‘the hidden company that trees keep,’ with jim nardi

DR. JAMES NARDI says you can tell a lot about a tree by the company it keeps. From life in the soil around their roots to the action up in their canopies, trees are swarming with engagement—unseen microbes and fungi, countless insects and other arthropods, and vertebrates like birds, squirrels, and even porcupines.

Jim Nardi spoke about their diverse community of companions. He is research scientist in the School of Integrative Biology at The University of Illinois Urbana-Champaign, and the author and illustrator of several previous books. His latest is “The Hidden Company That Trees Keep: Life from Treetops to Root Tips” (affiliate link).

Plus: Enter to win a copy of the new book by commenting in the box near the bottom of the page.

Read along as you listen to the March 13, 2023 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).

the company trees  keep, with dr. james nardi



Margaret Roach: Welcome, Jim. Now you don’t just know all this and write all this, but you illustrate these two books of yours?

Jim Nardi: Yes, I do.

Margaret: Oh my goodness.

Jim: I find it very soothing and relaxing, and I learn a lot from such close observation that’s required in order to draw these creatures.

Margaret: Oh, the illustrations are just, I’m so charmed, I’m just so drawn in.

Jim: Thank you.

Margaret: And it’s funny, when I was reading the book and looking at the illustrations I was thinking of another favorite author, the biologist and prolific author, Bernd Heinrich, formerly from University of Vermont.

Jim: Oh, yes. Sure.

Margaret: And because he illustrates his, too. And so I thought oh my goodness, what talent [laughter]. So anyway, we’re going to talk about these big organisms, kind of I don’t know, are they the biggest organisms in our average world over here, these trees?

Jim: Well, yes. I think the record is held by a redwood tree. They can certainly be very large, but they can also be very ancient and very small.

Margaret: Yeah. But in our average world, those of us who are gardeners listening in our backyards, I mean, they’re the biggest creatures we see day to day, they’re the giants of the landscape. So you start the book with the sentence: “You can tell a lot about a tree by the company it keeps.” And so just to get us started, the range is from what to what, we’re tiny to what?

Jim: Oh well, we can begin with the viruses and then move on. The microbes, we’re discovering a new world out there that we didn’t know existed just a few years ago, and that’s the microbial world that’s associated with each individual—with not only ourselves, but with the trees and the small companions that they keep. Even small bacteria contain viruses and smaller bacteria within them.

Margaret: That’s very small [laughter].

Jim: Indeed it is.

Margaret: And as I said in the introduction, trees companions go up to mammals and other large animals and so forth. But where I am, black bear tend to like running up a tree. If they get a sight of you they go run up a tree.

Jim: Oh, how fortunate you are to have black bears.

Margaret: Yes. My best thing was the other day I had a mink in the backyard, swimming in the water garden that was semi-frozen, but that’s a digression.

Jim: What a treat.

Margaret: Crazy. Crazy. But a lot of the companions are insect species. And so I was fascinated in the book, you talk about the diversity, the great range, and certain tree species have a lot of diverse insects that engage with them, don’t they?

Jim: Oh, indeed. We usually think of the insects that feed on trees, but there are far more insects that prey on these plant-eating insects and even far more that are parasitic on these insects. And these help maintain a balance in the life of the tree that so many of us are unaware of—the importance of these predators and parasites in maintaining a balance in the life of the tree.

Margaret: And you also write about how lately, especially, we talk about boosting our immune systems and immune diseases and immune this and that, but we animal types aren’t the only ones with immune systems by any means. So the tree has this really incredible, impressive immune system as well. Yes?

Jim: We normally think of trees as passive creatures, however, they’re quite capable of mounting a robust defense, an immune response. And by immune response, we mean the ability to distinguish self from non-self. So non-self would include everything from other insects, microbes, the bite from a porcupine. And so they’re not only able to defend themselves with their own sophisticated immune system, but they’re able to recruit animal and microbial allies to help defend them.

Margaret: And I think if you asked gardeners, well, what allies do trees have? They’d probably say, “Oh, well, I guess some animals disperse their seeds, and some pollinate them.” They’d know that maybe, but they wouldn’t know all these other really complex ally relationships.

Jim: We know that birds help maintain, help control, the populations of the leaf-eating and wood-eating insects. But there’s a whole world out there of parasitic insects. And this is, in terms of diversity, it’s probably one of the most diverse: 15 percent of all animal species are believed to be parasitic insects, and parasitic insects make up about 10 percent of the number of species of insects.

These are incredibly diverse. Some of them are very specific; they have specific hosts on the tree. And some of them are generalists. There are flies called tachinid flies that whose larvae feet on over a hundred different species of tree herbivores.

Margaret: Wow. And it’s incredibly complex. And as I said, when we began speaking, the illustrations in the book really give you a look at some of these creatures, some of which are quite small or you may never have seen. And I loved, it’s not like one organism is getting all the benefit, or the other organism is the harmful one. We can’t put those judgements. It’s a complex sort of interaction, dance, whatever. I love one illustration in the book, there’s a bird in a nest tree—so it’s taking advantage of the protection of the nest to the branch to hang his nest on and the leafy protection. But it also gets advantages from being there and also provides services to the tree. Right?

