In most trees, leaves give off enormous amounts of water. In fact, in some, more than 90 percent of the water absorbed by roots and transported to the leaves is lost through evaporation.
For most broad-leaved trees, such as oak, chestnuts, ash and maples this would be impossible to sustain in winter when the ground is frozen and they would die through lack water. So these deciduous trees drop their leaves in autumn to protect themselves.
Certain trees, however, like pines and firs have developed another strategy to avoid drying out. Their leaves are needlelike and covered in a waxy layer that prevents evaporation. They do not need to drop their leaves in autumn because their water requirements are low. When individual leaves do fall, new ones replace them and the branches never look bare.