On the Local Wind Distribution and the Wind Break Density in the Shari-Abashiri Region, Hokkaido

The total area of wind breaks reaches 37, 629 ha in Hokkaido in 1969. In order to rearrange the wind breaks, it was hoped to study the distribution and the density of wind breaks in relation to local wind conditions. Here, an example of the studies in the Shari-Abashiri region is reported. The writers made firstly investigations into the density and the prevailing directions of wind breaks through interpretation of air photos and secondly field observations of wind-shaped trees, such as Larix leptolepis, Fraxinus mandshurica and Populus spp., as an indicator of the local wind conditions. The following results, as given in the figures attached, were obtained: The Shari-Abashiri region studied can be divided into three from the viewpoint of wind conditions. They are; i) the northern foot region of Mt. Shari, ii) the coastal region and the marshy region along the Shari River, and iii) the hilly region between the cities, Koshimizu and Kiyosato. The characteristics of each regions are: In the first region, the density of wind breaks is 100m/ha on the average with the maximum 150-200m/ha. The southeasterly winds prevail up to 100m above sea level on the foot as called “Sharidake-oroshi (fallwind from the Mt. Shari)”, which blows especially in spring. The direction of the wind breaks are mainly from SW to NE. In the second region, the density of wind breaks is lower than 25m/ha. This coastal region is lower than 20m above sea level and has 2-3km width. There prevail the northerly winds from the Sea of Okhotsk. Where the marshy, low land extends 8-10km inland from the coast, the northerly winds invade into there. In the third region, the density of wind breaks is mainly 50-75m/ha. Almost all wind breaks run in W-E direction. The prevailing wind directions are southerly, but northerly in an exceptional year with cool summer, like in 1971.