Stem Form of Young Larix As Influenced by Wind and Pruning

Abstract

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 vigorof 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 windsway 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 proportionof 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 intotwo 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 argumentsfavoring this separation are discussed.