You’re right, each year during the fall, we often see a lot of trees dropping their leaves. To find out exactly what happens when leaves fall, I talked to my friend Henry Adams, a researcher at Washington State University.
The chemical that helps a tree keep its leaves is called auxin. Meanwhile, a chemical called ethylene helps flowers open, fruit ripen and leaves fall.
“There are these two chemicals, and they are sort of fighting it out throughout the year,” Adams said.
Instead of continuing to make leaves that would otherwise just die during a frost, the trees store up some nutrients from their leaves in other parts of the tree before the winter. Then they drop their leaves. For some trees, it’s better just to have bare branches during the cold seasons. It will help them survive.