Big Tree, Small World

In his new book, Doug Tallamy looks at oaks as a life force.

Interview by Bradford McKee

Doug Tallamy. Photo © Rob Cardillo Photography.

In two influential books, the entomologist Douglas W. Tallamy has spread a message of people-powered biodiversity, to say that if humans have crowded out nature across the world, they can also invite it back in at close range. Tallamy, who is 70 and lives in southeastern Pennsylvania, is a professor in the Department of Entomology and Wildlife Ecology at the University of Delaware, where he joined the faculty in 1981 and has led or coauthored 104 published research studies on the behavior and chemistry of insects. In 2007, his book Bringing Nature Home: How You Can Sustain Wildlife with Native Plants hatched a mission to persuade home gardeners to think big about the buffets they can create for animals just outside any door as bulwarks against ecological decline. He expanded that project in 2020 with Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard, which became a New York Times best seller.

Tallamy’s latest book, The Nature of Oaks: The Rich Ecology of Our Most Essential Native Trees (published, like the others, by Timber Press), puts his message through a different prism, that of the genus Quercus, which includes 435 species of oaks around the world, 91 of them in North America, where they are superlative among trees as sources of food and shelter in their environments. He details the oak’s life cycle through the 12 months of the year. “Unfortunately, the diverse web of life that is associated with oaks goes unnoticed and thus unappreciated by most homeowners,” Tallamy writes. Many homeowners, indeed, are ready to cut down oaks to avoid raking leaves, though he explains that raking is not only unnecessary but to be strongly discouraged, given the high value of oak leaf litter as microhabitat. Once again his gift to readers, in plainspoken prose, is to help them see the familiar in nature and find the unseen.

This interview has been edited and condensed.

Bradford McKee: In The Nature of Oaks, as in your earlier books, you’re bringing science and natural history to the household conversation—

Doug Tallamy: That’s the goal!

BM: —though scientists who do academic research and also do public advocacy so regularly are exceptions in most fields. What’s driving your mission?

DT: It’s really important because we’re at a critical tipping point with climate change. The headlines demonstrate it. The United Nations says we will lose one million species to extinction, possibly in the next 20 years. When are we going to react? When everything is gone? It is time to act. That’s what motivates me. The public’s listening. We’ve got a global biodiversity crisis, but it’s got a grassroots solution, and the grass roots are listening. The solution includes land managers—anybody who owns land anywhere and land managers who can change this adversarial relationship with nature. We have to have landscapes everywhere that support natural systems. We’re not making this up. It works. There’s one other factor. Why am I doing this, and not somebody else? It’s the right stage of my life. Nothing was in place when I was trying to get tenure. This is not the road to tenure in academia. I’m looking at retirement and have freedom other academics don’t have. And citizen science is not frowned on as it was when I started out. That doesn’t mean I stop publishing in real journals. There’s a conflict—do you spend your time writing and talking to academics or to the public? I can err on the side of the public.

BM: You’re a bug guy who chose to write a book about a certain kind of tree. The topic of oaks takes us to so many things related to your insect expertise. How did you arrive at the oak as a vehicle for all this action?

DT: It’s a long road. I’ve always liked oaks, but in the course of the last 15 years, we’ve come to realize how important oaks are in terms of supporting the food web. E. O. Wilson said insects are the littlest things that run the world. Oaks in North America are the best at supporting insects. Oaks support at least 952 species of caterpillars. So there’s that. But then, most people are not into caterpillars, so there are other things, like the acorns that get so many creatures through the winter. Landscapes should do four things. They should support the food web. Another thing would be managing the watershed. Everyone lives in a watershed, and it must be managed everywhere. Oaks have these great root systems and are ideal for managing watersheds. Landscapes should also lock up carbon in plant tissues and store extra carbon in the soil. Oaks are way up there in that regard. The final thing is, landscapes must support a complex community of pollinators. OK, oaks are wind-pollinated, but three out of four is pretty good. I’m not writing about a tree but about a community of organisms that are focused on one plant. You plant an oak in your yard, you’re planting a zoo. It’s your chance to create life that didn’t exist on that space. I wrote the book because nobody knows that. People say, “I’m gonna not plant oaks because there are too many leaves to rake in the fall.”

A mature oak can shed 700,000 leaves, which decay slowly to provide shelter, food, and moisture to decomposer species and their predators. Photo by Doug Tallamy.

BM: A theme of this book is the stalwartness of the genus Quercus, particularly in the modern world. Let’s talk about the implications of that—its resistance and vulnerabilities to its rapidly altering environments, and what it indicates about the current state of the climate more broadly.

DT: We as a civilization have relied on oaks for quite a while. I’m not even sure if it’s in the book, but the ink in our history was written—the Bible, the Magna Carta, the Declaration of Independence—written in ink that came from a gall produced by oaks. If you look at the history, why was England so focused on the New World? It’s because they had chopped down all their oaks and needed a new supply for their navy. Look at Notre Dame. They’re replacing the roof made of oak, 600 large oak trees from France. So, we still rely on oaks, but they’re not as resilient as we need them to be. There’s oak wilt, leaf scorch, sudden oak death, all these different threats in different parts of the country. Eastern forests have 50 percent fewer oaks now than 100 years ago. People relied specifically on very old oaks, and they thought if you had a hollow in the trunk that you had to take it down. But that’s normal! Lots of animals live in there. A third of oaks globally are threatened with extinction, endangered, because many of them had very small ranges that are being “developed.” Twenty-eight of our 91 North American oak species are threatened.

The ambiguous moth, Lascoria ambigualis, is among 70 litter moths that feed on dead leaves rather than live ones. Photo by Doug Tallamy.

BM: In the book, you make a lot of offhand climate references—to subzero nights and January days at 20 degrees Fahrenheit. Are those temperature norms changing at your place in southeastern Pennsylvania?

