REVIEW: How to Read a Tree, by Tristan Gooley

How to Read a Tree: Clues and Patterns from Bark to Leaves, Tristan Gooley (The Experiment, 2023).

Okay, I admit it: I read this book because I wanted to know more about the trees in my yard.

I’m afraid that’s not how Tristan Gooley means it to be used. He’s an expert in what he terms “natural navigation,” which means finding your way wherever you’re going using the sun, moon, stars, weather, land, sea, plants and animals. He teaches classes in it. He tested Viking navigation methods in a small boat in the north Atlantic and wrote a scholarly paper about it. He traveled the desert with the Tuareg. He’s the only living person to have crossed the Atlantic solo in both a plane and a sailboat.¹ Meanwhile, I consistently walk a block in the wrong direction when I come out of the subway. But I am interested in trees!

Do you think much about trees? Could you draw one from memory and come up with something besides a fat green lollipop? Can you describe a tree you walk past every day with something more than its species and “leaves turn a pretty color in the fall” or “had its whole middle chopped out because planting trees directly under power lines is a terrible idea”? (Or if you live somewhere urban enough to have buried power lines, “they really, really should have made sure all these ginkgos were male.”)² My guess is that you can’t, because most of us couldn’t, but trees deserve some real thought. They are actually fabulously, unintuitively weird, and learning just a little bit about how they work will dramatically enhance your ability to understand why the world around you is the way it is. I don’t expect I’ll use a tree to find my way any time soon, but since reading the book I’ve started spotting things in my yard and my neighborhood that I’d never noticed before — and noticing things is halfway to understanding them. (Which is, of course, why you must not be permitted to notice that which you are not supposed to understand.)

The most fundamental insight here is that trees are not like animals. This sounds breathtakingly obvious (and indeed, when I shared this pearl of wisdom at the dinner table everyone laughed at me), but it’s hard to internalize. Our increasingly urbanized and domesticated lives have so impoverished our natural imaginary — the available stock of symbols, metaphors, and archetypes through which we understand the natural world — that we’re more or less limited to commensals and charismatic megafauna, and are therefore vaguely surprised when we encounter organisms that work differently.³ And trees really do work differently, in a wide variety of ways that make perfect sense when Gooley points them out.

What are these differences? Well, for one thing, where animals have their physical architecture written into their genes, trees — like all plants — have potential. Sure, they have general growth habits⁴ (you’d never mistake a willow for a maple), but compare two trees of the same species — even two genetically identical trees cloned from grafts or cuttings of the same parent — and you’ll find dramatic structural differences depending on how the individual tree grew. This isn’t true for animals: one lion might be smaller than another, or bear the scars of an old injury, but all lions have four legs with the same joint anatomy. A lion will never grow a new leg, drop an old one, or add new tendons to support a particularly overworked limb. Trees, on the other hand, do all of those and more, following general rules dictated by species but growing in response to the conditions they encounter. And because only the top of the tree continues to grow up — a branch five feet off the ground will still be five feet off the ground in a decade, though quite a lot thicker — you can read a tree’s whole history in its structure. As with looking at a genome, looking at a tree is a way of looking into the past.

Trees seek the light. Just down the street, my neighbor’s entire front yard is shaded by three enormous oak trees planted in a rough triangle and each arching gently away from the others (with a surprising similarity to the Air Force Memorial) as they try to escape each others’ shade. A few blocks away is a survivor of a similar situation, an old pine tree that’s branchless most of the way up its trunk so you can really see the alarming 15° lean with which it grew. Some long-gone giant cast the shade that sculpted this tree into its present funny shape, and if we were in the woods we might be able to see its stump — Gooley encourages the reader to greet a woodland stump by looking for the “footprint” of the missing tree in its surroundings — but I suspect this one was probably removed to make way for the foundation of the nearby house. (Given the apparent age of the pine and the house, its old neighbor probably met its end around the time the new streetcars turned this farming village on a railroad into a proper suburb.)

But light-seeking explains much more than gross structure. When I was a kid, my neighbors and I used to hide inside the massive spruce tree on their lawn, where the needles vanished and there was a great conical hollow with only scratchy bare branches for us to avoid. Broadleaf trees do something similar: look carefully and you’ll find that near the trunk it’s mostly just bare branch, with the leaves concentrated near the “surface” of the canopy. This makes perfect sense, after all, because leaves take energy to grow; there’s no point in having them anywhere they won’t capture enough light to pay back the tree’s investment. For the same reason, freestanding trees (like you’ll often find in parks or built-up areas) tend to be bushier than the same species in a forest, because obliging human landscapers keep removing the other trees that might compete with them for the light.

