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Why Trees Don't Wear Sweaters

January 25, 2011
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No matter what area of the country you were in the past month, you experienced some extreme cold weather - even in areas that usually have fairly moderate temperatures. From Atlanta to Texas, it was cold!

At least we have the option of bundling up with scarves, mittens, hats and coats, and we can even warm up with a nice toasty cup of hot chocolate once back indoors. Alas, our tree friends aren't so lucky.

They can't bundle up or come in from the cold. They have to stand strong and endure the long winter. Maybe that's one of the reasons the mighty oak is so, well, mighty. He tolerates attacks from desiccating winds, snow and ice. Sure, all may be calm below ground, where tree roots can be kept insulated under snow and soil; but the picture changes as you climb. Imagine standing still and anxiously watching the ice dangle off your arms and fingers until it melted - Brrr!

Luckily for our leafy friends, deciduous trees like the oak go into a rejuvenation phase known as dormancy. It's how they adapt to lower temperatures. They lose their leaves, store up some reserves and hunker down, saving up their energy.

winter needle

Even evergreens become inactive in the winter, though they don't lose their needles all at once like their deciduous counterparts. They shed the oldest needles in the fall. Fewer needles allow them to minimize exposure to desiccation, but needle retention gives them an advantage: they can begin photosynthesis earlier in the spring, while deciduous trees must wait a bit longer so as not to risk bud damage.

Though it seems like a tree would freeze to the core in this frigid air, that's actually not the case. In fall, trees convert starch to sugars, which act like an antifreeze. Try the soft drink experiment - place a diet soda and its regular soda counterpart outside during sub-freezing temperatures. The diet variety will freeze solid much sooner since it lacks the high sugar content.

Also helping trees avoid freezing are the more pliable membranes and liquid cells that become so thick they are almost solid. Since a tree is made up of both live and dead cells, and water needs a place to go as it moves through a tree, the dead cells can and do freeze. As long as a tree can keep its live cells from freezing, it can survive the winter practically unscathed. Thanks to Paul Schaberg, a research plant physiologist with the USDA Forest Service's Northern Research Station in Burlington, Vt., and his studies of trees' cold tolerance for that data.

So next time you're inclined to take a wool blanket out to your favorite tree, keep your hands free for a cup of warm tea instead. Enjoy the splendor that tree brings in winter, stretching out its skeleton as it glistens and glitters while donned in snow and ice crystals.

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