Seasonal variations of the physical environment of larch forest which is the representative artificial forest in Nagano Prefecture were observed aiming at clarifying the forest influence to its environment.
The variations are closely related to the state of foliation. Namely, the max. value of albedo was ca. 18 percent in the last ten days of October reflecting the autumn tint and that of the radiation under the canopy was ca. 45 percent in the open in winter because of the defoliation. Canopies thus play the important role of mulch to the forest floor as far as thermal phenomena are concerned. As the result, the max. and min. temperatures of soil surface under the trees showed marked falls of ca. 30°C and 3°C respectively than those of the bare soil block in midsummer because of the existence of larch forest which reduces the amplitude of soil temperature fluctuation. Air temperature in the larch forest was also reduced in summer by 7.5°C to offer a cool atmosphere to its environment. The main portion to absorb solar energy moves vertically in the stand according to the foliation and defoliation processes which is reflected in the seasonal variations of the vertical distribution of air temperature in the forest. Energy balance analysis made it clear that one of the greatest forest influences was heat transfer through latent heat flux, namely, the larch forest controls Bowen's ratio to provide a cool and fresh atmosphere to its surrounding. It should be emphasised that such a heat exchange is almost lacking in the bare soil, asphalt and concrete in urban areas.