One Tough Tree

(Or, How I Got Siberian Elm Disease)

By Gordon Grice and Shelby Lee Adams
Sep 1, 2001 5:00 AMNov 12, 2019 4:39 AM


Sign up for our email newsletter for the latest science news

Some summers ago I stood precariously on a 6-foot stepladder, sawing off the limb of a Siberian elm. The handsaw bit through the textured bark in a few smooth strokes, then hit the heartwood and slowed. I tried not to rush. I thought I would actually go faster by keeping my strokes smooth and long, conserving the strength of my arm.

The author's wounded but enduring tree. Siberian elms grow in sunlight or shade, in dry sand or riverbank mud. The only forces that seem to do them real harm are fire, ice, lightning, and devastating winds.

My eyes wandered. Siberian elm bark is so deeply textured, so rich in convolutions, that it has always suggested faces to me. The curve that would complete one face is absent, and instead some broad ridge sweeps in and draws my eye farther, to a face appended to the first, and this second is incomplete and verges prematurely into two others.

If I let myself simply gaze at the bark, I wander from face to face until I catch myself losing everything, following lines without attaching meaning to them, only vague intimations, moods. But this time something stopped me and made my eyes shift their focus.

It was a cockroach, a thin brunet one, and he was acting strangely. He was close enough to feel my breath, but he didn't run away. I stared at him until I noticed a deficiency: His antennae, which should have been long and whip-thin, were blunt stubs. I flashed to something I had once read, about the habits of a certain predatory wasp. The wasp bites a roach's antennae off, rendering the roach senseless and unusually docile. The wasp can then do with her victim what she will.

As I remembered this, a wasp crawled into view, moving at a businesslike clip. She was leaner than a honeybee, half black and half red. She seized the roach by the stubs of his antennae and led him through the valleys of bark. After about 6 inches, she let go of the roach and left. She'd be back.

I knew from watching similar behavior in other species that this wasp was about to lay an egg on the cockroach, who would stand around waiting to become a smorgasbord for her larva. The special delight of such arrangements is that the prey stays alive through most of it. Otherwise, he would rot and be useless as wasp food. The wasp clan has diversified enormously, so that it can parasitize and prey on many sorts of living things— trees and tarantulas, caterpillars and beetles. Some wasps parasitize other parasitic wasps, and these hyperparasites in turn are parasitized by other wasps, and these by others. Perhaps this hyperparasitic regression goes further, but it's hard to say: At that point, the wasps are too small to be seen without a microscope.

The wasp returned. She was on foot the entire time, never flying. Each time she came back, she would lead the roach along the bark a few more inches. I couldn't see the other end of her round trip, the place she had chosen for him. She led the senseless roach around the trunk and out of my sight. I climbed after them a little way, but some idiot had been sawing at the branches, leaving little to climb on. I strained my eyes gazing at that infinity of folded faces, which I now realized was also a vast graveyard and nursery.

I suppose I should mention why I was sawing limbs off the tree: I hated it and wanted it dead. My doctor had recently told me I was allergic to elms, but I'd known that earlier. Each spring I would notice the sudden buds on the elm twigs, bulging like blood blisters. On a morning soon after that I would wake sneezing, and that would prove to be the morning the buds had opened into tiny burgundy flowers. They were odd, gritty flowers that seemed to erupt rather than bloom. A few days later I would find my windshield clotted with specks of a substance indistinguishable in color and viscosity from Super Glue. This stuff is the waste aphids excrete after attacking elms. Such attacks rarely do the elms any lasting damage.

My doctor's formal pronouncement roused me to action. How stupid it is, I thought, that a person who suffers from the floating poison of the elm should allow a specimen to exist in his own yard. I remembered that elm roots clog sewers. I remembered the pale disks of elm fruit that blew in under the door every May, which resisted the broom and the vacuum with annoying tenacity. I further reflected on the dismal scratching sound that sometimes woke me on windy winter nights— the reaching branches of the elm, grasping at the furnace vent on the roof. Every summer I pruned those limbs far back; every winter they scratched to prove they had reached the house again.

I resolved to kill the thing or at least prune it so far back that winter would finish it for me. I went at it with a telescoping pruner and a ladder and a handsaw. The early work went well; I took off a branch or two every evening, and the patch of lawn where the grass would never grow was suddenly flooded with light. The scratching on the roof stopped. The gray-brown bark yellowed with oozing sap beneath the wounds I made.

