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Delhi: Indigenous vines to be used to kill ‘invasive’ tree species

Scientists have identified seven species of plants, mostly vines, that they claim are ‘killing and replacing’ the ‘vilayati kikar’

delhi Updated: Mar 11, 2018 23:42 IST
Joydeep Thakur
The population of kikar or Prosopis juliflora has gone out of control destroying the biodiversity in Delhi’s ridges.
The population of kikar or Prosopis juliflora has gone out of control destroying the biodiversity in Delhi’s ridges.(Ravi Choudhary/HT PHOTO)

“Enemy’s enemy is a friend”. And now Delhi University scientists are taking up this age-old proverb in their fight against ‘vilayti kikar’ — an alien invasive species of tree that has played havoc with the city’s biodiversity for long.

The scientists have identified at least seven species of plants, mostly vines that they claim are killing and replacing the kikar. It is a kind of biological control of the kikar, which the researchers have stumbled upon.

“Kikar, like any other plant, needs sunlight for photosynthesis — a process through which they manufacture food. The sunlight is needed to produce glucose from CO2 and water. These climbers, once they reach the top of the kikar, gradually engulf the entire canopy. As a result the kikar doesn’t get sunshine and can’t perform photosynthesis. Eventually they die,” said CR Babu, who heads the biodiversity parks project of Centre for Environmental Management of Degraded Ecosystems at DU.

The kikar or Prosopis juliflora was brought to Delhi 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. With its deep roots, it had also wreaked havoc on city’s groundwater.

“We have identified at least seven species of vines that are killing the vilayti kikar along the Kamla Nehru Ridge. At least 20-30 kikar trees in the northern ridge have already died and many are in the process of drying up, as the sunshine has been cut off by the climbers. You can tell that they are dying just by looking at them. They don’t look healthy anymore,” said AK Singh, scientist in-charge of the Kamla Nehru Ridge.

While two of them are exotic species, including bougainvillea and rubber vine, five are native to India. Most of the native species have high medicinal value. The geloi (Tinospora cordifolia) is used to treat liver diseases, makora (Jackal jujube) is good to treat stomach ache and Asian bushbeech (Gmelina asiatica) is used as a blood purifier.

Scientists said the climbers can attack any tree, as they need a support to grow. As the kikar is the most dominant species in the northern ridge and can be found everywhere, they have come under attack.

“The woody stem of the rubber vine is so strong that it literally strangles the plant. We have seen such strangulation marks even on a banyan tree in the ridge,” said Faiyaz Ahmed Khudsar, scientist in-charge of the Yamuna Biodiversity Park.

The kikar’s leaf contains toxins, which when falls on the ground, inhibits the growth of other plants. That is why several native plants were almost wiped away. But these toxins hardly have any effect on these climbers.

Experts said that unlike the kikar, which is an alien invasive species and had gone out of control destroying the local biodiversity, these native species would do no harm to Delhi and the ridge.

“The kikar was harmful because it came from outside and was gradually destroying the local biodiversity. But these plants are native to India and are a part of the local community. Hence, they can’t be harmful for the ecology,” said Khudsar.

The kikar’s deep roots absorb water, leaving the ground almost dry. As a result other native plants used to dry. But while some of these climbers have tuberous roots which can store water for the growing plant, others like the geloi can absorb moisture from the air with their hanging roots.

Over the past few years, the Delhi government had been trying hard to find out ways to eliminate the kikar. While the government had allocated Rs 50 lakh in its budget in 2017, the forest department had approached the Forest Research Institute to finalise a plan to do away with the menacing species.

Hindustan Times had earlier reported that scientists were trying to find out ways to replace the kikar with other plants. They had to trim the thick canopy of the kikar so that sunlight could reach the forest floor and allow native plants to grow. But later they stumbled upon these seven species of plants that could eventually help in eliminating the kikar.

“Plants such as the geloi grow naturally and abundantly. There is no need to plant their saplings. We just ensure that they don’t attack other plants such the banyan. If we see any indigenous plant like the banyan being attacked we remove the climber to save the tree. When it comes to the kikar, we just allow the climbers to engulf it,” said Harmeek Singh, supervisor of the Kamla Nehru Ridge.

“We cannot just cut down the kikar as it is prohibited. But now that we have identified some native species, which can help us in replacing the kikar, we are planning to take this model forward in other parts of Delhi. You can say this is some kind of biological control for the kikar,” said Babu.