Drive to save Delhi’s central ridge from invasive tree species

NEW DELHI: To weed out the invasive vilayati kikar (prosopis juliflora) from a 20 hectare area of the Central Ridge, the Delhi forest and wildlife department will be carrying out pruning of these trees for a period of around three years and simultaneously growing native Aravalli species next to them as part of an eco-restoration project launched by environment minister Gopal Rai on April 27.

Forest officials said while a major chunk of the invasive tree species has been pruned in the pilot project area, adjacent to Vande Mataram Marg, the plantation work is set to begin next month, when the monsoon hits the Capital.

HT extensively reported on the problems arising out of kikar trees in the Delhi’s ridge in 2017. The kikar ( Prosopis juliflora) was brought to the city from Mexico by the British more than a century ago.

The exotic plant became invasive and wiped out most of the native plants and along with it the animals, which once used to roam in the ridges. It also wreaked havoc on the city’s groundwater levels.

In his assessment at the time, author and naturalist Pradip Krishen advocated uprooting of the kikar to allow other plant species to survive.

“The kikar’s roots secrete a kind of toxin ( an alkaloid) which inhibits the growth of other plants. It was because of this that most native trees vanished. Only a few plants such as the Kanju can withstand this toxin but most plants can’t. Just planting a native tree and allowing sunlight doesn’t help. It has to be uprooted from at least 30 inches deep in the ground,” Krishen, author of the book, Trees of Delhi, then said.

A senior forest official said that while a 10 hectare area was initially chosen for the pilot project, it was widened to 20 hectares now, and depending on how the project proceeds, foresters will be able to make an informed decision on whether the invasive tree species can be naturally killed or removed.

In total, 423 hectares of the 864 hectare Central Ridge is to be ecologically restored in the long run, the official added.

“We will keep pruning these trees at regular intervals to create enough room for sunlight to penetrate through to the ground, where native saplings are being planted. Once these native saplings grow to a good height, over the next two to three years, they will be able to compete with the vilayati kikar and eventually, there will be more native species than vilayati kikar, which currently dominates the Ridge,” a forest official said on condition of anonymity.

While announcing the project in April, Rai had said that a list of native trees had been prepared for eradicating vilayati kikar, and the longterm plan was to remove the invasive species from around 7,500 hectares of forest land across Delhi.

“The exercise of removing the invasive species will be done by the “canopy lifting (tree pruning)” method. Under this project, the Central Ridge would be freed from the vilayati kikar and a “cut root stock” method will also be used to prevent the expansion of this exotic species. At the same time, native species in large numbers will be planted in the area,” he said at the time.

In the cut root stock method, the root of the plant is cut three inches below the ground with minimum disturbance of the soil. The bush is then lifted up and kept upside down to prevent it from gaining ground again, forest officials said.

The plan to carry out an overall ecological restoration of the Ridge was devised in 2018, but cabinet approval for the project came only in February 2021.

The forest department was unable to start work last year, largely owing to differences in opinion among the expert members a technical committee constituted for the project.

This committee was eventually scrapped, with the project now being executed by the forest and wildlife department, officials said.

They said the native species identified for plantation include hingot, banyan, bahera, cabbage, Chamrod, pilkhan, amaltas, mulberry, palash, native acacia, khair, bitter gourd, gular and harsingar, among others.

Along with these, shrubs such as ghatbod, curry leaves, shatavari, karonda, ashwagandha, and jharbera will also be planted.

“We will use the pilot project to determine which native species are able to flourish alongside the vilayati kikar,” the forest official quoted above said.

The other components of the ecological restoration plan include incorporating parks in the vicinity to create a large green grid, with butterfly and bird safaris also planned for the future.