John W. Reid had what he calls his “epiphany moment” sitting on a granite dome in the Upper Rio Negro in Brazil’s Amazon Basin.

He had taken a break after 18 years of running his own environmental nonprofit to spend four months in South America. He remembers “looking out over the biggest blackwater river in the world. In every direction I looked there was forest to the horizon.”

“The epiphany was manifold,” he said. “One is, there’s still a lot of forest in the world — not all is lost. Second, there have (been things) done that are working to preserve the forest.”

Back in the U.S., Reid was advised by a friend at the MacArthur Foundation that he should get in touch with distinguished conservationist Thomas E. Lovejoy, who had similar ideas about the importance of Earth’s big forests. From this partnership grew their new book, “Ever Green: Saving Big Forests to Save the Planet,” completed before Lovejoy died of pancreatic cancer at his home in Virginia in December.

Reid, who lives in Sebastopol, spoke with The Chronicle via video chat about what he hopes readers take away from the book, out Tuesday, March 29, and his collaboration with the late Lovejoy.

Q: “Ever Green’s” core message is that Earth’s survival in the face of global warming depends on its megaforests. What are megaforests, and why are they vital?

A:我们定义megaforests为基于“增大化现实”技术的森林生态系统e continental in scale and that contain large areas undisturbed by roads, by factories, by industrial farms. They interact — ecologically, physically, chemically — with the atmosphere at large scale, feeding weather patterns, storing carbon and giving space for unique human cultures to thrive.

Q: You focus on five megaforests. What and where are they?

A:Let’s start with something topical: Russia. Its taiga is the world’s largest megaforest. It has all these completely wild species, like deer with fangs, and tigers. Then we have the North American boreal, a big sweep of forest that goes from Alaska through Canada around the southern end of Hudson Bay to the Atlantic.

The Amazon is the biggest of the world’s tropical forests. It’s amazing in every dimension. It has the most diversity of species. It has a huge diversity of people. It has 20% of the world’s fresh water.

The second largest tropical forest is the Congo. It has the largest animals of any of the tropical forests. It has three different species of gorillas. It has chimpanzees, it has bonobos, it has elephants.

New Guinea is the smallest of the five.

Q: “Ever Green” argues these forests are key to reducing climate change because they reduce the carbon we put into the atmosphere. How does that work?

A:All plants are made of carbon — they get the carbon from the atmosphere. When they photosynthesize, they take in CO2 and use the carbon. The more plants, the more total biomass, the less carbon in the atmosphere. The intactness of these forests allows them to store a lot more carbon. That’s a good thing.

Q: The development pressures on these forests are enormous. What are the main threats?

A:The most important threat is the building of new roads. They’re the vectors for mining, for the conversion of forest to cropland, for logging and for oil and gas.

Q: You argue that these forests are key for preserving biodiversity, right?

A:Intact forests are the evolutionary workhorses of our world. You feel that when you go to the Congo and walk into the forest and you’re confronted by groups of chimpanzees and gorillas hanging out in the treetops. There are thousands of them, and they’re doing well because the forest is intact.

Q: You write that big forests also preserve cultural diversity.

A:Tropical forests in particular have provided a very productive environment for human diversity. The best example is New Guinea, where you have over a thousand languages. If you lose the intactness of the forests, those communities lose the ability to choose to live according to their own culture.

Q: You also say that Indigenous peoples are key to saving these forests.

A:Absolutely. Brazil is a good example. When you see “Brazil” and “forest” in the same headline, it’s usually something terrible. But when Brazil rewrote its constitution in 1988, an area the size of our national forest system was designated Indigenous territories. They are stewarding those areas. A third of the carbon on Earth is under some form of Indigenous management.

Q: What are the steps governments should take to preserve these forests? And are those steps economically realistic?

A:First, support the stewardship of Indigenous peoples. Second, dramatically expand forest protected areas while respecting local peoples’ forest-based livelihoods. Third, keep remaining forests as roadless as possible.

These steps are all economically viable. The sums needed to save megaforests can be as little as one or two dollars per acre.

Q: It must be bittersweet, “Ever Green” appearing a few months after the death of your co-author, Thomas Lovejoy. He had a distinguished conservation career, doing research in the Amazon and helping found the field of climate-change biology. What was it like working with him?

A:A huge privilege. He was nothing less than an icon. No one would ever say Tom seemed old, even when he was 80 and had cancer. He always had this great, boyish energy and sparkle.

Ever Green: Saving Big Forests to Save the Planet
By John W. Reid and Thomas E. Lovejoy
(W.W. Norton; 320 pages; $30)

Bookshop Santa Cruz and the Humanities Institute at UCSanta Cruzpresent John W. Reid:Online discussion. 6 p.m. Tuesday, March 29. Free.www.bookshopsantacruz.com