Pradip Krishen is the author-photographer of a celebrated new book Trees of Delhi – A Field Guide. He also directed the critically-acclaimed films Massey Sahib, In Which Annie Gives It Those Ones and Electric Moon. He and his wife Arundhati Roy lives in New Delhi.

[This is the finale of the three-part interview series he gave to Mayank Austen Soofi. The second dealt with the history of Delhi's tree scene.]

Welcome back, Mr. Krishen. According to you, what is the biggest threat confronting the tree flora of Delhi today?

A difficult choice! The mindset of expansion and redevelopment is deadly because it doesn’t ask what the desirable outcome should be, it tries to feed insatiable and unsustainable demand. Such planning is deadly and will always be inimical to trees and open spaces.

The 2010 Delhi Commonwealth Games, as I’ve said, could well turn out to be a major cause of destruction. But even more deadly, to my mind, is the lack of understanding of the relationship between trees and the ecology of Delhi. We are in grave danger of miscalculating the extent to which trees will survive when Delhi’s ecological parameters are stretched. What will happen when our groundwater plummets by another 20 or 30 metres? We face the horrible prospect that there will be no water left to spare for luxuries like trees.

Mr. Krishen, you are involved in promoting what is termed "native plant gardens" – planting trees that best adapts to the soil and climate of the land concerned. How successful have your efforts been?

I need to correct your definition slightly. I’m planting trees and shrubs (and herbs and grasses) that already belong to the site in question. That’s how they’re "native". In another context, it might be called "eco-restoration", and the rationale is terribly simple: if you use plants that are already adapted through millions of years of evolution to local conditions, then in theory, once these plants are established, they should need nothing else, no water or nutrients or artificial help in any way to survive in that environment. In actual fact, it’s a little more complicated, because there’s competition from other, more aggressive plants, usually exotics, and there’s pressures related to human interference. But it’s a good philosophy to begin with, and then you have to adapt to the contingencies.