Why Trees Don’t Touch: The Science and Philosophy of Crown Shyness

You probably know that one of the founding principles of science is Occam’s Razor — the theory that the simplest answer is most likely to be correct. But the problem with this theory is that it removes the awe from science. When we understand a process and see it reduced to its basic mechanics, it’s hard to be overwhelmed by intrigue and wonder anymore.

Sometimes we hang onto ‘miraculous thinking’, reaching out for God in the machine, even when Occam’s razor is right there within our grasp…

Crown shyness is this mesmerising phenomenon, where the tops of trees don’t quite touch one another, so that, from the ground, the canopy appears to be fractured by myriad tiny rivers of sky. Let’s turn to a more conventional river for Occam’s explanation…

Walking along the banks of this river, a young child asks their dad;

“How do the trees know to stay out of the water? It’s thick woodland on the bank, but it suddenly ends at the river’s edge.”

Looking upriver, the dad sees a perfect divide between the trees — water splitting the woodland in two, with nothing growing in the river itself. Of course, as a ‘grown up’ he knows that the answer is obvious:

“The seeds can’t settle in the water — and most trees don’t like growing in the wet. Those that do, get swept away by floods, leaving the riverbed clear of any trees.”

Now the child turns skywards, her eyes filled with curiosity as she notices the canopy — the tops of trees above her held apart by breezy fissures — canopy shyness;

“And why do the trees have gaps between them?”

Yet this time, the dad answers differently:

“Some scientists believe that the tree’s leaves can see light reflected from neighbouring trees. They think that the tree somehow knows its own shape and uses its sight to see which branches need to grow. Scientists think that the tree uses this sight to stop its branches being shaded, and stop creepy crawlies from reaching its leaves.”

“But daddy, the trees do touch sometimes — I can see it — when the wind pushes them into each other.”

The dad, confounded by reality, looks up and takes in the canopy, realisation creeping across his puzzled expression.

A mature oak tree weighs slightly less than a double decker bus. When its branches are fully laden with leaves — dense and heavy with moisture, the tree takes longer to get up speed than in winter. But, with a greater mass, it can cause greater damage on impact. We know that much from seeing what happens when the tree falls down. Now, imagine that you’re up in the canopy during a summer storm — twigs whipping around and the whole tree crashing inevitably from one side to the other.

The force of this is enough to destroy leaf buds on the margins of the canopy. But you don’t have to take my word for it — a 2024 study quantified it, rigging an Oak tree up with accelerometers, before replicating these forces on the ground to find that some buds survived impacts better than others. Clusters of buds dealt better with the regular impact of storms, but there was still damage. And damage to these growing tips will, unsurprisingly, affect the way that a tree grows.

Gardeners know that if you snip off a twig just after a bud, the growth of that branch will follow the direction the bud is pointing. I use this method all the time to shape my hedges and trees. So, what happens if the buds and twigs all around the edge of a tree are knocked off? The growth will head back in the opposite direction — towards the tree’s interior. Not due to some marvellous plant vision — it’s just hormones. Growth hormones are what causes a tree branch to grow in the first place — lop off a bud and the local growth hormone concentration will drop, redirected to the next bud in line, which typically faces the opposite direction (buds are usually stacked left, right, left along a branch).

It might be easier to picture crown shyness like a tree being surrounded on all sides by hedge trimmers. Each time the wind catches the branches, it whips into the blades, so that over time it is perfectly trimmed. I had a tree growing for several years in my back garden two feet from a gleaming white wall. The branches never quite reached the wall. Yet on the other side the tree grew much further. Why? Because whenever storms came and whipped the tree around, it would jostle against the rough surface, knocking off terminal buds, redirecting the growth elsewhere.

This explanation for crown shyness isn’t a satisfying one, but it’s generally accepted in the scientific community. In fact, you can find it mentioned back in papers from the 1980s, and many studies report broken and abraded twigs and branches along the edges of a tree’s canopy. In fact, a 2015 study found that at least 50% had been broken in the previous 6 years. So why is it that other theories of crown shyness still persist?

The problem with Occam’s razor is that the most logical explanation isn’t always the most satisfying one. If you actually spent some time in a tree canopy during a storm, I think you’d be pretty convinced, but we mostly live down on the ground. It’s easy to romanticise processes which occur way up in the air, and mysticise the biology of trees, which are, after all, the source of much of our folklore. It’s true that there are fantastical things about trees — the mycorrhizal network must rank as one of the most surprising discoveries of the past century (and perhaps the hardest to spell). But the scientists who focus on plant vision and plant consciousness have lost sight of the real miracle.

Human beings, rivers and crown shyness are all miraculous in their own way. Millions of interacting, chaotic processes somehow combine to create something ordered from disorder. An emergent phenomenon is created from the apparently random jostling of physics, chemistry and biology — shaken up in a sack and tipped out like marbles across the carpet of the universe.

It’s sad that we’ve lost much of our mysticism — religion may be problematic, but it also transcended culture and fostered community. Belief hacks deep into our brains, and wacky concepts like tree consciousness and tree vision tug hard at that vestigial religious remnant, crying “remember me?”. But there is a glory in nature which is hard to express in words. There is a German word — ‘waldeinsamkeit’ — which means the sublime or spiritual feeling of being alone in a woodland. It’s the very thing that inspires people to hunt for explanations for crown shyness in the first place — we see something very nearly magical, and resolve to explain it with pseudoscience and mysticism.

What if, instead of seeking mystic explanations, we sat with our doubts and with our clarity, looked up at the great beauty, sank into the wilderness and just appreciated it for what it is — order from chaos?