If you’ve ever seen a branch or trunk with only its outer bark removed, as in driftwood, you might have noticed that the smooth wood underneath seems to be speckled with tiny pimples. Those are the dormant “epicormic buds,” which spend their lives waiting patiently under the bark to spring into action when circumstances call for them to become a branch. The precise signals involved depend on the location, but one very important signal is the amount of light a bud receives: recently my oak tree lost a high-up branch to a storm, and now one of the large structural branches that had been shaded “inside” the canopy is bristling with leafy twigs. But they won’t all make it to full branch status, because trees are ruthless self-pruners: when a branch is no longer bringing in more energy than it consumes — whether because the tree has gotten so tall that the branch is now in shade, or because it’s one of many twigs competing for the new light — the tree simply shuts it down. The junction with the trunk (or larger branch) is sealed off with resins or gums, cutting off the branch’s access to water and nutrients, and it quickly dies and either rots away or, newly-brittle, is blown down by a storm.

Trees govern their growth with complex hormonal signals produced in response to those biochemical sensors attuned to light and gravity. Unfortunately for me, because I think this stuff is very interesting, Gooley doesn’t spend much time explaining how all this works;⁵ he’s mostly interested in using trees as a tool for natural navigation, so he gives only enough explanation of how trees work to contextualize the observable patterns that help us to orient ourselves. Self-pruning, for example, comes up because trees will grow more branches on their sunnier side (the south, in the Northern Hemisphere) and so will inevitably prune more branches on that side. Thus, you can tell the direction by finding which side of a tree has more of the circular self-pruning scars. Or more mnemonically: “Trees have eyes on their southern sides.” Unfortunately many of his patterns are less useful in built-up areas — in the wild, spotting a willow, an oak, or a pine will tell you something about the local climate and soil; in the suburbs, it will tell you something about the landscaping preferences of whoever owned the house fifty years ago — but in this particular case I’m sure with a little practice you could learn to differentiate between a self-pruning scar and a “please stop clogging my gutter with leaves four times every fall” tree surgery scar.⁶

Still, with a little thoughtful application, his rules can still explain a great many of the interactions between trees and our built environment. Take, for instance, the urban “street tree”:⁷ obviously it ought not to drop stinky fruit and should be appropriately sized for the space, with roots that tolerate restriction to the smallish area urban planners can spare but that go deep enough not to make the sidewalk buckle (maples are right out). But beyond that it must tolerate salt and pollution — and people walking over its roots, because the soil compaction from repeated footfalls or car traffic is fatal for the roots of many species. (On my walk to the library, I pass two different trees with large dead spots in their canopies — both of which are exactly where the trees overhang parking lots and the weight of the cars is slowly killing the roots beneath.) Or think of all those slumbering buds: they’re particularly prevalent at the bottom of the trunk, just above the root flare, and it’s this prevalence that humans take advantage of when we coppice. Some woody plants⁸ send up these sprouts with great frequency, a habit that makes them very useful for growing livestock- or passerby-proof hedges,⁹ but most trees will only sprout so low down their trunks when the trunk and branches are in serious trouble. The other day I turned down a street I don’t usually visit and saw an oak with a ring of bushy twigs exploding out of its trunk about three inches off the ground, which thanks to Gooley I recognized as a sign of a tree in distress. And then I looked up and saw that the branches had all been cut inexplicably short, terminating a mere three or four out from the trunk, and understood why the tree had sent out these sprouts, its desperate Plan B.

There’s a long, proud history of using trees as a metaphor for culture or society: they last much longer than we do, they grow slowly but to impressive proportions, and in the natural course of things they’re usually very difficult to disturb right up until they fail catastrophically. But it works on another level too, because every tree you see — just like every culture — is the result of a complex evolutionary process. And I don’t mean this in the sense that the genus Ilex evolved to tolerate heavy shade, I mean quite specifically that this particular holly tree you’re considering took its present form because it tried lots of things in response to the conditions it encountered, abandoned the ones that didn’t work, and leaned hard (perhaps literally) into the ones that did. Cultures develop norms, institutions, ceramic techniques, and other social and physical technologies the way trees develop branches: bound by certain fundamental laws of nature and by path dependency, but responding to circumstances to take any of the many forms available within the extensive possibility space.

Take, for example, reaction wood: trees grow this incredibly strong, hard wood at areas of great mechanical stress, typically where a large horizontal branch meets the trunk. It would be terribly inefficient to grow these “branch collars” at every joint, since many twigs or small branches will be self-pruned before the metabolically-expensive material actually pays off, and any given branch will have its own specific stresses, so each collar will have its own unique size and shape based on its particular circumstance. Similarly, culture accretes around real material necessities: we develop ways of interacting with each other and with the physical world when and as we need them. No thirty member hunter-gatherer band would ever develop the complex system of introduction and reputation that we see in Jane Austen’s novels, and no society bound by intensive kinship norms would bother creating impersonal market institutions — they wouldn’t need them.

