Need to plant more trees

THEY KEEP CITIES COOL

During the hot summer day, the shade of a tree is a welcome relief. However, if there are mini forests, it can create profound cooling effect.

According to a study published on March 25, 2019 by National Academy of Sciences, USA, trees play a vital role in keeping our cities cool. Carly Ziter and Monica Turner, professors from the University of Wisconsin-Madison are the authors of the proceeding.

Climate change makes extreme heat events during summer and the city planners are working to find solutions. Heat waves increase energy demand, which adds to the cost and can also have big impact on human health.

Authors say that roads, sidewalks and buildings absorb heat from sun during the day and release in the atmosphere during the night.

However, the presence of the trees cannot only provide shade to the surfaces from sun rays, but can also transpire and release water in the atmosphere through leave surfaces and bring down the temperature.

The study has further found that the maximum benefit from cooling services can be found if the canopy covers of the trees are more than 40%. The right amount of tree cover can lower the summer daytime temperature by 3 to 5 degree centigrade.

The study has also confirmed that the city areas with lesser vegetation are warmer than rural areas around them. Planting of one tree can have little impact, but it is suggested to plant more trees to have appreciable impact.

Often, city corporation planners have misplaced priorities and they tend to cover the earth with impervious tiles/concretes. Zilter, lead author of the study, says: “The trees we plant now or the area we pave now are going to be determining the temperature of our cities in next few decades.”

Let us understand the situation in our context, in the light of the above study. The Forest Department and city corporations undertake several tree planting programmes these days.

Also the natural tree groves left in some patches within city limits serve the same purpose. In addition to fresh planting, these patches are to be preserved and it has to be ensured that the trees are not cleared and the area is not diverted for any urban project.

We need to draw a policy of keeping 40% area for tree planting in any city/town. Often, we acquire land for any infrastructure development projects for decongestion of traffic and also for providing basic amenities like school, health, water supply etc for the growing urban population. Old standing trees are sacrificed for expansion of infrastructures.  

It is the older trees which provide big foliage, more shade and large leaf areas. More leaf areas mean more transfer of water vapour to the atmosphere through transpiration and hence greater cooling.

Thus, the cooling effect provided by older trees is far too higher than the young ones. Whenever we chop off old trees and even if we plant ten times the number, there is bound to be an increase in day time temperature of the locality.

In a city like Bengaluru, the BBMP is engaged in management of trees in its limit. The civic body has a forest wing which discharges this responsibility.

Presently, trees are being removed for Metro rail works, widening of roads, and construction of flyovers. Many trees may have to be sacrificed in future for projects like elevated corridors, expansion of Metro rails in other areas etc.

While these projects are necessary, it is also more important to take up planting in city limits. We need to have foresight and take up plantations in city at least a decade ahead of removing old trees.

Principally, we should acquire land exclusively for plantations. Whenever we acquire land for widening of the road, we must make provision for at least one row of planting on either side.  

Overhead electric transmission and telephone lines are also hazard for growing big and shady trees in the city. Often, the branches grow and interfere with these lines. During annual maintenance the branches are chopped off. Sometimes, even the leading shoot is cut away and tree grows only sideways. This is clear example of lack of coordination between BBMP, Bengaluru Electricity Supply Company (BESCOM) and BSNL.

As far as possible, Forest Department should not take up planting under the overhead lines and on the other hand the agencies should invariably bury the lines underground.

Roots of the trees are also damaged while carrying out maintenance works of sewer lines, underground pipes supplying water and underground cables. All we need here is to ensure that the tap roots are not damaged while side roots can be damaged.

The forest wing of BBMP should carefully choose species, which are not shallow rooted. Trees with shallow roots meet with the casualty during heavy wind.

Side roots

In the process of producing tall seedlings, often tap roots are damaged. When such seedlings are planted, they grow with the support of the side roots and are vulnerable for fall during heavy winds. They can cause damage to life and property.

It is therefore recommended to use relatively smaller seedlings where tap roots are intact, trees will then stand more firm on the ground.

Footpaths are often covered with concrete / tiles, leaving very little space for existing trees to absorb rain water. Once the tree falls, there is no space to plant another.

It is recommended to leave a linear strip of at least 3 feet width for growing trees on either side of roads.  Recently, BBMP removed all big trees along Church Street and covered the footpath with tiles, leaving very small holes for planting dwarf palm trees.

The study of Wisconsin University has clearly brought out that the plant with small foliage is no replacement for big trees. The BBMP must undertake several course corrections as explained above.

(The writer is former Principal Chief Conservator of Forests, Karnataka)

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