A Study in Characteristics of the Forest in Farmyard and its Relation to Prevailing Winds in the lzumo Plain

Abstract

Forests in farmyard are located and called Tsuiji-matsu in the Izumo Plain, Shimane Prefecture. The purpose of this paper is to examine an effect of these forests against the winds, and to consider the distribution of local winds suggested by arrangement of forests. Most of the Tsuiji-matsu forest is composed mainly of well-trimmed trees of Pinus thunbergii which stand 5 to 7 metres tall around every house, and lower trees of Machilus thunbergii, Castanopsis cuspidata, Phyllostachys spp., Cyclobalanopsis spp. etc. are planted subsidiarily to them. Meteorologicai observations resulted in the fact that these forests made the wind speeds decrease to a third during winter. The directions of the prevailing wind were measured at 189 points in the Plain on the basis of arrangement of Tsuiji-matsu forests. Available meteorological data at several stations show that these directions are closely correlated with the strongest winds during the winter. This means that the Tsuiji-matsu forests indicate the directions of the local prevailing winds during the winter. They are illustrate in Fig. 6. Important facts revealed in this study are summerized as follows : 1) Two different winds during the winter are observed this study area ; W to NW winds from the Taisha Bay, west to the Plain and NW winds from the Uppurui Inlet northwest. This is explained that the Kitayama Mountains exceeding 500 metres in altitude northwest to the Plain offers an obstacle against the winds. 2) These two winds join at the eastern part of the Plain, where the average wind speeds becomes stronger. 3) In southernmost Plain S winds prevail during the summer though W winds prevail during winter.