Our Bristlecone Pine Twisting Project
Bristlecone pines are the oldest trees in the world. Some approach 5000 years old! California's Ancient Bristlecone Pine Forest is just a few miles from the University of California's Barcroft Research Station, where Drake High has its cold frame project. We always pay several visits to the bristlecone pines whenever we go there.
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While strolling among the bristlecones, you are sure to notice that some trees have twisted trunks. They add to the beauty and other-worldliness of the scene. Many trees have straight trunks, though. Of the trees that twist, many grow counter clockwise as you look up their trunks, but a few grow the other way - clockwise. |
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Nobody seems to understand twisting in bristlecone pines, or in any other tree species for that matter. (Twisting is not limited to bristlecones.) There are a number of hypotheses that get repeated:
1) It's "just genetics" - twisting confers no particular advantage to the tree, and is not caused by environmental factors. Sort of like handedness in humans. Tree twisting should not correlate with environmental factors.
2) Twisting makes the trunk stronger and more resistant to breakage. If that were so, we would expect to find proportionallly more dead and/or broken tree trunks that are straight, and more living/unbroken trees that are twisted.
3) Phototropism: Just as sunflowers track the sun's daily progress across the sky, so do trees. This causes twisting. The twisting should be counter-clockwise as you look up the tree trunk. Trees with views of the western and eastern horizons blocked by ridges should exhibit less twisting.
4) Torque from prevailing winds: Since there is more foliage on the sunny (south) side of the tree, the prevailing (westerly) winds push on that foliage and twist the tree. The twisting should be clockwise as you look up the trunk. Sheltered trees should exhibit less twisting.
Surprisingly, all of these hypotheses can be tested without doing genetics. We just need to survey a large sample of trees and use statistics. In the spring of 2010 Drake Students will begin a twisting survey of bristlecone pines.
Data Table:
Grove (Patriarch vs. Schulman)
Name of trail within grove
latitude
longitude
elevation
Tree species (bristlecone vs. limber)
alive vs. dead
broken trunk?
trunk diameter at chest height
trunk twisting: Clockwise, counterclockwise, neither?
Angle of horizon to east?
Angle of horizon to west?
what else?
Materials:
handheld GPS
clipboard
measuring tape
compass
clinometer to measure angle of eastern & western horizon
corkscrew (to help discriminate between clockwise-upwards and counter clockwise-upwards
twisting - it's hard to think straight at 12,500 feet!)