That green symbolises hope, happiness and new life is ancient knowledge. But how much could the presence of trees in our contemporary neighbourhood improve the health of residents?
A paper published in Scientific Reports on July 9 quantified the relationship between trees and health. It found that having 10 more trees in a city block, on an average, improves health perception in ways comparable to an increase in annual personal income of $10,000 and moving to a neighbourhood with $10,000 higher median income or being seven years younger.
The researchers conducted an online health survey of 31,109 residents of Toronto, Canada, and combined the findings with high-resolution satellite imagery and tree data. They also found that having 11 more trees in a city block, on an average, decreases cardio-metabolic conditions such as heart disease, stroke, diabetes, obesity, etc., in ways comparable to being 1.4 years younger.
Trees sustain a city like nothing else can. They deal with atmospheric pollution, a dire problem in Delhi that houses 8.8 million vehicles and where respiratory diseases among citizens are most common. In fact, a single tree releases enough oxygen to sustain two people, according to a study by Trust for Public Land, Sacramento, USA.
Hundred mature trees can reduce runoff caused by rainfall by up to 1,00,000 gallons, says the US Department of Agriculture. In Delhi, our government agencies spend Rs 500 crore annually on controlling waterlogging and floods.Yet, one downpour and the capital’s streets morph into streams.
Trees also replenish groundwater, a boon in a city that has already been sucked dry. Besides, the USDA Forest Service has found that the cooling effect of a healthy tree is equivalent to 10 standard domestic air-conditioners operating 20 hours a day. Those living close Delhi ridge or city forests will vouch for that.
Yet, trees remain the worst casualty in Delhi’s urbanisation. More than one lakh trees were cut between 2006 and 2014 to make way for the metro, roads, flyovers and government buildings, the Delhi high court was informed in April this year. Permission to fell more is waiting for approval.
With 20% forest cover, Delhi is one of the greenest cities in India. But the green cover is determined from satellite imagery and does not reveal how much of it is actually contributed by thickets of thorny shrubs. It does not tell us the health of the trees either.
The Delhi Preservation of Trees Act, notified in 1994, mandated a tree count but the first city-wide census is yet to be conducted. In 2005-06, the New Delhi Municipal Council did count the roadside trees in the VIP zone, studied their health and also got itself a tree ambulance. It is the only such facility in Delhi.
Having long waited for the government, residents of Sarvodaya Enclave were the first to conduct a tree census in 2011. Gulmohar Park, Vasant Vihar, RPS Colony and G K-4 followed. More than numbers, the health of the trees are the priority of these residents.
Harming a tree attracts jail term of up to one year or a fine of up to Rs 1,000 or both. It is mandatory to leave 6x6 feet open space around each tree while paving footpaths. But most city trees are sealed with cement or impaled, lopped and hammered. At least 200 full-grown trees anyway die every year because of storms, water scarcity, excessive concretisation, disease and old age.
Our plantation drives have mostly favoured non-native varieties mostly because of their pretty looks. But experts point out that trees native to an area adapt to its soil and ecology over hundreds of years. Such plants take care of themselves without draining resources such as groundwater. Exotics, on the other hand, are resource-hungry and often crowd out native species.
In any case, it is impossible to compensate the killing of an ancient tree by planting a few saplings. With its river and air turning noxious, the last thing Delhi can afford today is to risk its remaining trees and the green capital status. More than vanity, it is a question of well being if not plain survival.