Winter Survival; Trees

Gentle snow fell in Northwestern Minnesota in early October this year, providing a wintertime preview. Surviving winter temperatures far below freezing is a big challenge for plants and animals. Today’s post focuses on how trees make it through — with some scenic pictures of the recent snow.

Trees are largely comprised of water, a critical issue for trees in the winter is to prevent water within living cells from freezing to crystalline ice. An important consideration is that most of the cells within trees are not living; freezing dead cells within trees happens commonly with no harm. Living cells avoid freezing by expelling water into the space between cells, increasing the sugar content of their remaining water, and transitioning this intracellular fluid to a viscous glass-like state.

Another winter-time issue for trees is water loss. To avoid excessive water loss, deciduous trees drop leaves with their large exposed surface area. Needles on evergreen trees minimize water loss because of their smaller surface area and their waxy outer coating.

Despite these coping mechanisms, extremely cold temperature does damage trees. If the water-bearing sap within trees freezes, the resulting expansion can literally cause trees to explode. Issues are also caused by swings in temperature. A warm spell, or prolonged sun exposure, can cause sap to flow, exposing the tree to damaging freeze in a subsequent cold snap.