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No. 118: Jul-Aug 1998

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Lunacy In Trees

More than a half-century ago, Yale biologist H.S. Burr inserted electrodes into trees and found that the voltages between them varied with the phase of the moon. (Ref. 1)

The influence of the moon upon trees is even more palpable: the diameters of tree stems also bloat and shrink with the position of the moon in the sky. There is a tide in the affairs of trees, it seems. If tides occur twice a day, so do the swellings and shrinkings of trees.

These tidal patterns are evident even when the trees are kept in darkness and at constant pressure and humidity. Even more surprising, chunks of tree stems that are sealed to prevent water from flowing in or out will still expand and contract according to the 24-hour, 49-minute lunar cycle as long as the cambium, the most active growing region, survives.

The dimensional changes are small -- only tenths of a millimeter, but even these seem too large, given the weakness of the moon's gravitational field here on earth. (Ref. 2 and 3)


1. Burr, H.S.; "Moon Madness," Yale Journal of Biology and Medicine, 19:249, 1944.
2. Zurcher, Ernst, and Cantiana, MariaGiulia; "Tree Stem Diameters Fluctuate with Tide," Nature, 392:665, 1998.)
3. Milius, S.; "Tree Trunks Swell in Synchrony with Tides," Science News, 153:245, 1998.)

Tree-stem diameter (Top) Tree-stem diameter. Ordinate scale marks are 0.04 millimeters apart. (Bottom) Todal force. Ordinate scale marks are 20 milligals apart.

From Science Frontiers #118, JUL-AUG 1998. 1998-2000 William R. Corliss