But while it can be useful to inspect some tree branch or cultural norm on its own, a holistic consideration often reveals more about a large, self-reinforcing system than do sequential analyses. Consider the tree phenomenon sweetly called “inosculation” (from the Latin for kissing), in which tree trunks or branches that touch begin to grow together and share resources and burdens. For a while this can be a structural advantage, but often the mutual support means the branches never undergo enough mechanical stress to develop the supporting wood they would need in order to survive on their own; when one branch weakens or drops, the other soon follows. It shouldn’t be hard to think of analogues in the realm of culture — indeed, Joseph Henrich’s explicit argument in The WEIRDest People in the World is more or less that the institutions of pre-Christian Western Europe couldn’t sustain themselves in the absence of cousin marriage. And a common tactic of those who want to take down a whole system is to attack one particular load-bearing institution.

So say I’ve convinced you that society really is like a tree. What then? Well, among other things, it gives us a lot of new metaphors.

Curtis Yarvin

recently offered one:

There is an ancient Lithuanian proverb about a village whose central square was long shaded by a great oak tree. Late one Saturday night, a madman went mad with an axe and cut down the tree.

That night, as was his wont, the wise man of the village was deeply in his cups. When, on Sunday afternoon he painfully arose and looked out his window over the plaza, he exclaimed to see the great oak cut down—then exclaimed again to see the villagers, with rope and crane and shovel, replanting the tree.

They had dug the stump out to a pit, where they were planting the hacked-off trunk. Of course the oak’s leaves were already starting to wither. Still in his pajamas, quite careless of his pounding head and the sun’s savage glare, the wise man rushed down the stairs and into the square. He began to gather acorns and bury them in little holes. Everyone thought the wise man, too, had gone mad. Didn’t he want the tree back? What was he, a squirrel?

In this case, planting acorns is just about the only thing a person could do — obviously replanting a severed trunk is pointless, and Yarvin stipulates that the stump has been removed. But if the stump had remained, the tree would still be in business! Merely cutting down an oak doesn’t usually kill it; an oak stump is full of epicormic buds and if you give it a season or two you’ll be overwhelmed with new shoots. (Here's a photo.) Let it go a few decades and you’ll have stout trunks. (Here’s another photo.) In fact, even being blown over in a storm doesn’t reliably kill an oak: as long as a few roots stay buried, the branches and buds on the upper side will often become new trunks growing up out of the fallen log. (Here’s yet another photo.)

Now of course a metaphor is only a metaphor, and the only reason to compare society to an oak rather than a conifer (which is much less likely to survive being felled) is that Edmund Burke did it first. But the more we notice and understand about trees, the more we’re able to create these sorts of illustrative metaphors that allow us discuss our social and political worlds in new ways. So what is our present situation, anyway? Has the stump been removed? Of course it’s probably smart to plant acorns regardless, but shoots from a coppiced oak have the benefit of an extensive root system and will grow much more quickly than new seedlings — so, are the roots intact? And if only some of them, which ones? Because, after all, just because a tree survives doesn’t mean it looks the same. We should expect changes, but what sort?

I’ll leave you with one final image, which I found the most powerful of the book, and let its metaphorical import remain an exercise for the reader:

The wood at the heart of an old tree is dead and if it remains protected by the bark and outer layers, it will last a long time as a stable but lifeless part of the tree. But if a crack or other weakness allows microorganisms into the dead wood, decay begins. Many ancient trees start to rot from within but can hold onto life for centuries by keeping their outer layers in working order. The outside is also the most important part for structural strength, which is another concept we skeleton-framed creatures find counter-intuitive.

If there is trouble at the center of an old tree’s base, the tree can survive by growing out and around the trouble. Ancient trees can profit from this process by reabsorbing some of the nutrients that end up back in the soil following the decay of their own interior. (Amazingly, they also grow roots within their trunks to feed off their own decay.)

[Here’s a final photo. —JP.]

1. The late Steve Fossett did it first, but since he holds about a billion other records it feels churlish to take this from Gooley.

2. Only female gingkos drop those awful berries. There are entire all-male cultivars that make fabulous trees, and somehow, inexplicably, I spent every autumn of my childhood scraping horrible stinky mush off the bottoms of my shoes. Why.

3. Also on this front, I recommend Merlin Sheldrake’s Entangled Life, which is exactly the sort of book about fungi you would expect someone named Merlin Sheldrake to write.

4. In fact “tree” is really just a growth habit, evolved independently by thousands of unrelated species of plants, because trees are the crabs of the plant kingdom.

5. I went looking for more information about the “how” and this was the best single thing I found.

6. And yes yes, we do often also cut down dead branches because we want to prevent them from falling on cars or power lines, but in the case of self-pruning they’ll be dead because the scar has already formed; the guy with the chainsaw is just filling the role of the wind gust.

7. In case you’re wondering, the best street trees in most of America are the ginkgo (male, please) and the American sycamore or its hybrid the London plane.

8. There’s no actual “official” difference between a shrub and a tree. Both are woody plants, and while trees generally get taller and are more likely to have a single stem there are definitely multi-stemmed trees (think birch) and plenty of shrubs can be grown as single-stemmed, tree-like “standards.”

9. Technically, many hedging plants actually use “suckering,” which is sprouting from a bud on the root rather than one on the trunk.