When I examined one of my young beech trees, it turned out that a single 8-inch-long twig already had twenty-five of these swellings. I could find no other indicator of the tree’s age on its tiny trunk, which was no more than a third of an inch in diameter, but when I carefully extrapolated the age of the tree from the age of the branch, I discovered that the tree must have been at least eighty years old, maybe more. That seemed unbelievable at the time, until I continued my investigations into ancient forests. Now I know: it is absolutely normal.
Young trees are so keen on growing quickly that it would be no problem at all for them to grow about 18 inches taller per season. Unfortunately for them, their own mothers do not approve of rapid growth. They shade their offspring with their enormous crowns, and the crowns of all the mature trees close up to form a thick canopy over the forest floor. This canopy lets only 3 percent of available sunlight reach the ground and, therefore, their children’s leaves. Three percent—that’s practically nothing. With that amount of sunlight, a tree can photosynthesize just enough to keep its own body from dying. There’s nothing left to fuel a decent drive upward or even a thicker trunk. And rebellion against this strict upbringing is impossible, because there’s no energy to sustain it. Upbringing? you ask. Yes, I am indeed talking about a pedagogical method that ensures the well-being of the little ones. And I didn’t just come up with the term out of the blue—it’s been used by generations of foresters to refer to this kind of behavior.
The method used in this upbringing is light deprivation. But what purpose does this restriction serve? Don’t parents want their offspring to become independent as quickly as possible? Trees, at least, would answer this question with a resounding no, and recent science backs them up. Scientists have determined that slow growth when the tree is young is a prerequisite if a tree is to live to a ripe old age. As people, we easily lose sight of what is truly old for a tree, because modern forestry targets a maximum age of 80 to 120 years before plantation trees are cut down and turned into cash.
Under natural conditions, trees that age are no thicker than a pencil and no taller than a person. Thanks to slow growth, their inner woody cells are tiny and contain almost no air. That makes the trees flexible and resistant to breaking in storms. Even more important is their heightened resistance to fungi, which have difficulty spreading through the tough little trunks. Injuries are no big deal for such trees, either, because they can easily compartmentalize the wounds—that is to say, close them up by growing bark over them—before any decay occurs.
A good upbringing is necessary for a long life, but sometimes the patience of the young trees is sorely tested. As I mentioned in chapter 5, “Tree Lottery,” acorns and beechnuts fall at the feet of large “mother trees.” Dr. Suzanne Simard, who helped discover maternal instincts in trees, describes mother trees as dominant trees widely linked to other trees in the forest through their fungal–root connections. These trees pass their legacy on to the next generation and exert their influence in the upbringing of the youngsters.18 “My” small beech trees, which have by now been waiting for at least eighty years, are standing under mother trees that are about two hundred years old—the equivalent of forty-year-olds in human terms. The stunted trees can probably expect another two hundred years of twiddling their thumbs before it is finally their turn. The wait time is, however, made bearable. Their mothers are in contact with them through their root systems, and they pass along sugar and other nutrients. You might even say they are nursing their babies.
You can observe for yourself whether young trees are playing the waiting game or putting on a growth spurt. Take a look at the branches of a small silver fir or beech. If the tree is obviously wider than it is tall, then the young tree is in waiting mode. The light it is getting is not sufficient to create the energy it needs to grow a taller trunk, and therefore, the youngster is trying to catch the few leftover rays of sunlight as efficiently as possible. To do this, it lengthens its branches out sideways and grows special ultra-sensitive leaves or needles that are adapted to shade. Often you can’t even make out the main shoot on trees like these; they resemble flat-topped bonsai.
One day, it’s finally time. The mother tree reaches the end of her life or becomes ill. The showdown might take place during a summer storm. As torrents of rain pour down, the brittle trunk can no longer support the weight of several tons of crown, and it shatters. As the tree hits the ground, it snaps a couple of waiting seedlings. The gap that has opened up in the canopy gives the remaining members of the kindergarten the green light, and they can begin photosynthesizing to their hearts’ content. Now their metabolism gets into gear, and the trees grow sturdier leaves and needles that can withstand and metabolize bright light.
This stage lasts between one and three years. Once it is over, it’s time to get a move on. All the youngsters want to grow now, and only those that go for it and grow straight as an arrow toward the sky are still in the race. The cards are stacked against those free spirits who think they can meander right or left as the mood takes them and dawdle before they stretch upward. Overtaken by their comrades, they find themselves in the shadows once again. The difference is that it is even darker under the leaves of their cohort that has pulled ahead than it was under their mothers. The teenagers use up the greater part of what weak light remains; the stragglers give up the ghost and become humus once again.
Further dangers are lurking on the way to the top. As soon as the bright sunlight increases the rate of photosynthesis and stimulates growth, the buds of those who have shot up receive more sugar. While they were waiting in the wings, their buds were tough, bitter pills, but now they are sweet, tasty treats—at least as far as the deer are concerned. Because of this, some of the young trees fall victim to these herbivores, ensuring the deers’ survival over the coming winter, thanks to the additional calories. But as the crowd of trees is enormous, there are still plenty that keep on growing.
