Tree cells in the cambium layer (just under the bark) have a unique way of avoiding freeze damage. If ice crystals get into the cambium, the cells begin to shrink by losing water. This allows the ice crystal to grow without rupturing the wall of the cambium cells. When the ice melts the cambium absorbs the water from the melting ice and expands to its former size. Trees are incredibly designed to exist in a myriad of climatic and environmental conditions. They certainly are some of God's greatest gifts to man.