New Delhi: As Delhi gets its first 10-year scientific roadmap to restore native biodiversity in its forests by systematically removing invasive tree species and exploring biological control methods, scientists have welcomed it as a “much-needed intervention”, while cautioning against unintended ecological consequences, particularly from introducing non-native organisms.The plan drawn up by Dehradun’s Forest Research Institute (FRI) identifies three major invasive species — prosopis juliflora (vilayati kikar), eucalyptus and leucaena leucocephala (subabul or river tamarind), which together account for nearly 40% of Delhi’s forest growing stock. The plan proposes their phased removal over 10 years, using techniques, such as the cut-rootstock method for prosopis and felling for the others. Only 20% of a forest patch will be treated annually to minimise disruption, followed by dense plantation of native species.In addition, the plan suggests exploring biological controls, including introducing seed-feeding beetles (algarobius spp.), fungi like fusarium oxysporum and alternaria alternata, and bacteria like pseudomonas fluorescens to weaken the invasive populations.However, scientists have urged caution, pointing out that even vilayati kikar was introduced by the British thinking it would do good to the local ecology, but ended up hampering it.Faiyaz Khudsar, scientist-in-charge of DDA’s Biodiversity Parks Programme, warned that introducing new species could repeat past ecological mistakes, and suggested thorough research in closed systems. “Biological control of such invasive species is not easy. We don’t know the overall impact on the ecosystem or how these organisms will behave,” he said.Drawing parallels with invasive fish like tilapia and Thai mangur, he added, “Any introduction needs careful investigation, preferably in a closed system, because we’ve already seen how species introduced with good intentions, like prosopis itself or water hyacinth, became major problems.”Khudsar also noted that while prosopis is invasive, it has over time created a “surrogate ecosystem” in parts of Delhi, helping stabilise soil and microclimate. “Pulling it out entirely must be done carefully,” he said.Echoing concerns over biocontrol, Prof C R Babu, a veteran ecologist and architect of Delhi’s biodiversity parks, strongly cautioned against introducing seed predators. “Any biological control will be dangerous. These organisms may not restrict themselves to prosopis but also attack native species, affecting their regeneration,” he said.Instead, Babu advocated proven ecological restoration methods, such as the “canopy opening technique”. He explained, “Create small ‘canopy gaps’ to allow sunlight, plant fast-growing native species and gradually suppress prosopis. This has worked effectively in places like Kamla Nehru Ridge.” He also supported the removal of subabul and eucalyptus, noting they are less ecologically integrated.Sohail Madan, ecologist and director at WildTales Foundation, described the plan as a “vital, science-led boost” for Delhi’s forests, but stressed the need for rigorous testing. “Biocontrols like agarobius beetles demand strict pilots — past rushed introductions elsewhere have damaged native flora,” he said.Madan emphasised that Delhi could become a model for urban rewilding if the implementation is cautious. “These North American agents risk non-target impacts in our biodiversity hotspots. Integrating them with mechanical removal and community monitoring will be key to safeguarding native habitats,” he added.The experts also flagged regulatory hurdles, which have been casually suggested in the workplan. Tree removal in Delhi requires permissions under existing law like Delhi Preservation of Trees Act, and work in Ridge areas needs Supreme Court clearance, factors that could delay implementation of the plan.