And while I inflicted this gradual violence on my enemy, I began to fall in love with it. I was discovering an ecosystem new to me, one that had existed just over my head all my life. The roach-capturing wasp was only my first discovery in this new world. Another day I came upon a baseball-sized gray nodule. I assumed it to be merely an aberrant growth in the wood, but when I tried to steady myself against it, it bubbled beneath my hand, and the air was suddenly full of a smell reminiscent of bad banana and distant skunk. It was a mass of squash bugs, the shield-shaped, thumbnail-sized gargoyles I encountered in great profusion in my garden every summer. I had always wondered where that foul-smelling congregation went between attacks on my garden. Here they were, camouflaged in the shelter of the elm's bark.

I found the black-and-yellow larvae of the elm leaf beetle, recognizable because their colors matched the adults' own. I had seen the adults often enough— they reigned for a week or so every summer, through profusion rather than might. About the size and shape of a sunflower nutmeat, an elm leaf beetle is a feeble creature in my experience, breaking at any touch. I found them clotted beneath the windshield wipers on my car, or orbiting the porch light, or littering the skeins of the garden spiders that rest by day in a patch of marigolds beneath my kitchen window. Some nights I saw the spiders cutting the elm leaf beetles loose uneaten, as if such food were bad for their cholesterol.

The larvae were more sinister than the adult beetles, though no more durable. I would sometimes kill them with an accidental touch, their yellow excretions staining my hands. But the damage they did to the elm was astounding: Its green curtains of leaves became lacy in the space of three days. Even when I climbed the ladder to search, it was hard to find an unmolested leaf. Some leaves had been drilled with a few round holes. Others had been worked along the side, their normally serrated edges chewed into a different pattern of serration, the notches of which matched the span of a larva's mouthparts. Still other leaves had been reduced to their pliant green spines.

The astounding aspect of this insect assault is how little it actually harmed its victim. The tree in my backyard transformed itself in another few days, tossing its tattered leaves to the ground and erupting with the folded beginnings of new ones.

As my pruning project expanded to fill weeks and then months— I admit I skipped an evening here and a month there— my admiration for the Siberian elm grew. The aphids had hardly slowed it; the elm leaf beetles had proved only a minor inconvenience; my own mutilations had inspired the tree to do a hydra routine, putting out at least two leaf-laden twigs at the rim of every oozing wound I made. This toughness explains why a tree murderer from the Oklahoma Panhandle should find himself pondering a plant from Siberia.

The Panhandle is notorious for its weather: late freezes; Indian summers that fool plants into suicidal early bloomings; fluctuating humidity; temperatures diving 40 or 50 degrees Fahrenheit in a few hours; drought; an occasional tornado. One spring a single storm deposited 4 feet of hail on the highway but knocked only two old branches and a little greenery off my elm. The climate is inhospitable to many plants that do well elsewhere. That's why people around here brought in a shade tree from a place with even tougher weather: Siberia. My forebears promptly named the tree the Chinese elm, probably on the theory that all exotic locales to the east may as well be China. Confusingly, another tree really is called the Chinese elm, but its flat bark, which flakes off in leprous patches, is nothing like the furrowed geography of the Siberian species.

Several of the 30-odd species of elm expanded their ranges in the 1930s. The Oklahoma Panhandle, poster child for the Dust Bowl, needed rows of trees to counter erosion, and the hardy Siberian elm was the tree of choice. The reason the Siberian succeeded where other trees, even other elms, failed was its aggressive root system. When much of the topsoil is literally in the air, only a plant that can drill its own well has a chance.

My own Siberian elm was already in leaf one April when a late blizzard dropped the temperature into the single digits for two nights. The freeze seemed to demolish every bit of green on the tree. Afterward, the melting snow was filthy with a dust made of brittle bits of elm leaf. But a few days after this apocalypse, the tree was leafing out again. By summer it looked as hardy as it ever had.

I shouldn't give the impression that the Siberian elm is impervious to harm. Dutch elm disease and other fungal infections attack the species, and so do a broad range of bacteria, nematode worms, viruses, and even mycoplasms. The cemetery in my hometown is called Elmhurst. It is full of Siberian elms more than half a century old. Some are healthy. Others bear goiters the size of human heads. The bark on these diseased excrescences snaps off easily in my hand. The naked wood beneath seems made of thick liquid movements now frozen, like the pattern on the surface of hardened fudge. Tiny spikes of wood protrude here and there. Such deformities remind me of the Elephant Man. But these trees have been alive in this condition, putting out new growth each spring, for a decade.

The tree in my backyard eventually beat me. I pruned its limbs as far up as I could reach, and still it thrived. The cement walk was littered with disks of elm fruit, cast like coins to a beggar. At the foot of the tree's trunk stood a new sapling, sprung from old roots. In a corner of the yard was an amputated limb, as long as I was and thicker than my thigh. Since I had cut it down, its flanks had unfolded a dozen slender sprouts, each now tatted with tender green.

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 40% off the cover price when you subscribe to Discover magazine.

Copyright © 2024 Kalmbach Media Co.