Notes from Walnut Tree Farm is set up as the journal of a year, month by month from New Year's Day (“I am lying on my belly in frozen snow and frosty tussocks in the railway wood”) through to December 31. This final entry is eerie, as the editors probably intended. Roger Deakin, the nature writer who died two years ago, describes the New Year's Eve walk he's just taken in the darkness, remembering the songs he used to sing with his father as they marched along: “‘John Brown's body lies a-mouldering in the grave ...' Now, as I turn back along the common, the wind is at my back, and I am no longer battling it. All is suddenly quiet and peaceful, and the wind is no more than a gentle hand on my back. Clouds riding the wind under the stars and the orange glow of Diss beneath them as they cross the common.”

The rhythms here mime those of a death, although this wasn't the paragraph with which Deakin said farewell to his readers. He died on August 19, 2006 at the age of 63, having just finished Wildwood, his book about trees. For the previous six years he had been jotting down random observations and research notes for various projects in lined exercise books, 45 in all. From them, Alison Hastie and Terence Blacker, the book's editors, have picked sentences, paragraphs and sometimes mini-essays and assigned them to the appropriate months, either from specific dates in Deakin's entries, or from context, and made up a pretty successful bricolage.

As with so much writing about nature since the late 18th century, there's a strong elegiac timbre tinged with the melancholy of a posthumous memorial. The reader knows before Deakin that, for this lively, energetic and busy fellow, bursting with plans for books and prospective odysseys, an early death from cancer is just around the corner. The world of Walnut Tree Farm is about to end, at least from an anthropocentric perspective, which surely was not that of Deakin.

He does not seem to have been much of a mushroom fancier, but Deakin's relationship with his 12-acre patch of Suffolk reminds me of one of the earth's largest living organisms, a 30-acre patch of forest soil in northern Michigan that is one vast underground mycelial network of Armillaria bulbosa, with the fungal spores and tree roots intertwined and mutually nourishing each other. Deakin thus communes - in the richest sense of the word - with the creatures of his old hedgerows, the living slime on the bit of Elizabethan moat in which he swam, his coppice wood, his unpoisoned pastures, the hornets in the attic, the badgers in their sett, the young hedgehog warmed back to health behind the Aga, the timbers of the old house itself.

He is vigorous in his natural descriptions, fearless in plunging into chilly streams and meres, but almost comically averse to immersing himself in the tides and currents of his own emotional life. From time to time, he grits his teeth and dips in his foot. There is a July entry that begins flatly, “I was 17 when a policeman came to our door and told me my father was dead.” He had been found on a Bakerloo line train at Euston Square underground station. “He just went out that morning,” Deakin goes on, “and disappeared out of my life...Thus did I acquire my sense of loss - a deep-seated feeling that has followed me around all my life and that I've never shaken off.” It is as though a previously taciturn Hamlet suddenly mutters that he has always been bothered by bad dreams. Then the made-in-England curtain of manly discretion falls again.

The journal entries were written, or at least edited, to give the sense of a man with plenty of friends, but living alone and sometimes lonely. “I need someone to fold the sheet,” runs an April entry, “someone to take the other end of the sheet and walk towards me and fold once, then step back, fold and walk towards me again. We all need someone to fold the sheet.” Human solitude amid the non-human kingdom of nature has sparked the most piercing poetry and prose down the centuries, from Yosa Buson's haiku (“Walking on cracked dishes/the rat's feet make the music of shivering cold”) to the American naturalist Doug Peacock's extraordinary trudges through the northern Rockies or southwestern deserts, often thinking of his friend, the author Edward Abbey.

There is an American substratum in much of Deakin's writing, infrequently explicit, but powerful nonetheless. His 1960s sensibility, his holism, owe a lot to Stewart Brand's Whole Earth Catalogue, the vade mecum of hippies, new agers and back-to-the-landers such as Deakin himself. He does pay homage to EF Schumacher's Small Is Beautiful, but although I may have missed it, not to Abbey himself, who shared so many of Deakin's rages at human destructiveness. But whereas Abbey at full power is like an organ in a cathedral, Deakin is better mannered, like a cello. I shall put Notes from Walnut Tree Farm on the shelf next to HJMassingham's Remembrance and the wonderful old Batsford books about the England whose ways Deakin honoured with such knowledge and such creative constancy.

Notes from Walnut Tree Farm by Roger Deakin
Hamish Hamilton £20 pp310

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