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Arb notes: overwintering in the Arb – arboreal methods of survival

During this very chilly week in February, it is hard to imagine staying outside in one spot the entire winter. Trees are unfortunately in this situation: if without the proper protections in place, their cells can freeze, and the tree will die. So how do they survive? There are many evolutionary adaptations trees have to endure the cold Minnesota winters. The first line of defense is bark, a tree’s thick outer layer, which insulates the inner tissues and can absorb heat. Another survival method is for a deciduous tree to drop its leaves during the fall. Because there is less sunlight and cold temperatures during the winter it is favorable for them to absorb the nutrients inside their leaves to store for the winter, and live off these energy stores until the spring. Some trees do not need to lose their leaves, however. Most coniferous trees, like the Eastern White Pine we have in the arboretum, don’t lose their leaves because their needles have a waxy coating which protects them from freezing temperatures, as well as prevents water evaporation. This way they can still photosynthesize during the winter. All trees then enter a dormancy period in which their cellular processes slow down. Because of this they do not need to use as much energy. Trees are also able to produce many types of proteins which aid in their survival during the winter. Some proteins can function as ice nucleators, around which ice crystals can form. If ice starts to form in the tissue, the crystals can form around these proteins instead of inside the cell, which contains all the necessary nutrients for its survival. In addition, trees also produce anti-freeze proteins, which help prevent the freezing process from starting within the tissues. With these adaptations, trees are able to effectively support themselves during the long, cold winter.

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