We know that the leaves of some trees change color, and drop to the ground in the Fall.  By losing their leaves, trees protect themselves from the cold, sometimes freezing, tempatures of Winter.

Stems, twigs, and buds are equipped to survive extreme cold. Tender leaf tissues however, would freeze in winter, so plants must either protect their leaves or shed them.

The evergreens — pines, spruces, and hemlocks – are able to survive winter because they have developed a way to protect their foliage.

Instead of flat leaves, pine trees have needles.  These needles are the key to the Winter survival of the pine tree.  Needles cut evaporation so trees can save water — dear in the winter. The narrow leaves manage this with three adaptations:

• thicker skin, to retain water
• a thicker coating of water-proof wax, called cutin 
• simpler needle-like shape. The long, slender shape reduces leaf surface area, which, in turn, reduces the amount of water vapor escaping the leaf, or needle.

(Source: U.S. Forest Service; Pallardy,Stephen, and Kozlowski, TT. Physiology of Woody Plants. Academic Press, 2007)