New Delhi, July 21 -- Two days ago, I took in a deep breath and felt as if I was aboard a time machine. I could smell the rich, spicy, fragrance of the neem tree. Not the flowers but the fruit, the Neembori, many of which had fallen to the ground. This was a fragrance I hadn't taken in for several years. The reason, once I looked around, seemed obvious. I was surrounded by at least 18 neem trees, and their fruit were hitting the soil -- half smashed, half absorbed into the damp mud, turning it into a perfumed plot. In most cities, except for orchards or trees along roads, it is becoming harder to see groups of one species. Of course, there's less space, but the aesthetic is also fading. Planting a single species near each other can enable i...