When winter approaches, our part of Earth receives less sunlight, and the air grows colder. When these changes happen, trees prepare for winter. Trees that drop their leaves seal the spots where the leaves are attached. Then fluids cannot flow in and out of the leaves, which change color and fall off.
The falling of the leaves does more than mark the season. It also helps the tree survive the cold, dry air of winter. In the warm seasons, leaves use sunlight, water, and air to make the tree’s food. In that process, the tree loses a lot of water through tiny holes in the leaves. In winter, the tree does not get enough water to replace what it would lose through the leaves. If the tree did not seal the spots where the leaves grow, it would die. When spring brings warm air and fresh water, the tree will sprout new leaves and start growing again.