For a long time, even I did not know how slowly trees grew. In the forest I manage, there are beeches that are between three and seven feet tall. In the past, I would have estimated them to be 10 years old at most. But when I began to investigate mysteries outside the realm of commercial forestry, I took a closer look.
An easy way to estimate the age of a young beech tree is to count the small nodes on its branches. These nodes are tiny swellings that look like a bunch of fine wrinkles. They form every year underneath the buds, and when these grow the following spring and the branch gets longer, the nodes remain behind. When the branch gets thicker than about a tenth of an inch, the nodes disappear into the expanding bark. When I examined one of my young beech trees, it turned out that a single eight-inch-long twig already had 25 of these swellings. I carefully extrapolated the age of the tree to be at least 80 years, 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 per season. Unfortunately for them, their 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 three 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 has been used by generations of foresters to refer to this kind of behaviour.
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 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 close wounds 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. Dr. Suzanne Simard of the University of British Columbia, 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 youngsters’ upbringing. “My” small beech trees, which have by now been waiting for at least 80 years, are standing under mother trees that are about 200 years old – the equivalent of 40-year-olds in human terms. The stunted trees can probably expect another 200 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 in 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 it is in waiting mode. It is not getting sufficient light 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. 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 young trees that overcome all obstacles and continue to grow beautifully tall and slender will, however, have their patience tested yet again before another 20 years have passed. For this is how long it takes for the dead mother’s neighbours 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 storey 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 neighbours throws in the towel. That can take many decades, but even though it takes time, all the trees that have made it as far as the middle storey 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.