Why did so many trees fall in Delhi? Experts have a theory

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Poor root growth due to concretisation could be a factor that caused trees to keel over, said ecologist C R Babu. “If there is proper root growth that anchors trees to soil, they won’t fall over easily. Most trees have ‘feeder roots’ that are in the upper layers of the soil. These roots take nutrients and moisture, and have symbiotic fungi in and around them. But these roots cannot survive under concrete, since they need oxygen. If the space around trees is covered with concrete, there will be no life beneath the concrete,” he said. “The canopies of the trees are also not managed properly. If the top is heavy and the root is poorly developed, how can the tree sustain the wind? Different species have different tensile strength,” he added.

An NGT order from 2013 states that concrete within a 1 metre radius of trees is to be removed. A notice was issued in 2019 by the forest department, informing all departments and civic agencies that concretisation of trees damages them and is an offence under the Delhi Preservation of Trees Act, 1994. The notice also asks the agencies to manually deconcretise trees.

Many of the incidents were recorded in the Central, New Delhi and North districts of the capital.

“Leaving 1 metre around the trees is not enough to have sustainable growth of avenue trees. They need to have good feeder roots that can spread to take in nutrients. But there are limitations considering the width of the pavements,” Prof Babu said.

Navneet Srivastava, DCF, West Division, said, “If the tree is concretised from all sides, there is a greater chance that it will fall. It could definitely be a factor in huge trees falling.”

Faiyaz Khudsar, scientist in charge of the Yamuna Biodiversity Park and the Biodiversity Parks Programme, said, “On the central verge of the road, there are trees like sheesham and silk cotton grown in small places and then surrounded by concrete. How will the roots spread? In the long-run, roots spread laterally. Winds put pressure on big canopies, which means that the canopies are big, but the root is unable to withstand the pressure.”

Some of the avenue trees in the Lutyens Delhi area began to be planted in the 1930s, said environmentalist Pradip Krishen. Neem trees have thick canopies, he said: “One factor for trees falling could be that, as our water table has dropped, the trees with tap roots are no longer in touch with water. Another factor could be the cementing of sidewalks. But without doing a proper study, we’re just guessing.”

“If we plant tree species that are native to Delhi and ensure diversity while planting avenue trees, survival and sustainability become easier. Age is also a factor. So, where trees are getting older, you start planting new trees of different species,” Khudsar said. Other parts of the city also recorded instances of trees or branches falling. The offices of the MCD received 155 complaints between 9 pm Monday and 3 pm Tuesday, from areas including Daryaganj, Civil Lines, Jama Masjid and Mayur Vihar.