Henry David Thoreau once heaved a big stone against the trunk of a chestnut tree to bring down a shower of nuts. He loved their sweet meat, but the meal filled him with guilt. “It is worse than boorish, it is criminal, to inflict an unnecessary injury on the tree that feeds or shadows us,” he wrote in his journal in 1855. “Old trees are our parents, and our parents’ parents, perchance.”

During Thoreau’s life, American chestnuts covered a huge swath of the Eastern United States. The author of “Walden” couldn’t have imagined that billions of our woody parents would be destroyed by a blight in the early 20th century. That decimation, sparked by a fungus imported from Asia, was compounded by the nation’s voracious lumber industry, which denuded North America and then lashed out across the world.

In 2016, Annie Proulx captured three centuries of logging in the New World with a fantastic novel called “Barkskins.” Given its enormous length and its encyclopedic examination of wood, “Barkskins” felt like a singular creation, but now it has a monumental companion planted right alongside it: Richard Powers’s “The Overstory.” This ambitious novel soars up through the canopy of American literature and remakes the landscape of environmental fiction.

Long celebrated for his compelling, cerebral books, Powers demonstrates a remarkable ability to tell dramatic, emotionally involving stories while delving into subjects many readers would otherwise find arcane. He’s written about genetics, pharmaceuticals, artificial intelligence, music and photography. In 2006, his novel about neurology, “The Echo Maker,” won a National Book Award. And now he’s turned his attention, more fully than ever before, to our imperiled biome and particularly to the world’s oldest, grandest life forms: trees.

“The Overstory” moves the way an open field evolves into a thick forest: slowly, then inevitably. For a while, its various stories develop independently, and it’s not apparent that they have anything to do with one another. But have faith in this worldmaker. Powers is working through tree history, not human history, and the effect is like a time-lapse video. Soon enough his disparate characters set out branches that touch and mingle: Before the Civil War, a Norwegian immigrant travels to Iowa and begins homesteading in the largely empty new state. Just after World War II, a young man sails from Shanghai to San Francisco. In the late 1970s, an odd kid from a troubled family gets accepted to college. And a sergeant in the Vietnam War barely escapes death when a 300-year-old banyan catches his body falling from a cargo plane. “He owes his own life to a tree,” Powers writes.

We all do.

That universal salvation is the root of this amazingly complex novel, which keeps expanding to include a video game pioneer, an intellectual property lawyer, an amateur actress, a woman back from the dead and many more. As in nature, there is what seems like extravagant excess. These characters don’t all snap together at some contrived moment like a literary flash mob, but “their lives have long been connected, deep underground,” Powers writes. “Their kinship will work like an unfolding book.” In one way or another, all their lives turn toward the miracle of trees.

What makes “The Overstory” so fascinating is the way it talks to itself, responding to its own claims about the fate of the Earth with confirmation and contradiction. Individual stories constantly shift the novel’s setting and pace, changing registers, pushing into every cranny of these people’s lives.

As is so often the case in Powers’s books, “The Overstory” includes a radical expert who hypnotizes us with the provocative implications of her field. Patty Westerford is a young botanist in the 1960s who discovers that “trees are social creatures”: They communicate with each other and react to their environment in dynamic and ingenious ways. (Patty’s ideas echo those of Suzanne Simard and Peter Wohlleben, popularized in the best-selling book “The Hidden Life of Trees.”) As we follow Patty’s tumultuous career from initial success to professional exile to eventual sainthood, she becomes the novel’s — and, one suspects, the author’s — green prophet. Like a double helix of Jane Goodall and Rachel Carson, Patty is that rare, cutting-edge scientist whose work reaches far beyond the lab and inspires a kind of mystical awe.

Some of the characters moved by Patty’s revelatory research are inspired to more aggressive forms of environmental activism — even ecoterrorism. In harrowing scenes of personal sacrifice — or deadly self-righteousness — we see an unlikely group drawn together by their absolute conviction that our rapacious destruction of trees is an act of mass suicide.

The urgency of that belief gives rise to the novel’s most unsettling theme: the tension between complacency and stridency in the face of existential threats. One character, a deeply conflicted psychologist, dedicates his life to researching “the personality factors that make it possible for some individuals to wonder how everyone can be so blind.” Who’s crazier, he asks, those protesters camping on top of a doomed redwood or the mass of consumers ignoring the flames of their only planet? It’s a question the entire novel grows around with fairly bleak expectations.

“All good stories,” Powers writes, “kill you a little. They turn you into something you weren’t.” That’s a daunting standard for any author, but it’s the feeling one has emerging from the forest of this remarkable book.

Ron Charles is the editor of Book World and host of TotallyHipVideoBookReview.com.

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the overstory

By Richard Powers

W.W. Norton. 502 pp. $27.95