| In highway snowbreak woods that have grown to maturity、 the branches of adjacent trees overlap and the leaves shade each other. This causes branches near the ground to die. Such dying allows snow to penetrate through the woods、 which reduces visibility on the road. To prevent low branches from dying、 stand thinning at the appropriate time is necessary. However、 such thinning reduces tree density、 which raises concerns about temporary reductions in visibility improvement. Because of this concern、 there are highway snowbreak woods that have not been properly thinned. [*][*]To examine the relationship between the tree density of highway snowbreak woods and the visibility improvement they afford、 the authors conducted field surveys and wind tunnel tests. From those surveys and tests、 the minimum tree density that maintains visibility improvement was determined.[*][*]The study found the following:[*]1) Highway snowbreak woods improve visibility under snowstorm conditions.[*]2) The tree density of a snowbreak woods greatly influences the visibility improvement afforded by the woods.[*]3) Leaf-area index influences visibility improvement.[*]4) To improve visibility、 the tree density for a 32-m-wide snowbreak woods should be at least 400 trees per hectare. |
