"A culture is no better than its woods," the poet W.H. Auden once wrote, and if he was right -- and he was rarely wrong -- the prognosis for the 21st century is grim indeed. By 2030, many scientists estimate, more than two-thirds of humanity will be jammed into so-called megacities. Deforestation efforts have already stripped clear wide swaths of the Earth. Global warming looms large. Is it possible that we will soon be forced to reckon with a postnatural landscape?

That question -- danced around, but never explicitly voiced -- casts a gray-green pall over "Wildwood," the extraordinary new memoir by British environmentalist Roger Deakin, who died in 2006, shortly after completion of the book. "Woods, like water, have been suppressed by motorways and the modern world, and have come to look like the subconscious of the landscape," writes Deakin. "[The forest] still touches most of us not far beneath the surface of our daily lives."

A decade ago, Deakin donned a pair of trunks and dove into nearly every stream, lake and pond from the west coast of England to East Anglia. "Waterlog," his 2000 account of those adventures, was a hit in the United Kingdom, mostly by virtue of its quiet grace. Deakin was never an ardent environmentalist. He did not preach, he merely observed, and hoped that in the observing, readers would share his passion.

"Wildwood," a meditation on the "residual magic of trees," is a similarly elegant achievement. Deakin's sentences are sometimes sinuous and always supple; they bend back upon themselves like branches in the breeze. Here he is, for instance, on wandering through an apple orchard in Kazakhstan: "I am in that bemused state when you no longer comprehend what exactly is going on, but quite happily luxuriate in the sheer richness of everything ... the rose capped mountains, the bustling villages, the shadows of poplars, as you would in a dream."

The book is loose in form, split nominally into essays on the woodlands of central Asia, Australia and Europe, among other far-flung locales. But each section contains its fair share of earthy digressions. Deakin is always thinking about the woods, and a particular wood often reminds him of all woods, and then he's back again in England, lying on the forest floor, staring up at the latticework of leaves above.

Still, the breadth of "Wildwood" and the sheer force of its passion are something to cherish -- not in spite of Deakin's wandering prose, but because of it. The chapters may be circuitous, and yet they lead back to the same, moss-green place. "To enter a wood," Deakin insists, "is to pass into a different world in which we ourselves are transformed."

Matthew Shaer is a staff writer at the Christian Science Monitor. He has written about books for the Los Angeles Times, the Boston Globe and the Village Voice.