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Do Trees Hibernate In Winter?

Written by Dirk Bakhuyzen III | Friday, December 19, 2014

Everyone notices in the fall when trees put on their spectacular leaf show in order to preserve their resources to make it through the long, rough winter they face. But when those leaves are gone and the trees are once again bare-branched, we don't think much about them. Unless there is an ice storm or a tree comes down on top of a building or road - and then it's only because we have to.

But what do trees do to survive the winter and make it through until they can blossom and bloom again? Well, it's not hibernation because hibernation is what endothermic animals like mammals do; it's defined as “a state of inactivity and metabolic depression in endotherms...characterized by low body temperature, slow breathing and heart rate, and low metabolic rate.” With plants, including trees, this process is called dormancy instead, which is a life-cycle period during which growth, development, and physical activity are temporarily stopped, helping an organism to conserve energy.

Trees begin to go dormant in the fall when environmental cues like cooler temperatures and shorter periods of daylight alert them to the necessity of scaling back in order to conserve their core resources. Trees do not make food in the winter. Leaves then become a liability, so they shed them, often spectacularly, via the production of a chemical called abscisic acid (ABA). ABA prevents cell division and impedes growth in both deciduous trees and conifers (which do not lose their needles in fall, but do go into dormancy. With fewer parts to nourish, the tree can maintain its dormant core with stored nutrients.

Trees must also survive colder temperatures. Most of their surface area is exposed to the air and therefore vulnerable to freezing. The way that trees modify themselves to survive cold is also somewhat incredible. They actually change their membranes so that water migrates from inside of cells to the spaces in between cells. This makes them more pliable. Trees also convert starches to sugars in the fall, and these sugars act in the same capacity as antifreeze, lowering the overall freezing point of the tree. The sugars remain in the cells themselves. The water in between cells remains water and will freeze, but all living tissues are preserved.

While winter seems harsh to humans, trees native to colder climates are meant to experience dormancy, so it would be counterproductive to take measures to “spare” them. Of course, trees transplanted from other climates or ecosystems are different and must have a different kind of care. If you need advice on how to best care for any of your trees, do not hesitate to contact an expert at Chop. That is the area of our expertise.

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