I've just finished reading The Hidden Lives of Trees by Peter Wohlleben, which I thoroughly enjoyed.

According to the author, the advantage of shaking the leaves is that both sides of the leaf are exposed to the sun, and therefore both sides can photosynthesize. This would be in contrast to other species, where the underside is reserved for breathing and transpiring. However, to me (a complete amateur), the underside of a quaking aspen seems paler in colour and doesn't "look" like it's any more suited to photosynthesis than the underside of any other leaf.

In addition, I can't find any other sources that back this claim. Most other sources (for example https://www.nature.com/scitable/knowledge/library/case-study-the-glorious-golden-and-gigantic-13261308/) seem to claim the shaking of the leaves reduces the risks that come with too much sunlight, which damages the leaves and actually lowers the rate of photosynthesis.

My question is therefore, what is the most convincing advantage the quaking aspen gains from this characteristic ?

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    $\begingroup$ I would have to ask whether there is in fact any particular advantage, and indeed, whether aspens "quake" much more than other broad-leafed trees. My casual observation is that they really don't, it's just that they're often the only deciduous tree in areas with conifer forests, so the leaf movement stands out. $\endgroup$ – jamesqf Mar 25 '20 at 16:59
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    $\begingroup$ Quaking aspens do indeed "quake" in the merest of breezes, but aspen leaves are very light compared to maple or oak leaves and ave a flat petiole, another surface to catch the breeze. Maybe there is no benefit, it just is what it is. It's not like they attract other trees this way. $\endgroup$ – anongoodnurse Mar 26 '20 at 0:18
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    $\begingroup$ @anongoodnurse: Many other deciduous trees - cottonwoods, willows, maples, ash - have leaves that move in similiarly gentle breezes. But (at least in the western US) aspens are typically found in isolated groves (near springs, streams, & other places where there's plenty of water, surrounded by conifers, so the movement is noticable. $\endgroup$ – jamesqf Mar 26 '20 at 4:58
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    $\begingroup$ Hmm "why" do they quake? Impossible to know. The best the scientific process can do is determine if quaking provides any physiological or ecological advantages to the trees. I do not know of any specific research examining this (not too unusual) "phenomenon" in quaking aspen, but I'll dig around to see if I can find any interesting papers for you... $\endgroup$ – theforestecologist Mar 27 '20 at 6:05
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    $\begingroup$ Conjecturally: P. tremuloides is an early successional (i.e.,"foundational") species, and as a result is typically going to be exposed to more sunlight (due to less other plants shading them out). Their foundational role also means they use more of their energy to develop fast-growing foliage to out-compete other plants for sun (and therefore have less energy for developing UV defenses). I would guess that the added heat of the direct sun and less robust UV protection would decrease fitness, and so the plant would benefit from having less horizontal and still leaves. Natural selection etc.. $\endgroup$ – theforestecologist Mar 27 '20 at 6:15

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