In Mt. Taisetsu the forest limit was not dependent upon Kira's Warmth Index (WI) 15 but was controlled by either the prevailing wind or development of soillayer. The prevailing north-westerly wind in winter caused lowering of altitude of forest limit rather than WI15 altitude, possibly because it produced dehydrate-dessication damage in the winter buds of trees of the forest limit. Altitude of the forest limit was not necessarily related to the absolute altitudes of ridge but to the distance between the main ridge on a slope forming the forest limit and forest limit itself. Trees hardly grew in the boulder fields, which seemed to be formed by periglaciation activities in the palaeoclimatic conditions and contained a slight soil layer. The forest limit in the boulder fields descended lower than the level expected when a soil layer is present.
