Learn your chops, learn your charts. Then throw them both away.
—Instruction to a young saxophone player
To study how trees grow is to admire not only their persistence but their imagination. Live wood just won’t quit. Every time you knock it down, it comes back again, but when a plant sprouts back, it is not a random shot, like some finger simply raised to make a point. Rather, the growing tip of any stem—what botanists call the meristem—answers with an inborn, complex pattern, like a musical tune. Something had knocked the top off a London plane tree in Brooklyn. It had already been forty feet tall. It hadn’t just sprouted a new arrow-upright stem. The sprouts at the broken edge had ramified into a set of eight complete little plane trees, each one closely resembling what its parent had looked like twenty years before, a bouquet atop the trunk.
In a grove of ancient junipers beside a village in the Spanish province of Castile, one trunk had cracked and bent until it ran horizontal, parallel to the ground. All along the trunk had sprung a linear grove of new young junipers, each with the same ancestral shape.
A little branch had broken off a willow and fallen into a stream. Where it had fetched up at an eddying edge farther downstream, it had rooted, sprouted, and up had come a new tree, whose structure had been just like its parent’s.
Charlie Parker is supposed to have given the above advice to a young saxophone player. First, you had to learn your instrument. Next, you had to learn to play the tunes. Finally, you were free to improvise, to play jazz. John Coltrane’s “My Favorite Things” is a terrific example of what he meant. It begins with a perfectly clean statement of the tune, beautiful in itself for the richness of its tone, notes that are almost solid, so you could build a house of out of them. Within three minutes, the tune has modulated into completely unexpected shapes, sizes, rising and falling glissades, stops and starts, pianissimos to fortes, but it never loses the thread of that original tune. Every tree is a jazz player, in just this way, although where a long Coltrane piece might last a quarter of an hour, a tree’s performance may go on for half a millennium or more.
The tropical botanists Francis Hallé and Roelof Oldeman were the first to articulate the idea that every plant first grows to fill a form—that is, to play its tune. It does not matter whether it is a weed by the wall or a giant sequoia, whether it is a tropical Terminalia or a subarctic birch. They, along with P. B. Tomlinson, in their 1978 book Tropical Trees and Forests, wrote that every species of the higher plants can grow in only one of twenty-three different patterns. (They have since added one more.) In fact, they noticed, a few modulate from one pattern to another, and a few more seem to grow in a hybrid pattern, but all conform to the same morphology that their ancestors had.
The tree’s “chops” are inborn, a part of its inheritance. It knows how to grow in the way its parents did. The seed contains the knowledge. To learn its “charts,” the plant grows to elaborate this knowledge into its basic shape. This first statement of its tune may take a few weeks for the weed or twenty years for the oak or may last a lifetime for a fir, but in physiological time, it is just the same. All seek to fill out the pattern of stem, lateral, flower, and fruit that was handed down to it by its forebears.
Twenty-four architectural models of trees.
What are its notes, its scales, its sharps, its flats, and its time signatures? According to the three botanists, every plant plays upon six choices:
The First—To branch or not to branch. Palms, for example, never branch, though some clustering palms make the second choice, below.
The Second—If you branch, do you do so only at the bottom, or all along a stem? Bamboo, for example, is simply a colony of stems, each repeating from the base, and the small grove is in fact a single plant. Quaking aspen seems the same, but each of its new sprouts itself branches all up and down the stem. Shrubs, likewise, in general prefer the mode of living that sprouts again and again from the base.
The Third—Do your trunk and branches grow without a rest, or is there a dormant season? Most trees in the temperate zone choose the latter gambit. Trees with a definite dormant season—like spruce and fir—tend to have a very clean and open habit of growth.
The Fourth—Do all of your branches want to grow upward, all outward, or do some want to grow upward and others outward? Pagoda dogwood prefers to grow mainly outward. Staghorn sumac wants to grow mainly upward. On upward-growing, or orthotropic, stems, the leaves and twigs tend to be organized symmetrically around the stem, in spirals of opposite pairs. On outward-growing, or plagiotropic, branches, the leaves and twigs appear in flattened planes along the edges of the branch, like a phalanx of wings.
The Fifth—Do you flower at the branch tips, or on smaller lateral branches? Again, sumac flowers at the terminals, so each year’s new growth must start from dormant laterals below the tips. It makes what look like buck’s horns, hence the common name “staghorn sumac.” (In one species, the sprouts even have the velvet of young horns.) If you flower on laterals—like most temperate zone trees, such as maples and ash—you can continue to grow more or less straight upward while your branches go straight outward, and if any difficulties occur, one growing tip can substitute for another.
