…when the leaf falls from the tree.

Above, the leaf scar from the Kentucky Coffeetree in the front yard, planted from seed 4 or 5 years ago. KCTs have enormous compound leaves, and this tree, though taller than me and growing fast, had just 30 this year. It still looked extravagantly foliated.
If you look closely at the scar you can see the vascular bundles, the pipes through which water and minerals flow into the leaf and where sugars (food) flow outward to the rest of the tree, including the roots.