THE DISTRIBUTION OF MOISTURE IN THE LIVING STEM IN SITKA SPRUCE AND DOUGLAS FIR

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Abstract
Equilibrium in the moisture content of the stem appears to be reached at a given percentage of saturation rather than at a percentage based on the dry weight, and this method of expressing moisture content eliminates many of the fluctuations apparent with the latter. Summer moisture content in Sitka spruce ( Picea sitcbensis, Carr. ) was highest on the site with the highest rainfall and lowest with the lowest rainfall. It decreased in late summer, suddenly in Sitka spruce (in August) and gradually in Douglas fir ( Pseudotsuga taxifolia Brit.). There was a sharp moisture gradient from cambium to heartwood, the saturated zone being very narrow except on the wet Sitka spruce site. In the Douglas fir it appeared that water could be withdrawn from the layers just behind the transpiration stream faster than it could be replaced, leaving this zone drier than the surrounding layers. Lateral root pruning in Douglas fir led to the drying out of a narrow strip of tissue in the stem.

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