The Avenue Effect in Trees

My thanks to Alun for sending in this photo of autumn colour near the Kitano Tenman-Gu Shrine in Kyoto. And the following question:

“I saw this on an email from National Geographic and was intrigued by the fact that the trees on both sides of the River are bending towards the centre! Albeit that the branches of the trees on the far bank are not extending as far as the branches of the trees on the bank from which the photograph has been taken. Any thoughts?”

Aside from the wonderful colours, what we are witnessing here is a fairly common effect, that I nickname the ‘avenue effect’. Tree branches grow towards the light, a botanical trend known formally as ‘positive phototropism‘. This is why we find them growing more towards the south in the northern hemisphere and vice versa.

But avenues are gaps and these gaps let in the light. This is why we often find tree branches growing towards the centre of avenues.

It is a similar effect and the same reason why we always find trees growing out and away from woodland at the edges, regardless of aspect – the ‘escape from the woods effect‘.

Breaking the Rules – Some thoughts for natural navigators

The shape in this picture will leap out at natural navigators, because the trees appear to be ‘breaking the rules’. They aren’t growing dependably out towards the south.

Once we are practiced at using the shape of trees to find direction, it is not long before we start to spot that there are a few situations where trees and other plants do like to ‘break the rules’.

Of course nature doesn’t break the rules, because the rules don’t really exist. They are trends that we simplify and package to help our memory.

When we feel things have ‘gone wrong’, it is always a case of taking a step back and remembering the basic botany that leads to the effects we see. This gets us out of trouble and solves any bizarre mysteries.

No rules are broken here, the avenue effect just means that the light is flooding in between the trees, leading to branches on opposing trees growing most strongly in opposing directions.

Image credit: Michael George

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