Zombie Tree Branches
clever...@gmail.com
A couple of years ago I posted about conifer tree branches that “come alive” after they die and shed their needles. Of course they’re not really still alive, but they move autonomously more than they did when alive. Here are two side-by-side pictures of the same black spruce tree.
The photo on the left, with the branches curving downward to the point of forming a semicircle, was taken May 12 when the temp hit 90 degrees and the RH 13%. The photo on the right, with the straightened branches, was taken 5 days later when the high temp was 49 degrees and the low RH 85%. I first noticed this phenomenon when I’d build a trail and cut all the branches above head height, then came back on a dry, warm day and get hit in the head and face with dead branches.
Apparently this is due to the types of wood laid down as branches grow. The wood on the underside has to be stronger to resist gravity, snow piled on the branch and other forces, and is called “resistant wood.” This wood is more responsive to moisture changes than the wood topside of the branch. When the air becomes dry, the reaction wood on the underside of the branch loses moisture and contracts more than the wood on the topside, causing the branch to curve downward. In humid conditions, the underside absorbs more moisture and expands, which causes the branch to reverse the process and become straighter. A still-living branch is supplied with moisture from the tree and doesn’t suffer this extreme moisture differential between the two types of wood in a branch, so doesn’t move like this, or at least to nearly this degree.
Steve Wilson
Isabella
Al Stoops
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