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The Natural History of a Christmas Tree

December 23, 2009

No one really knows when the first Christmas tree was decorated in America. Winsor Locks, Connecticut says it was there in 1777. Easton. Pennsylvania claims German emigrants put one up in 1816, while Lancaster says it was in 1821 in that city. And others say it was in Boston. One thing is certain; Balsam fir has been a traditional Christmas tree in New England homes for generations.

As I sit here watching the lights twinkle on our tree it strikes me how little people actually know about Balsam fir now that most of them are grown and harvested on farms. We all live with one for weeks in our homes each year, but we really don’t know our friend much beyond the scent.

Balsam fir is the emblematic tree of the eastern North American boreal zone. It is found from the Canadian Maritime Provinces westward to Lesser Slave Lake and the Athabasca River in Alberta and southward through New England and the Great Lakes to Pennsylvania. Isolated populations also occur in northeastern Iowa, Virginia, and West Virginia.

You can actually get an approximate age of your tree before you even cut it down. The main trunk and branches both grow one new whorl each year and whorls that are shed as the tree grows older leave behind characteristic scars that encircle the main trunk. Counting the number of whorls and whorl scars from top to bottom will give you an idea of just how old your tree is.

In New England Balsam fir can be found in the high elevation montane fir forest and in northern New England in lowland boreal forests of northern Maine, New Hampshire and the Northeast Kingdom in Vermont. Individual trees in subalpine populations reproduce at a later age and die earlier than lowland trees. Life is harder in the mountains.

High-elevation forests are often marked by “fir waves”. These are crescent-shaped bands of dead trees that you can see in systematic patterns across the sides of the mountains. The waves are areas of standing dead fir trees with healthy trees surrounding them.

Fir waves move very slowly over decades in the direction of the prevailing wind. Wind velocity at the edge of the tree canopy is over 50% higher than within the forest. Rime ice forms on the trees when water droplets in the air hit solid surfaces and immediately freeze. Rime accumulates more on trees exposed to wind.

Trees at the leeward edge of the canopy opening in the wave are exposed to winds and die from loss of needles and branches due to heavy ice accumulation. The rocking in the wind with ice loads also causes their fine rootlets to break underground. These rootlets are important for delivering nutrients to the tree. As these trees die, adjacent trees experience the same conditions and begin to die. The overall direction of the wave motion is therefore directly related to wind direction.

Regeneration of waves occurs at about 60 year intervals. As you move back from the dying front of trees the trees are older and older until you reach the following wave of dead trees. If you were to take time lapsed photography of a mountain side, the waves of dead trees would appear to be moving across the mountainside like a wave in the ocean.

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