Mapping Chennai’s canopy by Hema Vijay

From The Hindu, April 12th 2013

T.T.K. Road, once an avenue of banyan trees, today has none. In Thiru-Vi-Ka Park, seven huge Trincomalee Wood trees and a large Barringtonia tree got the axe for the Metro Rail project. In St George’s Cathedral, a large and very rare Button tree was cut to make way for an exhibit centre.

We plant trees randomly but worse, we cut trees randomly, with not a thought for maintaining urban green spaces, or preserving tree species. As a result, much of Chennai’s tree wealth has been wiped out, with rare and irreplaceable trees routinely cut to make way for roads, houses or bus-stops.

A lot of this happens because botanists are not consulted before trees are cut. “Some trees can be transplanted; others can be preserved by designing infrastructure or routes around them,” says Dr. R. Pauline Deborah, professor of plant biology at Women's Christian College. The average person is not even aware of which tree is rare or really old.

Now, that could change. Over the last four years, Deborah has trudged through the city to collect images and data on Chennai’s trees for her thesis on ‘Tree Diversity in Urban Landscaping with Special Reference to Chennai’. The massive and comprehensive databank can now be used by policy-makers to preserve the city’s irreplaceable tree wealth and develop Chennai along sustainable lines.

“A map on tree cover can be used to guide planned development in the city, be it residential, commercial, educational or governmental. The Indian Constitution already stipulates this but there is no compliance,” says Dr. Abdul Razak, Professor and HoD at the School of Architecture and Planning, Anna University.

Deborah’s research includes Chennai’s tree diversity and how it has changed across the years, rare trees and their locations, heritage trees and their locations, tree hotspots, spatial distribution maps of trees, ratio of exotic species vs. native species, and much more. For instance, she found that the ratio of exotic to native trees in Chennai is 70:30, an ecologically disastrous scenario. “Exotics are suitable for a few home gardens, parks, institutions or botanical gardens. They are highly unfit for planting as avenue trees since they can easily topple during monsoons and cause fatal accidents and property damage. Moreover, exotic species can alter the water table or soil pH. Some of them can even turn invasive like the Mesquite, Muntingia and Custard Apple, posing a threat to native vegetation,” says the professor.

Architecture students are routinely asked to map trees, water bodies and other natural features of a site and come up with building designs that preserve these. During professional practice, though, this aspect is often overlooked. “To ensure compliance, it must be legalised, with the local government monitoring the construction,” says Razak.

At the very least, it requires widespread awareness creation, which is where tree data becomes invaluable. “User friendly, web-based, open-source collaborative technology that improves information sharing, communicates the value of urban forests, and engages communities in creating greener urban environments is an imperative need,” says Shobha Menon, founder trustee, Nizhal, which has mapped trees in areas such as Valmiki Nagar and Gandhi Nagar.

Deborah’s research finds that 54 tree species in Chennai are restricted to just 3 per cent of the city, and she warns, “This includes some very rare trees that exist as single trees or in small populations of less than a dozen, and they are at risk of being totally wiped out from the city if cut. For example, Gustavia Augusta Trees or Tree Lotus have beautiful flowers resembling a small lotus and are found only inside the Theosophical Society. There are only 34 heritage trees like the Baobab left in Madras Medical College. Each has a girth of about 10 m and is more than 150 years old; they need protection.”

Rare tree hotspots in Chennai include the Theosophical Society, Agri-Horticultural Society, Guindy Reserve Forest, IIT, Raj Bhavan, Women’s Christian College, Madras Christian College, Nageswara Rao Park, Anna University, YMCA Nandanam, Pachiappa’s College and Presidency College.

The pity is that, thus far, tree mapping and city planning have remained largely isolated from one another. Perhaps the new databank could change this.