The Sixth—Do your branches change back and forth between growing outward and growing upward? This is a flexible arrangement that lets a plant fill the space above and around it. Frequent changes of upward-growing top branches allow it to exploit more sun to one side or the other. Hemlock is one example. It is wonderful to see how, for all of its ability to reach eighty and more feet in height, it has a nodding top that easily trades off its leading upright branch. On average, the leader changes seven times in ten years. The top of a hemlock is a juggler.
Out of these six choices each plant plays its tune, the phrase that has characterized its kind for millions of years. No matter where its seed sprouts, each will try to play its melody. Many of the twenty-three-plus possible tunes are played only in the tropics, where abundant water and little cold let plant imaginations run wild. In the temperate zone, where winter is winter and where inundation may be followed by drought, fewer and more flexible tunes are the rule. The three botanists named all of the models in honor of other botanists who had studied the trees that exemplify that form. Rauh’s model is the most common among temperate trees. Here, the trunk and branches are functionally equivalent, so if necessary one can become the other. It flowers on lateral branches, not tips, so it does not need to bifurcate to go on growing. It rests in winter and leafs again in spring. Troll’s model is the next most common. Here again, the flowers are lateral, and the plants take a rest in dormancy. The plants are never merely a single trunk or assembly of trunks. Their branches waffle: when they begin life, they want to grow out, not up, but at the end of the season their tips turn upward. Here is a tune with a phrase that stretches out all year, only to run up the scale at the end, but again, as in Rauh, the effect is to let the plant expand both out and up. A third common model in the temperate zone is Massart’s, although it is a relic of an older world. Spruces, firs, and many of the conifers play this tune. Their trunks are upright, but their branches only want to grow outward. Because they rest in winter, they tend to have a very neat and consistent growth habit, both upward and outward. They grow both up and out in what look like whorls.
When conifers ruled the world, in the warm and equable time before the ice, they had little need of improvisation. Massart’s conical model is well adapted to capturing light, and it holds its neighbor at arm’s length. Even on mountaintops at tree line, the balsam fir simply loses its tops to the wind, but its long-reaching plagiotropic branches spread out in a carpet over the ground.
Leafy trees never had it that good. They began to spread through the evolving continents as the weather started turning nastier, around 150 million years ago. Not only that, but the damn conifers had already taken over almost every place worth living. The flowering plants, dominant today, were then marginal, sneaky, eking out a living along streamsides, on rock ledges, any place where light could get in and where a conifer couldn’t make it. From the beginning, they specialized in not specializing. Not only did they not grow in such a regular shape, they also took whatever shape they had made and reiterated it throughout their lives. Perversely, the leafy trees often started with competing branches, letting them fight it out on their way to sky, so that if one perished, another might make its way higher and wider.
Most of us, even those of us who take care of trees, have a vague notion that there are different ways of growing. Yes, an oak or an ash or a maple look qualitatively different from a catalpa or an ailanthus or a horse chestnut, from a honey locust, a beech, or an elm. But just how, we can seldom say anymore, though our ancestors almost certainly could have told us quite certainly what the difference was. They lived constantly among the trees, and their lives depended upon how those trees grew.
Still, a few species stand out. Staghorn sumac races along the edge of difficult disturbed sites much as the first leafy plants must have done during the early and middle Cretaceous period. It loves the loaf-shaped substrate upon which superhighways perch. Spreading clonally—that is, by means of an aggressive underground root system—it occupies more and more of the exposed soil of the raised berms. Often, it is in a race with quaking aspen, another clonal spreader. There is a spot near One-onta, New York, on Interstate 88 where the two spread so quickly, you can almost see them charging into each other like linemen trying to open a hole for the back. Who gets there first tends to get to stay there, and the slopes are a great place to catch the light they need to grow.
The pair are like Laurel and Hardy. Each aspen is straight, skinny, and gray. They stand close together like a room full of partygoers. Each sumac is beyond paunchy. It is downright fat and squat. A flower blooms always at the end of a new stem, so that end will never grow again. Two lateral buds beneath the flower sprout instead, and they grow out in wide open arcs like two hands raised to signal a touchdown. Next year, those two branches flower, so the same thing happens all over again. The plants less climb into the sky than they reach out to capture as much aerial real estate as they can. Two by two by two by two, each trunk ramifies into an impossibly complicated candelabra.
Most of the models make ways to mix the tall and the broad. Many of the trees in the temperate forest—the oak, the ash, the maple, the pine—grow straight up with lateral branches that also arch upward. All have spiral or opposite twigs, leaves, and flowers. The form is marvelously supple. If the top stem fails, the next lateral down turns upward to take over the leader position. Any branch can take the place of any other. If you are looking for opportunity in the dense forest, this is a fine model to follow.
