Wintering trees are not sleeping, but are simply still - truly counting the days until spring. Most of the growing points in the tree are protected inside jackets called buds. Only then will it be apparent whether the tree has put aside and saved enough resources to respond to the new season of growth.
Winter is a difficult time for trees.
Trees must stand in the face of drying and cold winds. Food reserves are carefully conserved for the coming needs of spring. Water continues to move through the tree until it freezes. Any creature needing a meal chews and nibbles on the resting buds and twigs. Trees stand alone against all circumstances that the winter season can generate.