DT: We’ve been here 20 years. We’ve seen changes. Nothing like the ecosystem-threatening changes you’re hearing about. We’ve had cool, wet springs several years in a row, though the falls are warmer later. We’re not getting hotter temperatures, just more hot temperatures. Places suffering from climate-induced problems are the far West with the megadrought, like Arizona and California. They’re adapted to hot and dry, but it’s tougher now. I keep a close tab on the insect populations at our house. Several years ago, we had a storm that dropped seven inches of rain in three hours, and three inches of that in 45 minutes, and it just scoured everything like a fire hose. Our moth populations were devastated, and it has taken several years for them to recover. But this year, we have more moths than ever. If I were only measuring insects on our property, I would conclude that there is no insect decline. This tells me that if we put back the plants that insects need, we can reverse the declines other people are measuring. We have increased biodiversity here. I’ve been taking a picture of every species of moth on our property—1,114 species on our property, 44 percent of all the moth species in Pennsylvania, and we’re on 10 acres, on 1/240,000th of the area of Pennsylvania. Because we put the plants back. We have recorded up to 60 species of birds that have bred on our property—not flybys but nesters. A lot of the disastrous headlines we are seeing are reversible if we put the plants back.

BM: You emphasize the superlative place oaks have as a resource to so many other organisms and processes, such as to oak-specific feeders and also for watershed management. And then you mention that zelkovas are not so hot as animal hosts. There’s an entire block next to mine lined by a canopy of zelkovas. Are they doing any good?

DT: They looked like the elms we lost, so to replace the elms with something visually similar, we brought in another plant from Asia that supports nothing. It’s going to be a major invasive species. I got to my mother-in-law’s retirement community, and it’s all zelkovas, and the woods across the street are showing up with zelkovas. Elms are resistant [to disease] more and more, and we should be planting a lot of them.

Oak species have diverse leaf shapes and sizes. Oaks in arid locations tend to have smaller, thicker leaves than those in cooler, wetter regions. Photo by Doug Tallamy.

BM: You also write critically about the unproductive qualities of yards and gardens planted with nonnative ornamentals. Can gardeners have it both ways—say, keep the Korean spice viburnum, but offset by milkweed and native rhododendron?

DT: A typical suburban landscape in Maryland, Pennsylvania, and Delaware is 92 percent lawn. We’ve measured it. That’s not a horticultural masterpiece. We just don’t know what to do with it. Can that be improved? Absolutely. Cut it in half. It’s an area rug. There’s a lot of things you can do productively with lawn. Anybody can work on that. My former PhD student Desiree Narango did research in D.C., where she was asking, what does it take to sustain a population of chickadees? You need 70 percent of the woody plant biomass to be native, or chickadee death rates exceed birth rates. But that other 30 percent gives us room for compromise in our plant choices. You can have your ginkgo and forsythia and boxwood, and you can have it without destroying the productivity of your landscape. It’s not the presence of nonnatives. It’s the absence of natives that support wildlife. You can add color and not destroy the foundation of the food web, which is the keystone plants, the 14 percent of the native plants that are making 90 percent of the food. Eighty-six percent of natives are contributing, but not all that much. So, if you have the keystone plants [oaks, cherries, willows, birches, hickories, pines, and maples are mentioned in the book], you’re doing well.

BM: You’ve also written about the relative value of cultivars of native plants.

DT: It’s about productivity. We studied that. We didn’t look at flower traits. We looked at structural traits—tall plants that have been turned short, enhanced berry size, and so forth. The only trait that consistently reduced insect use was taking a green leaf and making it red or purple, loading it with anthocyanins. Annie White at the University of Vermont has worked with flowers on cultivars, and her results are not as rosy. We’ve got 4,000 species of native bees. A third are highly specialized to using pollen from particular flowers, and when you’ve changed the characteristics of those flowers, you’ve changed the whole picture. Pollination is complicated—it’s the pollen, not the nectar, that matters. Insects can use the nectar from many plants, though pollinator specialists need the pollen from particular plant species to reproduce successfully. You can have insects crawling all over your nectar makers, but they’re just sucking up sugar water and not getting what they need to reproduce.

BM: What specifically did you learn in writing this book? What changed or expanded your mind about anything?

DT: Expanded is a good word. I wrote Bringing Nature Home in 2005, and it was published in 2007. People would ask, why did you do this? I used to joke that I want to re-landscape the U.S. That’s not a joke, I realized. That’s exactly what I want to do. I want to re-landscape the world. This is a global issue. We act as though plants are just decoration, and we’re going to use them to decorate the world. It’s a deadly mistake, but it doesn’t mean we can’t have the decorations. In that way, my mind has expanded. One thing that’s made the biggest difference is discovery of the fact that there are these keystone species. We have this information for North America, but we want it for every place. We’re working on England now, and Germany. We want to say, here is a list; this is what to focus on. And that will definitely close out my career. If anybody has a couple million dollars, let me know.

BM: You end the book on a note about the threats of extinction, the ultimate concern. But you sound optimistic. Is that willed?

DT: I’m coming back to what I’ve seen here at home [in increasing biodiversity] and from e-mails I get from people who do it every day. You can bring the life back. It works. That’s what makes me optimistic. There are no giant forces. We’re talking about a cultural change, obviously. We can change culture—we’ve seen big cultural changes in haircuts. I see the public’s reaction to these headlines. When there was the insect Armageddon here, I didn’t think anybody would care, but I was getting e-mails from all over asking, what can we do? We’re getting past the notion that humans and nature are separate. People are getting used to the inevitable reality of humans and nature coexisting.

Bradford McKee was the editor of LAM from 2010 to 2020 and is now an editor at large for the magazine.


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