Jim: Oh, indeed. Each of these birds will feed on, in its lifetime, will feed on thousands of caterpillars plant eating insects. And so the tree never has to worry about being, usually never has to worry about being defoliated with the help of its avian as well as insect allies.

Margaret: Right. And as sort of cryptic, as hidden as many of those insects, those caterpillars and so forth try to be in the book. You say “the birds leave no leaf unturned.” They look and look, and look. Right, they hunt out their dinner.

Jim: Oh indeed. And all the crevices in the bark and yeah, they’re very thorough and on the ground beneath the tree, among the leaf litter.

Margaret: The bark is something; the bark is really special. One of the ways that sometimes in winter, for our tree ID, we can start to tell what species of tree it is. But I live in a spot where outside my window, where I sit most days and work, my little home office is this very, very old triple-trunk Thuja, very giant tree with shaggy, kind of cinnamon-colored bark.

And so all of the decades that I’ve been here, every year regularly I see a brown creeper, the bird. And you actually have a beautiful illustration of the brown creeper on some bark on the back of the book. And if not for that bark, I wouldn’t see that bird, who loves to investigate [laughter]. And they have a relationship, right? I mean…

Jim: Oh, yes. So the brown creepers climb up the trunk of trees and the nuthatches climb down the trunks of trees. You probably have nuthatches on the same tree.

Margaret: I do. And I call it the two-lane highway. Yes. Yeah. One going up, one going.

Jim: [Laughter.] Right.

Margaret: Yeah. And what are they doing? I mean, there’s birds that look, there’s also birds that stash things, cache things, in bark. But what are they doing? I mean, what’s going on there and does it serve the tree as well, or what’s going on?

“Teaming With Microbes.”

Margaret: Oh, yes.

Jim: You probably know it.

Margaret: Jeff Lowenfels.

Jim: By Jeff Lowenfels. And yeah, it’s that “no one has ever had to fertilize an old-growth forest.” You don’t have to add fertilizer because these little decomposers and recyclers are liberating the nutrients. And then they’re also producing the humus that holds these nutrients in place, and gives the soil this wonderful spongy texture, a structure that it would not have if it weren’t for the humus. And not only are they liberating these minerals, but they’re actually mixing the mineral particles of the soil with the organic parts of the soil.

Margaret: So I have a very different relationship in recent decades than I did when I was a beginning gardener with dead and dying trees. We used to sort of erase them from the landscape: “Oh, I’ve got to get that out of here,” right down to the stump grinder or whatever. And now I really revere them, and I first make them safe and make sure that nobody’s going to get harmed. But I leave them standing as snags or wildlife trees as long as possible and so forth. And then hopefully their carcass ends up beside where they grew. And all this biomass… So let’s just talk. I suspect you revere them, too [laugh].

Jim: Oh, yes.

Margaret: Tell us a little bit about a dead tree and why that’s an important creature, too, in the whole world.

Jim: Well, it provides a welcoming habitat for so many of these important in insects. And it provides food and habitat for brown creepers that love to go navigate its bark.

And it’s adding nutrients. As it decays, it’s returning minerals that were borrowed during the tree’s lifetime to the soil so they can be used by other trees, other plants. Very important.

A person that I met a couple years ago, Nancy Lawson, who writes a column for “All Animals” magazine [published by the Humane Society of the United States] called The Humane Gardener, recently wrote a book entitled, “The Humane Gardener,” in which she points out the importance of leaving these welcoming habitats for all these creatures that we should welcome. The insects, many of them are predators and parasites which help control pests in our garden. So if you have a vegetable garden or flower garden, you want to have habitat for these other creatures as well, so that they can help control whatever plant-eating insects come to your vegetable or flower garden.

Margaret: Right. Nothing is separate. Nothing is separate from anything else.

Jim: We’re all intertwined.

Margaret: Well, Jim Nardi, the book is “The Hidden Company That Trees Keep.” And the illustrations are beyond charming and it’s just so packed with information. So thank you very much, and thanks for making time today.

(All illustrations by James Nardi from his book; used with permission.)

enter to win jim nardi’s book

I’LL BUY A COPY of “The Hidden Company That Trees Keep” by James Nardi for one lucky reader. All you have to do to enter is answer this question in the comments box below:

Is there a particular interaction between a tree in your garden and an insect, bird or other animal that you’ve noticed and want to share?

No answer, or feeling shy? Just say something like “count me in” and I will, but a reply is even better. I’ll pick a random winner after entries close at midnight Tuesday, March 21, 2023. Good luck to all.

(Disclosure: As an Amazon Associate I earn from qualifying purchases.)

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 14th year in March 2023. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the March 13, 2023 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).

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