Explained: The tree fall incidents in Mumbai and why the BMC called for only planting native species
Over the past few days, Mumbai has witnessed a high number of tree fall incidents, which has led to suggestions from activists as well as the mayor of Mumbai that the Brihanmumbai Municipal Corporation should only plant species native to the city. The Indian Express explains the difference between native and non-native species, and whether planting more local tree varieties would reduce tree fall incidents in Mumbai.
Newsletter | Click for Today’s Best Explanations to your inbox
How many tree fall incidents has Mumbai witnessed in the past week?
No less than 2,364 branches and trees were damaged in the metropolis during the three days – from May 16 to 18 – when the extremely violent cyclone Tauktae swept the coast of Mumbai, with a wind speed reaching 114 km / hour. Of this total, 812 trees were uprooted, while 1,552 trees lost their branches. The total number of trees that fell over the three days was significantly higher than the total number of tree fall complaints that the BMC is dealing with during the four-month monsoon season. On average, BMC receives 600 tree fall complaints per month between June and September.
How many fallen trees were not native?
The BMC in its post-cyclone inspection found that 70 percent of the 812 trees were non-native species, including Gulmohar, rain tree, and royal palm, among others. In the process, BMC called on citizens and private organizations to plant only native tree species during planting campaigns.
What are the native or native tree species in Mumbai?
The BMC cautioned that native species should not be confused with old trees or trees that are widely present. For at least three decades, the government imported exotic species and new species of trees were planted across the city for beautification. For example, Gulmohar or Rain trees are widely distributed in Mumbai, but they are not native species.
By definition, a “native” plant lives, grows and reproduces naturally in a particular region. After studying the local agro-climatic conditions, including soil quality and wet weather, BMC prepared a list of 41 native trees that can be planted in Mumbai that are part of the Konkan belt trees. These are Wad, Pimpal, Umber, Kanchan, Kadamba, Gunj, Palas, Nim, Mahogany, Moh, Bahawa, Sag, Arjun, Ain, Kinjal, Sita Ashok, Undal, Nagkeshar, Champa, Shivan, Shirish, Karanj, Bakul, Bell , Taman, Hirda, Behda, Coconut, Amla, Khair, Tetu, Mango, Putranjiva, Wild almond, Bibba, Parijatak, Rita, Sandalwood, Phanas and Chafa.
Why do botanists and BMC find non-native tree species more prone to fall?
Mumbai’s native species can cope with the city’s excessive water / humidity conditions and can withstand heavy rains and wind. Experts said it’s not that non-native species won’t survive, but it will require more maintenance, attention and care and even after that the trees may not acclimatize. The roots of non-native trees are unable to cling to the ground, are fragile and give way in heavy rains or high winds. Botanists have warned that new species could also compete with native species for land, water and food. Foreign species can also carry diseases that can harm native species.
Is planting of foreign tree varieties the only reason Mumbai is seeing an increase in tree fall incidents?
Environmentalists and urban conservationists have said old trees and non-native species alone cannot be responsible for damage to the city’s green cover. It is not dead trees, but also healthy trees that are uprooted. Environmentalists have blamed the rapid materialisation of the increase in the number of uprooted trees.
A 2014 survey of 1965 “rain trees” by Vanashakti, found up to 4 to 5 feet of concrete, tar and other building material surrounding more than half of the base of the trees without much. of ground. Network of underground cables, the lack of percolation of water in the ground because of the concretization around the base of the trees weakens the trees causing trees to fall during heavy rains, especially on the trails. About 308 of the 812 trees that were uprooted were roadside, that is, on sidewalks and pathways.
According to Maharashtra (Urban Areas), Preservation and Prevention of Tree Act, 1975, a space of 1 meter must be left around tree trunks. The National Green Tribunal also ordered that there should be a space of one meter around tree trunks for better growth in order to preserve and protect the trees.
The BMC does not plant trees on the side of the road or on the trails. However, when constructing buildings and trails, roadhouse, underground pipeline, one meter space around trees should be left around tree bases / trunks.
What is the reason for the high number of branches falling in Mumbai?
Campaigners say this is happening due to unscientific tree pruning carried out by the BMC. According to the 2019 audit, there are over 1.75 lakh of roadside trees. The BMC claims that before the monsoon 60k-70k trees are pruned. However, the pruning exercise undertaken by the BMC is criticized for being “unscientific”. In 2019, a citizen-led tree audit in Colaba found that 17 of 100 trees studied on JD Somani Marg and Captain Prakash Pethe Marg are at risk of falling.
Experts said that the idea behind a pruning exercise is to keep the tree’s weight balanced, it should not tilt dangerously to one side. Mumbai Mayor Kishori Pednekar said she would write to the chief minister to amend the Tree Authority Act to allow BMC to cut more and more larger branches. However, experts have warned against arbitrary pruning of trees.
There is no set rule regarding the number of branches to cut or extend the canopy. Experts said it differs with each tree. If the winds hit a tree, it should go through it. Otherwise, air turbulence is created in a tree (large or small bush) which can pull it down. According to technical standards for arboriculture, no more than 20 to 30 percent of the tree canopy should be pruned in a year. However, random tree pruning continues in the city.
In accordance with the condition of submission of contractors appointed for the tree pruning exercise, a special condition has been included to have a horticulturist or arborist on board, but this condition is not mandatory.