WHILE we talk, novelist Richard Powers is gazing out at his “backyard,” which is larger than your average, white picket-fenced suburban plot since “it covers 800 square miles and a half-a-million acres of forest”.

“Yeah, it’s big,” says scientist-turned-author Powers, clearly amused and delighted when he hears my intake of breath after I ask what he can see from the windows of his home in the foothills of the Great Smoky Mountains. The views are ravishing -- some 120 species of trees flourish here. But then, he explains, there are six different kinds of forest on his doorstep, about one quarter of which is uncut.

“There are more trees here than there are in all of Europe, from the Iberian peninsula to the Baltic states. There are 2,800 miles of mountain streams so three or four times a week I get out there and just walk,” he says, before quoting Dunbar-born, Scottish-American naturalist John Muir, who is one of his heroes and who is a presence in his magnificent new novel The Overstory. “Muir said, ‘We all walk the Milky Way together, trees and men... In every walk with nature one receives far more than he seeks’.

“By the way, I am not quoting Muir to you because I am coming to Scotland for the Edinburgh International Book Festival -- which I’m very excited about -- but because Muir is about as close to a secular saint as you can get. He believed, ‘The clearest way into the universe is through a forest wilderness’. This place would be strip mall without his advocacy and writing,” says Powers, who does not “just walk”, but also writes -- brilliantly.

It was here in his home at the foot of the Great Smoky Mountains National Park that he completed The Overstory, his 12th work of fiction and, I think, his masterpiece, about the natural world and our relationship to it, filtered through the lens of environmental activism.

The story spans American life from the antebellum era to the late 20th century, and is told through the concentric lives of nine strangers. They range from a psychologist to a paraplegic computer game designer (a job Powers did in a previous existence), from a homeless vet to an artist who has inherited 100 years of photographs of a doomed American chestnut tree. There are five others besides these, although the most compelling characters are the majestic trees that link these lives that eventually grow together like the tangled narratives of a mysterious wild wood.

Those lives are the “understory,” the low-growing plants and shrubs that flourish between a forest’s canopy and its floor. The overstory -- a word that takes on several meanings in Powers’ novel -- is the canopy that creates the understory’s environment and in his epic it’s a miraculous landscape filled with sentient beings. (Incidentally, the novel is printed on paper “from responsible sources”.)

Born and raised in Illinois, the

60-year-old, whose last novel Orfeo was longlisted for the Man Booker Prize, came east two years ago after living for many years in the mid-west. “I’d moved to California, to teach briefly at Stanford [University], which is where the idea for The Overstory took hold.”

What was the tiny seed that grew into his novel?

“I had always had this yearning to write a book in which the trees would be central characters but telling a story through human characters,” he replies. “The town of Palo Alto is right in Silicon Valley. When I was there, I saw this incredible concentration of wealth, invention and power: the corporate headquarters of Google, Facebook, Apple... It’s a little, concentrated strip where the future of the world is being decided in this go-go culture created by super-smart people. They have this technical optimism, they believe that all problems are going to be solved and that they’ll live forever. It’s kind of the best and the darkest aspect of the human desire to take control of the world.

“On the other side of town are the Santa Cruz mountains, covered in second-growth redwood because [the trees] were cut down to rebuild San Francisco in the late 19th century. People realised, however, that this was a unique system that had to be left alone, so they set up this preserve. What a redwood can do in 100 years is pretty stunning! Mind-blowing! Majestic! Sublime!

“To escape the craziness of Silicon Valley I would go up into those mountains. One day I was walking around and I came across a single redwood that had survived -- it was like finding a blue whale in the middle of a pile of dolphins. I realised that what I was seeing was not the original forest but that I was having this tiny glimpse of what the world looked like before our world. That’s where The Overstory started. It was the contrast, the tension between these two worlds -- the sheer power of capitalism and the world before its incursion.”

Powers spent about four years writing multiple drafts of his novel. In the course of researching the book he read about the Great Smoky Mountains, the largest remaining tract of virgin forest left in the eastern US. “I thought, ‘I have to go see this just to get a feel for it’, because 98 per cent or more of American forests went under the axe. There’s no way of knowing what the country looked like before there was any European contact, but here you move from one eco-system to another.

“When I arrived in this vast place I fell in love with it; I didn’t want to leave. It was a research trip but I felt instantly drawn to it and really wanted to stay. Two years ago I bought this house and have lived here ever since. The final composition of the book happened here and I am going to stay on because this feels like home now.

“I can honestly say The Overstory literally changed my life. This place -- one of the most biodiverse on Earth outside the Tropics -- has greatly changed the way I spend my days. I’ve found ways of opening myself up here, ways of releasing myself. It has absolutely changed the way I write. I listen much more and I look much more.

“This is my 12th novel and I’ve bounced around many topics: artificial intelligence, music, race relations, all kinds of different milieu. Every time I have finished one book I have been eager to go onto a new area of stories because I feel all my books are in conversation with each other. Now, after writing this book, I feel like staying in this same world and writing the same book again and again.”

So has his family moved there, too?

“Well, no, actually I don’t have a family, so it’s just me here, living alone in this astonishing place. The joy of it,” he says softly.

Garlanded with every known American literary award, Powers is the recipient of a MacArthur Genius grant and a National Book Award winner;

he’s also been a Pulitzer Prize and

four-times National Books Critics

Circle finalist. Magic Powers indeed, since he has a degree from the University of Illinois in theoretical physics and studied for a master’s in literature

while teaching himself computer programming.

He first felt the urge to write at the age of 32, after being an obsessive reader since childhood. His literary heroes remain Thomas Hardy and James Joyce. August Sander’s famous photograph, Three Farmers on Their Way to a Dance inspired his 1985 debut novel, which shares its title with the image. After swithering between careers, he had found what he wanted to do.

At the end of a long and fascinating conversation that ranges from his despair with Trump’s presidency to his sadness at the death of Stephen Hawking -- “a man with the vision of an artist who never lost his sense of wonder” -- I ask Powers whether he misses the world of science.

“What interested me most in studying physics was the notion of connectivity, but I don’t believe art is about emotions and science rationality. I believe both struggle to connect things that are outside of our experience. We have to know that we’re not alone. Programming and novel-writing are not so vastly different, nor science and art -- both are speculations about where we’ve been put down. Which is why The Overstory is such an urgent book asking whether we can go on living like this. All I can tell you is it’s been a unique experience writing this novel,” he replies.

“Working on such salubrious subject matter has been joyful.”

The Overstory, by Richard Powers (William Heinemann, £18.99). Powers will be at the Edinburgh International Book Festival in September