ABRUPT GROWTH CHANGES IN NORWAY SPRUCE AND YEZO SPRUCE NEAR AN INDUSTRIAL DISTRICT IN HOKKAIDO, JAPAN

Increments in the radii of Norway spruce (Picea abies Karst.) and Yezo spruce (Picea jezoensis Carr.) trees that revealed symptoms of a decl ine in growth were analyzed by dendrochronological methods in an attem pt to correlate past reductions in growth with their main causes. The trees were growing at different sites near the industrial district of Tomakomai, Hokkaido. A skeleton plot method was used to construct a se ries of pointer years that revealed the number of trees with a clear r eduction in growth or recovery from such a reduction. An analysis of ' 'abrupt growth changes'' demonstrated that at least two periods of gro wth reduction were common to a large number of Norway spruce trees. Th e reduction events were related to the records of industrial activity near the forest and meteorological data. The growth reduction in the 1 970s coincided with the start of operation of certain local factories, and its extent was related to the distance from the industrial region . By contrast, a reduction in growth in 1984 was detected at all the N orway spruce sites and the extent was approximately the same at all si tes. This phenomenon was related to extreme drought conditions. Growth of Yezo spruce trees was less sensitive to industrial activity and to drought than that of Norway spruce. Thus, differences in response to air pollution and drought were observed between the two species.