What does a deciduous tree do in the winter?

A deciduous tree simply survives in the winter. It maintains its energy, and attempts not to die using the food and water stored from the previous spring. It sheds its leaves in the fall for 2 reasons:
1) The leaves decompose and recycle nutrients throughout other organisms and through the soil
2) Once the leaves fall off, the tree doesn't have to focus on supplying energy to all the cells of the leaf, so it stores the food the leaf created, and sheds it for energy conservation.