How will trees, shrubs survive severe winter weather?

Gardeners may be wondering just how, and if, trees, shrubs and perennials survive below-zero temperatures. They know that the below-ground parts of a tree are kept insulated by a layer of snow, and that is important to winter survival, but the exposed parts of a tree are not so protected. Horticulturists with Iowa State University Extension and Outreach explain the cold hardiness of trees, shrubs and perennials.