Why are evergreen trees pyramid shaped?
Evergreen conifers weathering the winter. (Image courtesy Sophia Lemon.)
An Earth & Sky radio listener asked, “Why do most evergreen trees have a pyramid shape? Does this shape help support the winter snow?”
Many of these trees grow in places that have severe winters. And the shape of this sort of tree does help keep wet, heavy snow off the tree’s upper branches. Conifers also tend to have shallow roots. They lack long, sturdy tap roots, so they’re subject to being knocked down by wind. Their shape reduces wind resistance and helps keep the tree standing upright.
What’s more, the major branches of conifers are layered, with an open area between the layers. This helps wind pass through, and it helps the tree get enough light, especially when sunlight comes in at a low angle as it does during the winter months. The tree’s shape lets it get even more light. The top branches don’t shade the bottom ones. It’s also noteworthy that the trees have needles instead of broad, flat leaves – in climates that sometimes feature abrasive, blowing ice crystals.
So those who admire the shape of a Christmas tree might want to recall that its shape has evolved in response to wind, snow, and light.
Our thanks to:
Dr. Colin Allen
Dept. of Philosophy
Texas A & M University
College Station, Texas
Dr. William K. Smith
Head, Dept. of Botany
University of Wyoming at Laramie
More Resources:
“Conifers.” c 1997. Britannica Online. Chicago: Encyclopedia Britannica, Inc.
Horn, Henry S., 1971. The Adaptive Geometry of Trees. Princeton: Princeton
University Press.
Sakai, A., and W. Larcher, 1987. Frost Survival of Plants. New York:
Springer.
Smith, William K. and Carol A. Brewer, 1994. “The adaptive importance of
shoot and crown architecture in conifer trees.” Amer. Naturalist 143:
528–532.
Sprugel, Douglas G., 1989. “The relationship of evergreenness, crown
architecture, and leaf size.” Amer. Naturalist 133: 465–479.
Tranquillini, W., 1979. Physiological Ecology of the Alpine Timberline. New
York: Springer.
