The shyness of trees

Tree or ‘crown shyness’ is where the uppermost branches of different trees in a forest canopy avoid touching one another. This stand-offish approach creates clearly defined borders when viewed from below the forest canopy appears to fit together like some crazy paving project with the sky highlighting each seemingly random shape. It’s well worth looking up for, but why it happens we do not know.

Some of the more ‘creative’ writers call it a phenomenon; the phenomenon of crown shyness. Personally, I don’t like the term, calling something a phenomenon suggests acceptance of the unexplained, a phenomenon is only just a smidgen away from a miracle. Acceptance of miracles is… ‘unscientific’ to say the least. So, trees are shy and we don’t know why.

Some say the separation is simply caused by the trees rubbing against one another. As branches from different trees collide with each other in the wind, buds and meristems suffer physical damage and the resulting damage is what we see. The ‘They’ have even given this a name; ‘Reciprocal Pruning’. My issue with Reciprocal Pruning, that that branches on the same tree also collide with each other in the wind, therefore there should be void around every branch on every tree, but there is not.

Others suggest the separation is simply the result of mutual shading. Tree canopies shade each other and prevent lateral growth. As with Reciprocal Pruning, branches on the same tree shade their lower branches, therefore, there should be void around every branch, but there is not. I don’t subscribe to the mutual shading concept either.

If you subscribe to the idea that a forest is, in fact, a mega-organism; a community of interacting organisms working together to accomplish more than they could alone. Then crown shyness makes sense – by not competing against each other individual trees can invest and/or share resources elsewhere. By letting light in, other plants and organisms can prosper. All for one, and one for all. But, that is why, not how.

How, has most likely got to do with light. Plants may able to sense the proximity of their neighbours by recognising the type of light that they receive – the unique photoreceptor idea.

Let’s pretend for a moment that we all paid attention in science class – for some, including myself that may be harder to do. Light, as you recall, is made up of a spectrum of electromagnetic waves with visible light (the bit that we can see) being a just small part of that spectrum. When ‘light’ contacts an object (i.e. a leaf) it can be absorbed, reflected, refracted or transmitted.

With this in mind, once the light has contacted the object, our leaf, the resulting residual light is no longer the same; because some of the electromagnetic waves have been absorbed and others distorted (to some extent). The unique photoreceptor idea, is that a plant can determine where its light comes from based on the type of electromagnetic waves that it receives – it can distinguish between reflected, refracted or transmitted light and/or differing combinations thereof. By knowing where its light is coming from, it can work out which way it should grow or not grow as the case may be.

Fantastic yes, but phenomenal no. It’s actually all rather mechanical; photoreceptors, (the bits inside a plant that receive light) are tuned to the electromagnetic waves they receive and need. Kind of like tuning a radio to select a station. If photoreceptors need country music, then they will be ‘tuned’ into the electromagnetic waves that deliver country music, if like most of us they don’t need country music, then they will be tuned to receive something else. No miracles.

While I might not be able to distinguish between reflected, refracted or transmitted light I can tune a car radio (and I can live without country music). Finding out why or how strange things happen, doesn’t make the happening any less strange or less fantastic. Fantastic things happen all around us every day – sometimes we just need to look up.