, Volume 19, Issue 1, pp 58-65

The influence of wind on branch characteristics of Pinus radiata

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Abstract

Measurements taken from trees growing in exposed and sheltered areas within two structurally similar forests were used to investigate the influence of wind on branch characteristics of mature New Zealand-grown Pinus radiata. A widely used branch model was used to remove the influence of treatment and site differences in tree stem diameter and height, so that the influence of wind on branch diameter could be examined. At site 1 average windspeed in the exposed treatment exceeded average windspeed in the sheltered treatment by 62%. When averaged across sites, mean branch diameter, branch index (mean diameter of the largest branch, in each of the four azimuthal quadrants) and largest branch diameter in exposed areas significantly exceeded values for trees in sheltered areas by 9 mm (25%), 42 mm (54%), and 72 mm (72%), respectively. Treatment and site differences in tree stem diameter and height partially accounted for the observed increases in branch diameter. However, after these effects were removed by the model, branch diameter in exposed areas still significantly exceeded that in sheltered areas by 21 mm for branch index and 44 mm for the largest branch. Treatment and site variation in this residual branch diameter was almost entirely attributable to topographical exposure to 1 km, a variable which has been found to be strongly correlated to windspeed. Possible reasons for these observed wind-induced increases in branch diameter are discussed.