I think the idea behind calling it "shaking" is these branches and leaves that are already cut (inaccessible from the root), and just need a strong breeze to shake the tree and make them fall out.
We had an ice storm this year and there are loads of them all over town still.
I think the idea behind calling it "shaking" is these branches and leaves that are already cut (inaccessible from the root), and just need a strong breeze to shake the tree and make them fall out.