930s, which has systemically taken over the Delhi ridge, making it difficult for other native species to grow. The roots can grow to a depth of over 50 metres, depleting groundwater, while its leaves contain toxic chemicals which prevent them from microbial degradation.

Lantana camara is a weed with south and central American origins. It has over 600 varieties. The weed is considered among the top 10 worst invasive species by the International Union for Conservation of Nature (IUCN). Experts say it impacts the growth and spread of native shrubs and plants as well as the ground-level ecosystem.

Officials say they will use the cut-rootstock method to clear both species, and target only smaller plants and not fully grown trees. The cut-rootstock method involves making a small, diagonal cut on the plant under the soil to remove its roots 5-8cm below the surface, without disturbing the soil. This method ensures the roots of the weed or plant are cut without disturbing the seeds.

The forest department has been using the same technique from June 2022 to clear 20 hectares in the central ridge of both vilayati kikar Lantana camara.

“This method has proved useful already and is now being replicated in the southern ridge. Fully grown trees will not be impacted, but the aim is to prevent further growth of new vilayati kikar and Lantana,” said a forest official aware of the matter.

CR Babu, head of the Centre for Environmental Management of Degraded Ecosystems (CEMDE), who discovered this technique, said other methods such as the use of herbicides, pests or burning have failed. “If one simply removes the plant, the roots stay and it regrows quickly. If the roots are also uprooted, hundreds of dormant seeds lying underneath the surface start to germinate and the growth is denser than before. Countries have also tried to use insects to kill these plants naturally, but the insects can then damage other plants too, and herbicides pose the same risk,” he said, adding once tackled efficiently, other native ground species can begin to grow naturally.

Once the cut plants are dumped in a fresh pit and covered with soil, Babu said they will not regrow.

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