Abstract
A method for assessing the influences of air pollution on tree ring growth was presented. The annual increment growth of 270 Japanese Cedars, growing at 51 sites in a rural area of Fukui Prefecture, was determined from the soft X-ray films of increment cores (5 mm diameter). Ring indices were calculated to normalize the trends in ring widths with tree age, by fitting each measured series of ring widths to an exponential curve. Stepwise multiple regression technique was used to analyze the relationships between ring indices and seasonal climatic conditions. During the period with no significant air pollution, combined meteorological elements accounted for about 70% of the variance in ring-width chronology. Further normalization, i. e., calculation of standardized ring index (SRI), was carried out by multiple regression analysis to minimize the fluctuations in ring indices due to climatic variations.
From 1931 to 1971 the mean value of SRI fluctuated in a narrow range i. e., about 0.8-1.2, but once a thermoelectric power station has started the operation in September 1972, rapid decrease of SRI has been observed and the minimum value (0.54) was recorded in 1976. Emission of SO2 gas from the power station was reduced since July, 1975 when a scrubber system was installed to the power station. The partial recovery of SRI observed since 1976 suggested the subsequent improvement of ambient air quality. A close association was confirmed between the significance of growth inhibition, evaluated by SRI, and the distance from the power stations.
