Frost-triggered Leaf Fall

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Yesterday saw wind gusts exceeding 20mph here, and steady winds of 10mph or more, yet a couple of birch trees near our house held most of their yellow leaves. After last night’s hard frost, though, we awoke to a windless morning and a cascade of yellow leaves from those same trees, seen in the attached video. If you turn up the sound, you can hear them as they hit the frozen leaves on the ground. (The louder, occasional hollow knocking noise is water drops coming off our roof.) A couple hours after taking the video the trees were nearly devoid of leaves. Apparently a frost can harden the tree’s abscission layer (the zone between the leaf stem and branch), effectively severing the leaf’s connection to the tree.

 

Steve Wilson

Isabella