Evaluating Possible Causes for the Decline of Japanese Fir (Abies firma) Forests Based on δ13C Records of Annual Growth Rings

Abstract

Marked damage to Japanese fir (Abies firma) forests have been observed on Mt. Oyama, