Ever wonder how trees can live hundreds, if not thousands of years in snow, cold winds, icy precipitation, and long periods of below freezing temperatures? Like the rest of us, trees slow down in winter. Deciduous trees lose their leaves and shut down photosynthesis entirely, while trees with needles that remain (i.e. evergreen trees) have the ability to photosynthesize in winter. Bark works as an insulator protecting the living tissue just below from freezing temperatures. Bark also acts as a defense mechanism protecting the tree from antler rubbing, insects, fire and sun. Bark can also serve other functions like helping to preserve some of humans favorite libations or cushioning our feet.

Pictured is a cross section of Cork Oak. Yes, that bark is where all of our wine bottle corks and footwear cushions come from. That thick bark does an incredible job of insulating the living tissue and protecting it from the sun’s rays.

However, trees can be negatively impacted by winter weather, especially in Colorado, by a phenomenon called sunscald. In the winter the sun moves into the southern hemisphere, which means it’s radiation often shines directly on the trunks of trees rather than down on the crown as in the summer. For mature trees with thick bark the sun’s rays usually do not cause damage because they do not heat up the interior living tissue enough to thaw it out of dormancy. For young trees this is a different story. Their thin bark heats up from the sun on the south side causing the cells to move water. The cells can then desiccate or burst upon freezing when the temperature drops in the night. In the natural ecosystem, young trees typically grow up in a sheltered forest where other trees shade them from the winter sun.

A great way that humans can help protect young trees that aren’t in a native forest is by protecting the south side of the trunk with a protective barrier. We like to use recycled corrugate cardboard for this purpose because it insulates much better than the thin paper wrap. It also fits our values of re-using discarded materials that decompose quickly.

We usually recommend protecting trees from November- April. And you don’t have to take our word for it! For more extensive information on sunscald check out this link WSU Sunscald and Sunburn Article

Trees protected from rays of the winter sun

Sunscald on a tree trunk

Did this article peak your curiosity? Want to meet with your local Arborist to learn more?