The next time you walk through a forest, take a close look at the trees all around you. You’ll notice that most of their lower branches have fallen off. But if you look at a tree growing out in the middle of your yard, most of the lower branches will still be there (unless someone has cut them off, which is what happened to my maple). Can you guess why?
In a forest, each tree is surrounded by lots of neighboring trees. And each leaf on each tree is competing for sunlight. The leaves on the trees’ top branches get plenty of sun, but leaves closer to the ground have access to much less light.
A tree growing on its own in the middle of your yard doesn’t have this problem. The entire tree gets lots of sunlight, so all its leaves can make food all day long.
Over time, the leaves on lower branches of forest tress shrivel and die. And since the main purpose of a branch is to hold leaves, the branches die too. Then they fall off. As a result, the tree can use its precious energy to support the parts of the tree that are absorbing sunlight and producing sugary food.