Why do trees lose their leaves?

Question

Please give me a simple answer, one that a 15-year-old could understand. Thank you.

Answer 1

First and foremost, not every type of tree loses its leaves. Only deciduous trees lose their leaves. There are two important factors related to this process: light and temperature.

In many cases, deciduous trees grow in areas that experience cold, harsh winters. Trees drop their leaves to shield themselves during these winter months, because the dry cold winter winds will cause the trees to lose their moisture and the leaves have a large surface area. By shedding their leaves, the trees can preserve the moisture in their branches and trunk, instead of drying out and dying. Also, a tree without leaves is in a state of dormancy and needs less energy to remain alive.

In the spring and summer, leaves photosynthesize the ample sunlight that falls on them. This produces chlorophyll, which causes the green coloring. Photosynthesis generates energy for the tree, and the tree takes in nutrients from the soil to feed its leaves and keep them healthy. The warm and bright colors that the leaves take on in fall have actually been present the whole time, but they have been masked by the chlorophyll. As the days get shorter, the trees receive less sunlight, and therefor produce less chlorophyll. Then they fall off, because the tree does not have the energy to support them through the winter. 

Answer 2

Why do trees lose their leaves? Because in winter, our area of the Earth is receiving less sunlight, and the air becomes colder. While these changes are happening, the trees are preparing for winter. When a tree sheds its leaves, the spots where the leaves connect are closed off. Liquids will not flow in and out of the leaves, which change in color and fall off.

During the warm seasons, leaves use air, water, and sunlight to generate food for the tree. Throughout that process, the tree emits a large amount of water through small holes in the leaves. In the winter, the tree doesn’t receive enough water to replace what is lost through those holes. If the tree were not to seal off the spots where leaves grow, it would dry out and die. When spring comes back, the air is warmer and the tree is able to receive more water again, so it grows new leaves.