Effect of shelterbelt structure on wind reduction and meteorological damage

The purpose of this study is to clarify the relationship between shelterbelt structure and the functions of wind reduction and snow break, and to determine measures to reduce the meteorological damages caused by wind force, and snow and ice load to natural shelterbelts. The results are summarized as follows: 1. Relationship between shelterbelt structure and the functions of wind reduction and snow break. In order to clarify the effects of the width and density of a shelterbelt on wind reduction, model wind experiments and field observations of wind speed distribution were carried out around shelterbelts with different widths (W) and total area densities (Ad). The values of Usub(m)/Usub(0) (minimum relative wind speed), Xsub(m) (distance of the minimum wind speed from the leeward edge of the shelterbelt), and d70 (shelter distance beyond which the wind speed U does not exceed 70% of Usub(0)) could not be accurately estimated using only the values of W or Ad. However, W x Ad, which is defined as the product of W and Ad, related to Usub(m)/Usub(0), Xsub(m), and d70, was found to be a useful index for a natural shelterbelt. In order to obtain field data on the snow break effect on shelterbelts, field observations were performed. In order to verify the validity of the model experiments on snow break forests, a wind tunnel experiment using an experimental wood model was conducted, and the results were compared with those obtained on the field. 2. Meteorological damages by wind force, and snow and ice load in natural shelterbelts. By analyzing the wind damage caused by Typhoon 200221 at the shelterbelts and the damage caused by glaze in the Japanese larch forest in Hidaka, Hokkaido, in February 2004, a susceptibility to windthrow and glaze damage was found and multiple regression models to predict the damage rate were obtained. The effect of tree height and slenderness ratio on wind resistance was found using a mechanistic model to assess the risk of wind and snow damage. Wind resistance increased with decreasing slenderness ratio and decreased with increasing tree height with no change in the slenderness ratio. However, the effect of tree height on wind resistance in the case of a higher slenderness ratio is smaller than that in a lower ratio.