There is a raging debate among naturalists about the desirability of cultivating exotic plant species and there are no easy answers. My own view is that we should try our best to avoid introducing any new species into an existing ecosystem but there is no need to get worked into a froth if a species has naturalised over a substantial period of time. Yes, there are places where exotic species have become very invasive at the cost of the local varieties and there may be a case for culling them – but such a discussion is beyond the scope of this article. Instead, we are going to focus on the use of exotic and native species in the context of what is appropriate landscape architecture in a predominantly hot country like India.
Improving Comfort Levels
Trees are often the first line of defence when it comes to passive cooling of a bungalow or other low-rise structure. They provide shade which prevents the build-up of heat not only on the ground but also on the walls of the building. Shade on the ground means the breeze coming in through your window is cooler and shade on the walls means less heat gets transferred indoors. Aside from shading, trees also cool by transpiration to the extent that they can, if properly located, reduce ambient temperatures by as much as 5° compared to the surroundings.
So what kind of trees should we plant, and where?
While the finer details vary across different parts of the country, broadly it is safe to say that the hottest sides are the South and West so, if you can concentrate on protecting these directions with dense evergreens, you’re good to go. On the East, you might want to have high-branching trees that won’t block your early morning sun and on the North – depending on whether you get direct sunlight penetration or not – you could grow colourful, possibly deciduous trees. You have to be careful during plantation that you leave enough distance between the tree and your foundation because many of the large trees have strong spreading roots.
Trees, even in urban areas (albeit to a lesser extent), are part of an ecosystem and need to treated at as such. If they are native, they will invariably be well integrated into that ecosystem along with the local fauna like the birds and butterflies. An introduced plant is unlikely to be so well assimilated and may therefore not contribute in a positive way. There are plants that have been naturalised over a long period of time but I’m referring to those that have been introduced because they are ornamental or because they grow rapidly. Usually the ornamental ones are fragile and drop their branches on your head at the beginning of the monsoon and the fast-growing varieties with their short life-spans often sap the soil so severely that nothing else grows there for years after they’re gone.
Usage of Water
This is a very important factor to take into consideration especially if you’re thinking of sustainable landscaping. Many ornamental trees and bushes are extremely high-maintenance and don’t even get me started on lawns. They may look very pleasing to the eye but, with few exceptions, they guzzle frightening amounts of water and are often heavily sprayed with chemical pesticides — which naturally leech into the groundwater.
Here, a very important argument for using native species is that they will, by default, survive with the naturally available moisture and precipitation. Of course they may need some amount of watering when they are saplings as also during the hot summer months but, in general, their water requirements are a small when compared to exotic ornamentals.