八ケ岳亜高山樹林の縞枯の成因 : I.その分布と卓越風との関係
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概要
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1. The distribution and chief direction of "dead tree strips" in the subalpine coniferous forest of Abies Veitchii and A. Mariesii were surveyed in the northern part of the Yatsugatake Mountains, Nagano Prefecture, and they were discussed in relation to the direction and velocity of prevailing wind. 2. Many "stepped" Abies-forests, the shifting areas of "dead tree strips", were observed at the subalpine climax forest in high altitude above 2100m., especially along the western edges of mountain ridges facing valleys, whose direction was southwest or west, or along the western edges of mountain spurs, direction of which was almost in right angle with the valleys. 3. The local directions of prevailing wind, which were determined by the deformation of Abies crowns, are mostly in right angle with mountain ridges or spurs, and are parallel to the direction of valleys. The wind directions in the "stepped" Abies-forest area are limited in SE-SW-NW, and the highest frequency was found in SW-direction. 4. The observed direction of prevailing wind was discussed on the basis of aerological and meteorological information ; the direction and velocity of prevailing winds are a resultant of upper prevailing westerlies (strongest in winter) and of valley breezes (strongest in summer), which often develops on western mountain slopes, in the northern part of the Yatsugatake by the effect of topographic conditions. 5. The developing shift of "dead tree strips" occurs in the same direction as that of the prevailing wind. 6. The wind velocities at each part of mountains were discussed based on the aerological and meterological information, and it was found out that a close relationship between distribution of wind velocity and that of "dead tree strips". The wind velocity at the exposed slope and mountain top near the "dead trees strips" could be estimated at 10-12m./sec. in annual mean.