With this change, chlorophyll in the leaves begins to break down and dissolve. Within a few weeks, hardly any chlorophyll is left, and the other pigments are able to shine through. That's why we have the color change. At the same time, chemicals in the plant begin to break down cells near the base of the leaf. Eventually this layer will become so weak, that stray wind gusts and rain will cause the leaf to break off from the main stem.
Gravity does the rest as the leaf falls to the ground.
Explained scientifically, the process seems so simple and logical. But no amount of explanation can ever capture the beauty and grace of a crisp fall day as the leaves turn on their magical show. They are modified leaves that have lost their green color. Plants which drop their leaves in the fall are called deciduous.