Wherever there is suddenly more light, flowering plants also try their luck, including honeysuckle. Using its tendrils, it makes its way up around the little trunks, always twining in a clockwise direction. By coiling itself around the trunk, it can keep up with the growth of the young tree and its flowers can bask in the sun. However, as the years progress, the coiling vine cuts into the expanding bark and slowly strangles the little tree. Now it is a question of timing: Will the canopy formed by the old trees close soon and plunge the little tree into darkness once again? If it does, the honeysuckle will wither away, leaving only scars. But if there is plenty of light for a while longer, perhaps because the dying mother tree was particularly large and so left a correspondingly large gap, then the young tree in the honeysuckle’s embrace can be smothered. Its untimely end, though unfortunate for the tree, brings us some pleasure when we craft its bizarrely twisted wood into walking sticks.
The young trees that overcome all obstacles and continue to grow beautifully tall and slender will, however, have their patience tested yet again before another twenty years have passed. For this is how long it takes for the dead mother’s neighbors to grow their branches out into the gap she left when she fell. They take advantage of the opportunity to build out their crowns and gain a little additional space for photosynthesis in their old age. Once the upper story grows over, it is dark once again down below. The young beeches, firs, and pines that have put the first half of their journey behind them must now wait once again until one of these large neighbors throws in the towel. That can take many decades, but even though it takes time, in this particular arena, the die has already been cast. All the trees that have made it as far as the middle story are no longer threatened by competitors. They are now the crown princes and princesses who, at the next opportunity, will finally be allowed to grow up.
7
— FOREST ETIQUETTE —
IN THE FOREST, there are unwritten guidelines for tree etiquette. These guidelines lay down the proper appearance for upright members of ancient forests and acceptable forms o
f behavior. This is what a mature, well-behaved deciduous tree looks like. It has a ramrod-straight trunk with a regular, orderly arrangement of wood fibers. The roots stretch out evenly in all directions and reach down into the earth under the tree. In its youth, the tree had narrow branches extending sideways from its trunk. They died back a long time ago, and the tree sealed them off with fresh bark and new wood so that what you see now is a long, smooth column. Only when you get to the top do you see a symmetrical crown formed of strong branches angling upward like arms raised to heaven. An ideally formed tree such as this can grow to be very old. Similar rules hold for conifers, except that the topmost branches should be horizontal or bent slightly downward.
And what is the point of all this? Deep down inside, do trees secretly appreciate beauty? Unfortunately, I cannot say, but what I can tell you is that there is a good reason for this ideal appearance: stability. The large crowns of mature trees are exposed to turbulent winds, torrential rains, and heavy loads of snow. The tree must cushion the impact of these forces, which travel down the trunk to the roots. The roots must hold out under the onslaught so that the tree doesn’t topple over. To avoid this, the roots cling to the earth and to rocks. The redirected power of a windstorm can tear at the base of the trunk with a force equivalent to a weight of 220 tons.19 If there is a weak spot anywhere in the tree, it will crack. In the worst-case scenario, the trunk breaks off completely and the whole crown tumbles down. Evenly formed trees absorb the shock of buffeting forces, using their shape to direct and divide these forces evenly throughout their structure.
Trees that don’t follow the etiquette manual find themselves in trouble. For example, if a trunk is curved, it has difficulties even when it is just standing there. The enormous weight of the crown is not evenly divided over the diameter of the trunk but weighs more heavily on the wood on one side. To prevent the trunk from giving way, the tree must reinforce the wood in this area. This reinforcement shows up as particularly dark areas in the growth rings, which indicate places where the tree has laid down less air and more wood.
Forked trees are even more precarious. In forked trees, at a certain point, two main shoots form, and they continue to grow alongside each other. Each side of the fork creates its own crown, so in a heavy wind, both sides sway back and forth in different directions, putting a great strain on the trunk where the two parted company. If this transition point is in the shape of a tuning fork or U, then usually nothing happens. Woe betide the tree, however, that has a fork in the shape of a V, with the two sides joining at a narrow angle. The fork always breaks at its narrowest point, where the two sides diverge. Because the break causes the tree distress, it tries to form thick bulges of wood to prevent further damage. Usually, however, this tactic doesn’t work, and bacteria-blackened liquid constantly bleeds from the wound. To make matters worse, the place where one side of the fork broke off gathers water, which penetrates the tear in the bark and causes rot. Sooner or later, a forked tree usually breaks apart, leaving the more stable half standing. This half-tree survives for a few more decades but not much longer. The large gaping wound never heals, and fungi begin to devour the tree slowly from the inside out.
Some trees appear to have chosen the banana as a model for their trunks. The lower part sticks out at an angle, and then the trunk seems to have taken a while to orient itself vertically. Trees like this are completely ignoring the manual, but they don’t seem to be alone. Often whole sections of a forest are shaped this way. Are the rules of Nature being set aside here? Not at all. It is Nature herself that forces the trees to adopt such growth patterns.
