Call it botany as an extreme sport.

In 1867, the 29-year-old naturalist John Muir embarked on a trek from Kentucky to Florida, rhapsodizing about “divine beauty” over 900 miles on foot and another 100 by boat. The experiences and flowery observations recorded in his journal gave us “A Thousand-Mile Walk to the Gulf,” and the advent of the modern environmental movement.

Now, 150 years later, Atlanta journalist Dan Chapman has retraced those steps to assess the health of the verdant region he loves. How would Muir react to our contemporary landscape? “He would cry in his beer today,” writes Chapman.

However, Muir likely would nod his approval at the work of his acolyte. Chapman was a journalist for 30 years, including a stint at The Atlanta Journal-Constitution. Now he writes about conservation in the South for the U.S. Fish and Wildlife Service. For his first book, “A Road Running Southward,” he has produced an engaging hybrid — part lyrical travelogue, part investigative journalism and part jeremiad, all shot through with droll humor.

Who was John Muir? The Scotland-born “father of the national parks” and founder of the Sierra Club is obscure enough to all but eco-warriors to warrant a brief history at the start of the book, where Chapman sets the tone in a narrative voice full of attitude.

“Any deep dive into understanding John Muir’s rebellious life leads to one overriding conclusion: He was a hippie,” Chapman writes. “The shaggy, poetry-spouting, draft-dodging Bohemian thumbed his nose at conventional wisdom, religious orthodoxy and societal mores. … Muir shredded the 19th century maxim that all progress is good progress. He didn’t trust The Man — or, in his words, ‘Lord Man’ — and society’s money-first mentality. Confronted early on with good jobs and a bourgeois life, Muir recoiled. And then went hiking.”

(In some ways, though, Muir was very much a man of his times, given to ugly, racist outbursts, even as Black people shared their food with him.)

Between these two note-scribbling wanderers, it is hard to tell who is more enraptured by the outdoors, but Chapman is the bigger wiseacre. He takes an immersive, sometimes mischievous approach, occasionally sipping rye to warm his bones, spelunking in Mammoth Cave and swimming in one of Florida’s dwindling crystalline springs. His easy enthusiasm is infectious enough to make ardent tree huggers of us all. “The mountains are my playground, gym, church, happy spot and therapist’s couch,” he writes.

Like a good reporter, Chapman has done his homework, reading all of the dry scientific journals and surveys, connecting the dots, and distilling them into accessible observations and larger truths.

The South boasts an even bigger bounty of natural riches than many of us realize, with teeming biodiversity comparable to the Amazon. More than 90% of the country’s bird species live or pass through here. Nearly two-thirds of all U.S. species of fish live in our streams, and more than a quarter of the freshwater varieties are found nowhere else on earth. One of every three plant species calls the Southeast home. Then there are the mussels, which receive special attention for their vital filtration role. More than 90% of the country’s mussels, and 40% of the world’s, inhabit our waterways. All of this flora and fauna, though, could use better stewardship.

“While the Southeast region is home to 30% of the nation’s threatened and endangered species,” Chapman writes, “it receives less than 1% of all federal and state moneys spent nationwide trying to save those species.”

Not surprisingly, storm clouds loom on the horizon, just as they did in Muir’s time as he poked around a place still in ashes from the Civil War. “‘The Mountains Are Calling’ — And They’re Not Happy” is one chapter heading. The malefactors are the usual suspects — climate change (this book should be required reading for deniers); corporate polluters doing their usual pillaging and plundering; a widespread invasion of non-native species; and the inexorable phenomenon that would make Muir rend his tattered garments in Atlanta traffic — sprawl. With rising temperatures and sea levels, many plants and animals are seeking higher ground and cooler weather, and they are running out of room.

Muir is usually associated with Yosemite, but he experienced a “transformational moment” here on the east coast. Chapman starts his journey by camping in Savannah’s Bonaventure Cemetery, where Muir stayed while waiting for funds from his brother. It was here where his “environmental, ethical and philosophical beliefs that undergird the American conservation movement took hold … this passionate defender of all things wild owes much of his life’s work and reputation to the dead.”

Part of the charm of this picaresque is Chapman’s celebration of creatures that are not cuddly and photogenic. It takes a deft writer to make cave crickets sexy or bivalves entertaining (they are “sex machines,” Chapman writes), but these animals are keystones in the ecosystem — we lose them at our peril. The phrase “canary in a coal mine” gets deployed by multiple experts about an array of at-risk species.

Chapman also puts a human face on these developments, talking with people who revel in getting their hands dirty — scientists, oystermen, a sharpshooting feral-hog hunter, riverkeepers and a quirky, professional Muir impersonator, to name just a few. He crafts scrimshaw-like sketches of them all. The passage about a once robust laborer debilitated by coal ash is especially affecting in its subtlety: “Somebody else cuts the grass. The golf clubs sit in a corner of the garage. … He’s got seven grandkids who’ll never learn about hunting and fishing from their grandpa.”

“A Road Running Southward” offers no pat prescription to fix these problems overnight, but it reminds us of all that we have, and it sounds a powerful, resonant alarm.


NONFICTION

‘A Road Running Southward: Following John Muir’s Journey through an Endangered Land’

By Dan Chapman

Island Press

256 pages, $28

AUTHOR APPEARANCE

Dan Chapman. 7 p.m. June 2. Free. Presented by A Cappella Books. Manuel’s Tavern, 602 N. Highland Ave., Atlanta. www.acappellabooks.com