The effect of wind sway on the form and development of Pinus radiata D. Don

Abstract

The average growth of four series of trees of Pinus radiata D. Don, which were prevented from swaying in the wind by the attachment of guy-wires, is compared with the average growth of similar series of free-swaying trees.

Free-swaying trees grew more in diameter over the lower part of the trunk than stayed trees. After 10 yr the increased growth due to sway could be detected to a height on the trunk of between 25 and 30 ft. The effect of sway at a height of 4 f t was greater in a very heavily thinned test area than in a well-stocked test area. Sway caused increased diameter growth of roots near the trunk and increased eccentric trunk development along the line of the main winds. The height growth of the stayed trees was little different from that of the free-swaying trees, but height/diameter relationships were changed. After 2 yr trees that had been prevented from swaying were no longer stable in a normal environment.

When the upper parts of stayed trees were allowed to sway the trees made good use of the factors of the locality for 8 yr. In a series where stayed trees were prevented from swaying throughout their length progressive suppression of diameter and volume increment was observed over 15 yr. Individual reaction to the stimulus of sway appeared to be one of the factors that contributed to the progressive assertion of dominance by certain trees.