The Wild Places
by Robert Macfarlane
352pp, Granta, £18.99

As WG Sebald's reputation took shape in the years after his tragic death, his writing was much praised for its originality. But in truth what felt new in his work had as much to do with subtle adaptations of tradition as it did with pioneering a brand new kind of non-fiction. The Rings of Saturn, for instance - in which a descriptive ramble along the edge of East Anglia is interspersed with more or less freestanding reflections on characters and ideas - has its roots in late 19th-and early 20th-century travelogues of the kind written by Edward Thomas. For a long time, these books have generally been considered unfashionably occasional (Thomas dismissed a lot of his own work as "hack writing"). Now, thanks to their informed fascination with environmental matters, and their habit of combining different genres, they seem more interesting again.

Robert Macfarlane doesn't mention Sebald in The Wild Places, his follow-up to the elegant and highly successful Mountains of the Mind, but his method owes an obvious debt - as it also does to the traditions on which Sebald drew and to Thomas in particular. His account of visits to various remote places in order to evoke their spirit of wildness is punctuated with reflections on climate change, on destruction of habitat, on individuals met along the way and others who hover in the wings of history, on kindred-spirit writers, and on larger matters of time and belonging. In this respect, Macfarlane places himself in the company of people such as Iain Sinclair and Mark Cocker, who have also drawn on late-Romantic models in their own work. The Wild Places is a book that inhales the zeitgeist, as well as the fresh air of open country.

Sebald's prose is permanently conscious of the distance between self and surroundings: he is quintessentially one of Thomas's "superfluous men". Macfarlane also feels on the outside of things. This is partly because wildness in early 21st-century Britain is a hard thing to find - pushed to the margins (or so he begins by thinking), where it has not been entirely vanquished by pollution and modern farming and population growth. Then there are the difficulties created by the shortcomings of language to express what he feels, and the problems of containing a proper emotional response to a landscape within a more analytic appreciation of its qualities. "I could not explain what it really looked like," he says early in the book, when visiting an island cave, "certainly not what I was doing there, among the red and purple basalts." Later, the same note returns: "Open spaces bring to the mind something which is difficult to express"; "we find it hard to make language grip landscapes that are close-toned".

This is a common complaint in "nature writing" from Wordsworth onwards. But where it prompted Sebald to create a very particular and rich melancholy, it goads Macfarlane into a more strenuous kind of writing. He is a dab hand at coining bright images (in the Burren he sees "dozens of trees standing in their own reflections, like playing-card kings"), his vocabulary is deep and diverse ("sinters", "lenticles", "fletched", "sigil"), and his mood is generally close to rapture. The benefits are intense watchfulness, well-directed cleverness, and a likeable sense of deep engagement with his subject. The disadvantages are a slight monotony of tone, a tendency to over-writing or quaintness (looking "upon" something rather than simply looking "at" it) and - cumulatively - a complicated sense of self-effacement. Macfarlane's sight is very sharp and his mind very nimble, but like others writing in this vein before him, he keeps finding that these very qualities are partly responsible for holding him at a distance from what he loves.

That said, The Wild Places does map a change of heart as it also maps the route of his travels. To start with, Macfarlane is convinced that if he is to find any remaining wild places in our overcrowded archipelago, and thereby allow himself "to step outside human history", he must take himself to far-flung moors and mountains and islands. "We are," he says during a chapter set in Cumbria, "as a species, finding it increasingly hard to imagine that we are part of something which is larger than our own capacity ... We have in many ways forgotten what the world feels like."

In certain predictable ways, his early travels provide him with "the real" that he wants. On the island of Ynys Enlli, off the westernmost tip of the Lleyn Peninsula, he identifies with the contemplative and austere connectedness of the original peregrini - the monks and other devout solitaries who settled there. In Coruisk, the loch-filled valley on the southwest coast of the Isle of Skye, he encounters "a silence that reached backwards to the Ice Age" (similar sorts of time-travel occur in later chapters as well). Making "an ice-bound traverse" of Rannoch Moor, trekking through the Black Wood east of Rannoch, teetering on cliffs that define the north coast of Scotland and contemplating the peatbogs (the "Flows") nearby, he is at once taken out of himself and connected with the original need for his journeys. They are all places that put human achievement in the perspective of eternity and generate a sense of the primitive that is salutary and bracing.

Macfarlane's thinking about the nature and survival of wildness has changed by the time he gets halfway through his book. Sleeping out under the stars near Strathnaven, his original vision had "started to crumble from contact with the ground itself", mainly because this contact persuades him that "the human and the wild cannot be partitioned". In the Burren, and thanks partly to the influence of the late Roger Deakin (of Waterlog fame), a friend who accompanies him on the trip, he begins to understand that wildness is not inevitably to do with isolation and extent. As they lie face down on the limestone Burren, peering into a gryke (a fissure) in the surface, Deakin points out that what they can see below them is just as "beautiful and complex ... as any glen or bay or peak. Miniature, yes, but fabulously wild". As Macfarlane broods on this, he recovers some of the optimism about his subject that had been challenged on the high peaks. "Down in the gryke ... I had seen another wildness at work: an exuberant vegetable life, lusty, chaotic and vigorous. There was a difference of time-scheme between these kinds of wildness, too. My sense of a landscape's wildness had always been affected by the gravitational pull of its geological past - by the unstillable reverberations of its earlier makings by ice and fire. The wildness of the gryke, though, was to do with nowness, with process. It existed in a constant and fecund present."

Macfarlane refines this insight through the last sections of his book, in which he visits landscapes that are more hospitable and therefore more surprisingly full of surprises. In the deep time-scooped pathways of Dorset, in the approximately Sebald country of the Norfolk and Suffolk coast, and on the saltmarshes of Essex, he says (again) that he feels "a sense of wildness as process, something continually at work in the world, something tumultuous, green, joyous". The writing is just as vigilant as it was in the earlier, craggier chapters, and the structure similar (evocations of his walkings and open-air sleepings mixed with accounts of kindred spirits such as Stephen Graham, Ralph Bagnold, JA Baker and the largely forgotten but fascinating-sounding Vaughan Cornish, author of Waves of the Sea and Other Water Waves, 1910). But the mood is gentler, the self-driving less evident and the discovery and release of the self therefore more nearly complete.

It means, among other things, that The Wild Places is an odd addition to today's books about the environment: a consoling thing, as well as an admonitory one. It's not just that Macfarlane finds certain kinds of satisfaction for himself - creating, as he promised to do at the outset, a map in which the priorities of motorists are replaced by sites of natural wonderment, and discovering that wildness is not inevitably "about asperity, but about luxuriance, vitality, fun". He also encourages his readers to feel that while many of our fundamental connections have been broken or lost, many remain - if only we have the sense and tuned senses to appreciate them. This may not seem a particularly striking conclusion but it's well worth saying. And the journeys to reach it are so vigorously animated, they are well worth taking with him.

· Andrew Motion is poet laureate. His memoir In the Blood is published in paperback by Faber