Aspen leaves flutter, tremble, shiver and quake
THE Aspen is a lovely tree. A member of the poplar family, it is native to Ireland and has one of the most wind-sensitive leaves of any of our wild plants.
A typical plant leaf is composed to two parts: the flat leaf blade and the stalk supporting it. Aspen leaves have blades that are pale green in colour, are roundish or bluntly triangular in shape and have irregularly toothed margins. The leaf stalks are long and very flattened.
The long and very flattened leaf stalks result in the Aspen having a rather unique characteristic: the leaf blades flutter, tremble, shiver and quake in the slightest breeze.
Sometimes, in that twilight zone between stillness and a freshening breeze, the multitude of leaves on a mature Aspen tree will tremble so violently that, before the tree is seen, the sound of it may be heard like distant subdued applause.
The tree’s specific botanical name in Latin is ‘ tremula’. In Irish, the Aspen is known as ‘an crann crathach’: the vibrating tree. Why the leaves tremble and vibrate in the breeze is unknown. Why there needs to be a reason for everything is questionable, but since the scientific tradition demands that everything needs to have an explanation here are some of the suggestions put forward.
One suggestion is that the fluttering may be an adaptation to strong wind. By going with the flow, the twisting and turning leaf is less prone to damage than it would be if it stayed rigid and resisted the force of the wind.
Another suggestion is that when all the leaves on a tree tremble the effect is to allow more light to penetrate the foliage thereby improving the tree’s ability to make food or photosynthesise. When the leaves high in the canopy move, they allow light to flood down to energise the more shaded leaves below.
Another suggestion linked to photosynthesis is that moving leaves are more efficient at exchanging gasses than static leaves.
Some argue that the movement may be a pest deterrent; insects are less likely to try to feed on, or lay on, leaves that are in constant motion.
A final suggestion is that the fluttering serves no purpose at all but is merely the chance result of the combination of the very flattened leaf stalk and the way it is set perpendicular to the surface of the leaf.
Whether trembling bestows any biological advantage to Aspen leaves remains a mystery.