Trees of equal or even greater size—the elms, the beech, the honey locust—instead grow only spreading branches. They get taller only because one new sideways branch sprouts atop the previous one, and so on sometimes to heights of more than one hundred feet. They get a little additional upward boost because in the dormant season of their first year, the new floppy branch may slightly straighten up. A quarter of all temperate forest trees grow this way. It is even more flexible than the upright model, since the sideways branches can stretch in any direction to find light, staying short if light is scarce or stretching out forty feet to reach a hole in the forest canopy. So a tree of this kind can go upward or outward as conditions change. These are the trees that make great vase-shaped canopies, so that a double row of elms or even of honey locusts above a roadway shuts out the sky above.
Still others play a tune that sends up each year a trio or more of fresh stems, all fighting one another for the light. Ailanthus trees do this, as do catalpas and horse chestnuts. Of the three or more fresh upright stems, one dominates and the others bend off sideways. As these are often lovely flowering trees, at the right time of year the tree looks like a fireworks display, with explosions of leaf and flowers at each elevation, measuring back to when the tree was small. They seem to thrive on complication.
If every tree seeks to express its model, why then does the world of plants not resemble immense phalanxes of similar shapes? Why is a forest not an array like the bottles of different brands of seltzer on the supermarket shelf?
Because of the many accidents.
Because of the uncertain world.
Because of heat and cold, storm and wind, pests and diseases.
Because of neighbors, those that are rooted, and others that are two, four, six, and eight legged.
Because of opportune openings to the sun.
Because of the subsequent improvisation.
Reiteration is the wonderful name that Oldeman gave the tree’s ability to respond to the world around it by in whole or in part replaying its melody, but in very different contexts at ever different scales. It is jazz: take the tune, stretch it, cut it into pieces, put them back together, transpose it up or down, flatten it out, or shoot it at the sky. Each tree gets its chops, gets its charts, and then throws them away. It knows the chart by heart, and so can repeat it with a thousand variations for hundreds of years, as it grows to its full stature, lives among its peers, and grows back down to the ground. Positive and negative morphogenesis, they dubbed the cycle: growing up and growing down.
As soon as the tune is played, the initial reiteration is the first major branch. As a leafy tree grows, it will generate what arborists call scaffold branches. These are the few—maybe five to eight—very large stems upon which the tree will hang most of its crown—that is, most of its smaller branches and their millions of leaves. As horticulturalist Liberty Hyde Bailey saw as far back as 1908, “A tree is essentially a collection or a colony of individual parts. . . . Branches are not so much organs as competing individuals.” The skill of the tree as an organism is like Coltrane in his vamping: it brings the variations back to the persisting theme.
Atop these scaffold branches—big, thick, and arching—come a series of smaller reiterated steps at the scale of trees, as though they were dogwoods or cherries, filling up what will be the middle story of the mature tree. Next are reiterations at the scale of a shrub, bushing out the leafy twigs to all sides where life-giving sun is to be found. Finally, when the tree is about to achieve its full size, the repetitions are practically the size of herbaceous plants. Each new sprout complex extends only a foot or two from the parent branch. All the new branchlets will remain forever small in diameter. The tropical botanists call this last layer the Monkeys’ Lawn.
The first third of the tree’s life is positive morphogenesis. “Building up” is what it means. The phase may last one hundred years. Then, for another century or two, the tree may maintain its full stature, no longer able to grow much taller or wider, but still replacing every lost piece of the Monkeys’ Lawn or the shrub layer with fresh improvisations. Finally, it enters on the third stage of its life, negative morphogenesis, or “growing down.” An old saying about oak trees put it succinctly: “Three hundred years growing, three hundred years living, three hundred years dying.”
Growing down is not just decay. It is as active and improvisational as was the building up. Roots are damaged or die. Branches are lost to storms. Hollows open up on the trunk and are colonized by fungi like the wonderful and aptly named Dryad’s Saddle. The tree’s solid circulation system resolves itself back into discrete pathways, some living and some dead. It becomes obvious that scaffold branches were once separate trees, as they become so again, some maintaining their root systems and others losing them. Now the tips of the higher branches begin to die back. Instead of growing new reiteration branchlets on their undersides, as they did in their youth, they now sprout perfect little trees of their species on the tops of the branches, between the trunk and the dead tips. It is a complete restatement of the thematic tune, happening dozens of times among the still living branches.
Now that we know trees can spend a third of their lives in this process, arborists are no longer so eager to remove a tree once symptoms of age set in. By studying and keeping up with the plant’s own process of growing down, the pruner can keep the tree safe and lovely for many years longer than was once thought possible. People have determinate life spans. Trees do not. Although the trunk and branches are old and decaying, the creature is still producing the brand-new babies of the reiterated stems. An ancient tree is thus a mixture of newborns and Methuselah. By helping it to retrench, we can keep it for longer.
