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Why the aspen quakes

Unlike most leaves, aspen leaves have flat petioles, or stems.

Unlike most leaves, aspen leaves have flat petioles, or stems.

June 16, 2020 — Everyone has heard of quaking aspens, but do you know why they quake even when other trees are still? The answer is right there in the picture. Their leaf stems, or petioles, are flat, whereas in most other species the petioles are round. Round petioles tend to hold their leaves in one position but flat petioles allow the leaves to flutter in the slightest breeze. They may even allow the leaves to turn with the wind and avoid being stripped off in storms.

So now you know why those golden fall aspen groves seem to shimmer in the sunlight.

A few weeks ago we were warned to expect a storm front with high winds, and I was idly watching the aspens in my backyard to see when the front hit. By all indications it was dead calm outside; nothing was moving. But then I noticed one clump of aspen leaves fluttering. Not the whole tree, or even the whole branch. Just the one clump, as though there were a bird or squirrel hiding there. Then that clump grew still and one on the other tree started moving. You’d think both trees would flutter, or all the leaves on the same side, or something. But no, it was just a patch here, a patch there. All the other trees and shrubs remained immobile. I must have watched, intrigued, for 10 or 15 minutes. How could the breezes be so selective? Just a puff here, a puff there. It was like an invisible hand randomly touching the leaves.

It’s windy today and trees on all sides of the house are whipping around. How ordinary is that? Try watching an aspen dance in a dead calm. Now that’s interesting.

10 Comments »

  1. We lived in Colorado for a couple of years (40 years ago). There was a lovely grouping of Aspens in the back yard and I used to love to just look at them. It was very calming.

    • I couldn’t afford a mountain home when I finally moved here 15 years ago, so I planted some aspens for “atmosphere.” Not recommended for the city but I love them anyway.

  2. The variability of breezes is also evident on lakes or oceans. On a relatively calm day one can notice patterns of ripples. This is a significant factor in sailboat racing.

    I have a tulip poplar in our backyard and I was noticing yesterday that it has two-toned leaves. The downward sides are light and the uppers quite dark. Nature is interesting!

    • I got to do a little sailing as a kid. I remember watching for patches of darker (?) water to find the breeze. I guess that was from ripples on the surface. I miss sailing. It was a lot of fun.

      I wonder what purpose it serves for leaves to be a different color on the underside. Maybe the darker side absorbs more sunlight? But then why not make the whole leaf dark to begin with.

    • I did a little research and found that most leaves are darker on top because that side catches more sun and thus photosynthesis creates more chlorophyll on that side. I also read up on tulip poplars. Seems that’s quite a tree. How tall/old is yours? I’m jealous. My little yard is so small that I may end up regretting my aspens, which are already taller than I anticipated.

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