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William C. Ashby
Harold C. Fritts

A multivariate technique was employed to assess tree-ring growth and climatic relationships of white oak in northern Illinois-Indiana, including LaPorte, Ind. Climate accounted for 59% of the variance in ring-width chronology, and prior growth accounted for 2%. Since the reported LaPorte precipitation anomaly is considered to be largely a phenomenon of summer convective storms (Changnon, 1968), the importance of the late spring and summer precipitation on ring width suggests that white oak rings from the LaPorte stands versus the control stands would be likely to show differences in growth after 1930 if a precipitation anomaly had occurred.

Our particular tree-ring analysis neither proves nor disproves the precipitation anomaly at LaPorte. It does suggest that some factor in the LaPorte area became increasingly more limiting to tree growth than climate during the decade of 1940, and caused a gradual reduction of growth. Our best inference is that this growth reduction may have been a direct result of toxic effects from severe air pollution correlated with high levels of smoke-haze in Chicago during the decade of the 1940s. This would suggest that rings from trees in other urban areas should be studied, as they may contain a record of past air pollution or, in the absence of pollution and other effects resulting from disturbance by man, may be suitable for documentation of anomalies in climate.

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