Take, for example, trees on high mountain slopes just below the tree line. In winter, the snow frequently lies many feet deep, and it is often on the move. And not just in avalanches. Even when it is at rest, snow is sliding at a glacial pace down toward the valleys, even though we can’t detect the movement with our eyes. And while the snow is doing that, it’s bending trees—the young ones, at least. That’s not the end of the world for the smallest among them. They just spring back up again without any ill effects after the snow has melted. However, the trunks of half-grown trees already 10 feet or so tall are damaged. In the most severe cases, the trunk breaks. If it doesn’t break, it remains at an angle. From this position, the tree tries to get back to vertical. And because a tree grows only from its tip, the lower part remains crooked. The following winter, the tree is once more pressed out of alignment. Next year’s growth points vertically once again. If this game continues for a number of years, gradually you get a tree that is bent into the shape of a saber, or curved sword. It is only with increasing age that the trunk thickens and becomes solid enough that a normal amount of snow can no longer wreak havoc. The lower “saber” keeps its shape, while the upper part of the trunk, left undisturbed, is nice and straight like a normal tree.
Something similar can happen to trees even in the absence of snow, though also on hillsides. In these cases, it is sometimes the ground itself that is sliding extremely slowly down to the valley over the course of many years, often at a rate of no more than an inch or two a year. When this happens, the trees slip slowly along with the ground and tilt over while they continue to grow vertically. You can see extreme cases of this in Alaska and Siberia, where climate change is causing the permafrost to thaw. Trees are losing their footing and being thrown completely off balance in the mushy subsoil. And because every individual tree is tipped in a different direction, the forest looks like a group of drunks staggering around. Accordingly, scientists call these “drunken forests.”
At the edge of the forest, the rules for straight trunk growth are not quite so strict. Here, light comes in from the side, from a meadow or a lake—places where trees just don’t grow. Smaller trees can get out from under larger ones by growing in the direction of the open area. Deciduous trees, in particular, take advantage of this. If they allow their main shoot to grow almost horizontally, they can increase the size of their crowns by up to 30 feet, thanks to their radically angled trunks. Of course, the trees then risk snapping off, especially after a heavy snowfall, when the laws of physics come into play and the lever principle exacts its tribute. Still, a shorter life-span with enough light for procreation is better than no life at all.
Whereas most deciduous trees leap at chances to grab more light, most conifers stubbornly refuse. They vow to grow straight or not at all. And off they go, always opposing gravity, directly up in a vertical direction so that the trunk is perfectly formed and stable. Lateral branches encountering light at the forest’s edge are permitted to put on noticeable girth, but that’s it. Only the pine has the cheek to greedily redirect its crown toward the light. No wonder the pine is the conifer with the highest rate of breakage because of snow.
PINE
8
— TREE SCHOOL —
THIRST IS HARDER for trees to endure than hunger, because they can satisfy their hunger whenever they want. Like a baker who always has enough bread, a tree can satisfy a rumbling stomach right away using photosynthesis. But even the best baker cannot bake without water, and the same goes for a tree: without moisture, food production stops.
A mature beech tree can send more than 130 gallons of water a day coursing through its branches and leaves, and this is what it does as long as it can draw enough water up from below.20 However, the moisture in the soil would soon run out if the tree were to do that every day in summer. In the warmer seasons, it doesn’t rain nearly enough to replenish water levels in the desiccated soil. Therefore, the tree stockpiles water in winter.
In winter, there’s more than enough rain, and the tree is not consuming water, because almost all plants take a break from growing at that time of year. Together with belowground accumulation of spring showers, the stockpiled water usually lasts until the onset of summer. But in many years, water then gets scarce. After a couple of weeks of high temperatures and no rain, forests usually begin to suffer. The most severely affected trees are those that grow in soi
ls where moisture is usually particularly abundant. These trees don’t know the meaning of restraint and are lavish in their water use, and it is usually the largest and most vigorous trees that pay the price for this behavior.
In the forest I manage, the stricken trees are usually spruce, which burst not at every seam but certainly along their trunks. If the ground has dried out and the needles high up in the crown are still demanding water, at some point, the tension in the drying wood simply becomes too much for the tree to bear. It crackles and pops, and a tear about 3 feet long opens in its bark. This tear penetrates deep into the tissue and severely injures the tree. Fungal spores immediately take advantage of the tear to invade the innermost parts of the tree, where they begin their destructive work. In the years to come, the spruce will try to repair the wound, but the tear keeps reopening. From some distance away, you can see a black channel streaked with pitch that bears witness to this painful process.
And with that, we have arrived at the heart of tree school. Unfortunately, this is a place where a certain amount of physical punishment is still the order of the day, for Nature is a strict teacher. If a tree does not pay attention and do what it’s told, it will suffer. Splits in its wood, in its bark, in its extremely sensitive cambium (the life-giving layer under the bark): it doesn’t get any worse than this for a tree. It has to react, and it does this not only by attempting to seal the wound. From then on, it will also do a better job of rationing water instead of pumping whatever is available out of the ground as soon as spring hits without giving a second thought to waste. The tree takes the lesson to heart, and from then on it will stick with this new, thrifty behavior, even when the ground has plenty of moisture—after all, you never know!
The Hidden Life of Trees: What They Feel, How They CommunicateDiscoveries from a Secret World Page 4