Little by little, a tree loses its crown, first small branches, then larger ones. Roots decay. The circulation system that carries water aloft to the leaves starts to break down. When no leaves emerge on a branch, it can no longer feed itself. It dies and falls to the ground, but the tree does not give up. When a giant that was once ninety feet tall has shrunk to a height of twenty feet, little images of itself may sprout from the lower trunk or even from the root flare, wherever a living connection between root and branch survives. I once saw an ash on the Somerset Levels that had left just a single sprout on the trunk and one from just above the roots. All the rest of the trunk was dead and its base stood in a posture that looked like a dancer’s plié. It is not impossible that one or the other of those last sprouts—if only they can generate their own stable root systems—may grow once again to ninety feet tall. Phoenix regeneration is the name for this process. Potentially, every tree is immortal.
The fine British arborist Neville Fay outlined the seven ways that this regeneration can happen: One of the reiterations at the base of the trunk can make its own root system and its own new trunk, as the ash I saw on the Levels was doing. An old scaffold branch can do the same. Or the tree may completely resprout from the basal root system, rising again from the ground up. Or the tree’s lowest branches may strike the ground, root where they hit, and generate a new tree. Or a small diameter trunk can form right inside the decaying ancient one and there make a fresh start. Or new roots may start in the hollow at the base of the tree, and touching ground, they may generate a new trunk and crown. Finally, the tree may fall right over, its lateral branches turning into new trees.
I had a client on the eastern shore of Maryland. Their house was bowered in a forest garden. They owned hundred-foot oaks, huge pecans, beautiful Chinese chestnuts, mature southern magnolias, a unique double allée of gigantic deodar cedars, but the very best of their trees was a fallen Osage orange. By most accounts, it is not a high-value species. Michael Dirr, whose Manual of Woody Landscape Plants is the standard reference for park and garden trees, commented, “Not worth recommending for the residential landscape.” It drops fruit like corrugated puke green cannonballs, and the wood is so hard that to hand-saw through a dead trunk can wear out two grown men. Indeed, my clients showed the tree to me sheepishly. We rounded a corner of their house, admiring a huge pin oak in the distance, and there in the foreground was the fallen tree.
Incipient phoenix regeneration of an ash on the Somerset Levels.
I stopped, and I believe my mouth must have fallen open.
“What do you think of it?” asked the wife, wrinkling her brow. I could see she was mentally gritting her teeth against what I was about to say.
“Amazing!” I replied.
Their brows both unfurrowed. A smile broadened on her face, but she wanted to make sure.
“You like it?” she asked.
“It is extraordinary,” I answered. “The best of all your trees.”
“Oh, what a relief,” she breathed. “We were told we should remove it.”
I expressed shocked disbelief. I think I may have thrown up my hands and pretended to tear my hair.
There on the ground before us was a trunk about forty feet long and about three feet in girth. It had fallen over so many years ago that ferns, mosses, and small herbaceous plants had colonized the root plate that stood at one end taller than a tall man. Because it was an Osage orange, however—renowned for its resistance to decay—the entire length of the trunk was otherwise intact. At the opposite end was the wonder.
Once they had been branches on the trunk, but when the tree had fallen, the former branches had changed their minds. The original crown of the tree had died away. All the other branches had died, but these two had risen straight into the air, as though they were and had the perfect right to be new young Osage orange trees. Decades later, each of them was forty feet tall. One was evidently still depending upon the remaining roots in the ground on the bottom of the root plate. The other had also begun to put down its own root system, snaking over the dead trunk and into the ground.
It is as though a person rested her arm on the dirt, spread out her palm, and two perfect new arms emerged from her life line, complete with all the muscles and tendons and circulation, the hands, palms, fingers, and fingernails. Or perhaps more accurate, as though a person lay down at night and had two new people overnight sprout from his torso, complete from toenails to cowlicks. I think John Coltrane would have loved phoenix regeneration. It is like those moments in “My Favorite Things” where the whole piece seems about to jump off the top end of the soprano sax register, but suddenly the tune takes up again.
We think we know a tree when we can name its genus and species, perhaps place it in a family, and recount the tale of invisible processes like photosynthesis and the production of pigments. What if this were really a strange, abstract, and less useful way of knowing trees than to know them by the forms in which they grow, live, and die? Up until the Neolithic and probably even into the Middle Ages, human beings were better at the latter than the former way. In those times too, they had a very active relationship to trees, depending on them for energy, warmth, structure. (Nowadays, we think we have graduated to oil, but that is only a way of robbing the energy of ancient trees.) In those days, we knew trees the way we know friends: what they like and don’t like, how they are likely to respond to a thing we do with them, what we should under no circumstances try with them. Each exchanged with the other. There is no call to think people had to be altruists to do this. Rather, they knew what was good for them better than we do.