So many of the world's best books happen on foot; far more writers are walking animals than sedentary ones, returning to the desk to set down an account of where their travels took them.
Very rarely, the walking doesn't just enable the writing: it shapes the books themselves. The books that come out of these voyages of slow discovery tend to be classics - John James Audubon's The Birds of America, Laurie Lee's As I Walked Out One Midsummer Morning, anything by Charles Darwin, the works of E P Gee and M Krishnan, and now Pradip Krishen's monumental, engaging Trees series.
Some years ago, a friend gave me Charles Darwin's key works, and his journals. The overlap between the two brought the man himself and his endless delight in discovery alive. At almost exactly this season - the beginning of March - Darwin noted his first walk in some days after being on board ship for a while: "The day has passed delightfully: delight is however a weak term for such transports of pleasure: I have been wandering by myself in a Brazilian forest."
The next day, March 1, he writes again - a short diary entry, you can sense his eagerness to get back to his explorations the next morning: "I can only add raptures to the former raptures." He ignores slovenly and thieving hotel-keepers, the occasional intestinal inconvenience, the other little impediments to travel, savouring the visual and tactile pleasures of discovery. Darwin spent his life walking, collecting and then settling down from the active tramping to the quieter business of coming to certain theories about men and other apes.
Pradip Krishen, like Darwin and a score of other naturalists, has built a life through the simple business of walking. Trees of Delhi, his first handbook, changed the lives of many of his readers. We began by using Mr Krishen's guide as a simple way of recognising the trees in our own neighbourhoods. Some of us ventured further out, and further still, until we were claiming parts of Delhi we'd forgotten about, or never visited.
As the trees of the city became visible, the city became less and less alien. And Mr Krishen asked interesting questions: how did the nostalgic yearning of the colonisers for stately avenue trees change the landscape, what kind of tree was "natural" to Delhi's climate? And why was nature held at such a safe remove in cities - something we went to visit, as though it was an elderly and ailing relative?
One day, exploring Vasant Kunj's urban forests, I looked out, sighting along a line of keekar trees; we had grown up thinking of keekar as ugly, thorny, spiky, nothing like deodars, mango trees, neem trees or other "real" trees. But I had been reading Mr Krishen's book, and something shifted in my field of vision: the sudden fragile grace of a keekar's thin, floating limbs was revealed. Once glimpsed, that beauty has been permanently acknowledged by something in my brain beyond my conscious control, and it cannot be unseen.
"I like trees. Especially wild ones." Mr Krishen's introduction to Jungle Trees of Central India: A Field Guide for Tree Spotters (Penguin) begins with that bold declaration of love. This book was 20 years or more in the making, if technically a few years in the compiling. Two decades was how long it took Mr Krishen to learn to identify trees, and to invent his present line of work as a practising Ent, like the friendly, solemn guardians of the woods in Tolkien's fantasy, creatures who became half-tree themselves over time.
The first few chapters will take you briskly through a set of unsettling perspectives on trees and forests: jungles are slightly wilder than forests; India's jungles have been curated over generations by the British and then by us, so there is very little of the original wildwoods left. In one rousing section, Mr Krishen whirls the reader through the acacia wars, where African botanists protested when they were told that only Australian acacias would be called by that name, while Asian and African trees would be renamed. Some of this, especially Mr Krishen's short history of forestry, is so compelling that you wish he'd added another 50 pages of text to the handbook.
But as I went through Jungle Trees and Trees of Delhi, it was not just the joys of naming the world around us, or even the naturalist's passion for his subject, that made me happy to have these books.
It is so easy to forget to slow down, and to look at things carefully, when our lives are so rushed. As I went through the photographs of hadua and hingot flowers, lingered on the structure of toothed and not-toothed pinnate leaves, it seemed to me that, except for photographers and artists, adults tend to lose the habit of paying attention to the world.
In one of her startling essays, Annie Dillard - who has made a writing life of paying close attention to things - writes about encountering a weasel while out on a walk. The glance they exchanged, woman and beast, was a long one, and she felt it as "a bright blow to the brain", a reminder of a world beyond the narrow confines of strictly human concerns.
Reading Ms Dillard helped me to see Mr Krishen's life more clearly, and to better appreciate his stunning and thoroughly astounding books. The point of going for a walk, or of exploration in general, Ms Dillard says, is not to see the most spectacular anything. "We are here on the planet only once, and might as well get a feel for this place." Mr Krishen joins the short but impressive list of naturalists in India, from Valmik Thapar to Salim Ali and M Krishnan, who do that better than anyone else.
Disclaimer: These are personal views of the writer. They do not necessarily reflect the opinion of www.business-standard.com or the Business Standard newspaper