Crown Shyness – The Mystery of Coyness in the Canopy

A basic human reaction to being near someone you don't want to be near is simply to move away.  Something like that happens with a number of tree species.  Their crowns do not touch each other at the canopy level.  Yet, the true reason for this adaptive behavior (which helps a species to cope in its environment with greatest success and least conflict with others, including its own) is still something of a mystery.  A number of reasons have been put forward, but none proven definitively.  If only the trees could talk…

More exactly, the reasons for crown shyness is believed to vary across different species.  Crown Shyness was first given its name over a century ago and since then it has been hypothesized that the reasons for this are multiple – with one species having a reason for manifesting this striking behavior while others have different reasons.

As such it is thought that crown shyness is an example of convergent evolution (which happens when unrelated animals or plants evolve to look or act alike because they face the same challenges).  Whatever the reasons, the beauty of canopy shyness lies, for me. in the delicate way tree crowns seem to respect each other's space, creating lace-like gaps in the roof of the forest.

The first hypothesis is that when the canopy branches of trees come into contact with each other they get damaged.  This is known as mechanical abrasion and is caused (mostly) by leaves and branches hitting each other in the wind.  In order to test this idea out, trees have been artificially prevented from doing this and, little by little, the gaps in the canopy are filled in. 

Supporters of this idea say crown shyness is often seen in places where branches rub and break, like in windy forests, forests with bendy trees, or young forests. They believe that how flexible the side branches are plays a big role in how much the tree tops avoid each other.

And then there is light. One popular idea is that crown shyness happens because trees can sense light changes caused by nearby trees. Plants have special light sensors that help them notice when another plant is close, by picking up changes in certain types of light, especially far-red and blue light. When they sense this, they try to grow away from the neighbor to avoid getting too much shade. This helps explain why some tree tops don't touch each other; it's their way of avoiding competition for sunlight.

Sometimes it is simply the a shade avoidance response.  A Malaysian scientist (Francis S.P. Ng) discovered that the leaves of the Borneo Camphor Tree stopped growing when they were near adjacent leaves because of the shade.  So, crown shyness (at least in some species) could be explained because the trees “know” that they won’t grow very well in the shade, so avoid it.

Did we say it's also visible from above?

Crown shyness may also occur to limit the spread of diseases and insects – but this particular train of thought is not considered very likely.  Insects can still easily move across those small gaps or fly around. So crown shyness is more about how trees grow and protect themselves than about keeping insects apart. Whatever the reason for crown shyness – and it seems it really does depend on the species - one thing is for sure – when it happens the result is startlingly beautiful.

 Fist Image Credit