Formation of Wind-shaped Trees in Rishirito-island, Hokkaido

Abstract

In the mountain district wind-shaped trees constitute typical climatic landscapes and they are regarded as effective indicators of the winds. But, there are some disagreements between the theories of their origin. The author attempts to clarify what agencies act on wind-shaped trees.Some investigations are made in Rishirito-island which has an isolated mountain in the Hokkaido district and following facts are found. (A) The distribution of wind-shaped deciduous broad-leaved trees, birches and alders etc., suggests that southwesterly winds blow toward the mountain and become separate to its both sides (fig. 2). On the other hand, the distribution of wind-shaped evergreen conifers, white and silver fir, suggests that winds diverge, and also blow into the coast and blow down on the mountainside (fig. 3). (B) On the Sea of Okhotsk temperature inversions in the lower layer often appear in Spring and Summer, and they affect the distribution of winds in Rishiritoisland significantly. In the period of stable stratification (May-August), generally, southwesterly winds that blow against the mountain, diverge to its northwestern and southeastern side. And the winds stagnate in the windward, blow through the both sides, and blow gently in the leeward. While in the period of unstable stratification (October-March), generally, the westerly strong winds blow on anywhere but the leeward (fig. 5).Then, examining characteristics of the distributions of winds that agree with the distributions of wind-shaped trees, the author concludes that wind-shaped trees in Rishirito-island are formed in the following way. In the case of deciduous broad-leaved trees, they are deformed by the southwesterly winds that prevail in the period of stable stratification. In the case of evergreen conifers, they are deformed by the same southwesterly winds as in the former case, and in the limited area they are deformed by the salt breezes that prevail in the period of unstable stratification. Hereafter it is essential to find out another agency that forms wind-shaped trees.