Stem Form of Young Larix As Influenced by Wind and Pruning
Abstract:Four-year-old Larix laricina trees, pruned to different intensities, were exposed to unidirectional and multidirectional winds from oscillating electric fans. Stem form, as measured by the distribution of the annual increments along the bole, is largely determined by the size and vigor of the live crown. Removal of live crown by drastic pruning favored growth of the upper stem and decreased growth on the lower stem, whereas exposure to wind caused a pronounced downward shift of increment towards the stem base, usually at the expense of upper stem parts. Prevention of wind sway by staying the trees largely eliminated the downward shift of increment. Height growth of free-swaying trees was also reduced, and this reduction was partially offset by staying. Trees responded to unilateral winds by producing eccentric growth on the lower stem consisting of a high proportion of reaction wood. However, the increased increment on the lower bole of trees exposed to multilateral wind consisted of wood of normal structure uniformly distributed circumferentially. On the basis of results obtained in this study, the physiological development of stem form was divided into two components. "Passive" distribution may be considered as the persistent tendency for growth to concentrate on the upper portion of the stem, and "stimulatory" distribution as the tendency for growth to be preferentially distributed to stem regions experiencing physical stress. The arguments favoring this separation are discussed.
Document Type: Journal Article
Affiliations: Principal Plant Physiologist with the Lake States Forest Expt. Sta., Forest Service, U. S. Dept. Agric.
Publication date: December 1, 1965
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