At the same time, there are valid ecological reasons to include introduced species in a garden, too — a point that even Tallamy concedes. The interactions between native plants and herbivorous insects on which he fixates, while undeniably important, are still just one aspect of any green space, cultivated or wild. There’s so much more to consider.

The climate is now changing so rapidly that many species are struggling to adapt. Researchers have found that introduced species sometimes outperform natives in coping with the extreme and volatile weather that will increasingly characterize future climates. A consortium of experts based in part at the University of California, Davis, has highlighted certain trees, shrubs and flowers from Asia, Australia and South America, in addition to numerous North American species, as suitable choices for streetscapes and gardens in California’s Sacramento Valley because they are pest-resistant; noninvasive; tolerant of drought, heat and cold; and, in some cases, beneficial to local wildlife.

“This part of California used to be a grassland with historically few tree species,” says Emily Meineke, an entomologist at U.C. Davis. (She is not directly involved with the consortium.) “Given how much we need shade, can we really argue that we should only plant native? If we still want to have functional plant communities, I think we have to look at every avenue. I can’t imagine Davis transitioning to future climates without some component of introduced species.”

Non-natives can also significantly expand the resources available to pollinators. Insects, birds and other creatures that sustain themselves with pollen and nectar typically have more flexible diets than leaf-eating species because, unlike leaves, flowers evolved to attract animals. Yet many ecoregions have seasonal gaps during which few if any native plants are blooming. Introduced species can fill those voids, which is especially helpful as climate change threatens to push native pollinators and flowers further out of sync. Recent studies have also revealed that some garden cultivars are as attractive to native insects as their wild progenitors — and, in a few cases, preferred — possibly because their flowers are more colorful, longer-lasting or more alluringly shaped.

Other introduced species provide gardeners themselves with sustenance, medicine, beauty and joy. A majority of fruits, vegetables and herbs that U.S. gardeners enjoy growing at home evolved elsewhere and are now so dependent on intensive human care that they have essentially no chance of becoming invasive. Some natives spread or seed too vigorously to be practical in a typical urban garden or are too drab to suit most gardeners’ tastes, whereas many ornamentals are self-contained yet spectacular, enthralling us with radiant hues, intoxicating scents and exquisite patterns that natives cannot always match.

On a recent day, Mr. Frist spoke by Zoom from his office in Nashville, surrounded by photos and mementos. A map of Tennessee, rendered in green thread on reclaimed barn wood, to symbolize conservation, hung behind him. On his right wrist, he wore a wooden beaded bracelet from the Loisaba Wildlife Conservancy, north of Nairobi. Mr. Frist has visited Africa about 20 times, mostly for medical trips: In the Senate, he was crucial to the passage of the President’s Emergency Plan for AIDS Relief, PEPFAR, which funneled billions of dollars into the prevention and treatment of H.I.V. and AIDS abroad.

But one photo was especially important, he said. It was a portrait of his wife, Tracy Roberts Frist, and their Border collie, Bonnie, sitting on a woodsy ridge. The couple married in 2015 — it was his second marriage — and live on a working farm outside of Nashville, along with eight sheep, nine horses, three herding dogs, geese, goats, chickens and two donkeys.

They also have a 995-acre farm in Virginia that includes an arboretum and federally protected wetlands, where they raise grass-fed cows, and regularly host environmentalists, scientists and 4-H students. In 2024, they donated $1 million to fund an initiative for planetary and human health at The Nature Conservancy, the nonprofit where Mr. Frist chairs the global board of directors.

Mr. Frist said his wife helped him connect with the wild, natural world. She did her graduate studies in animal and human behavior, and oversees riparian and wetland restoration along with regenerative agriculture at their farms. “She is born of nature, is part of it, it is written into her soul,” Mr. Frist said.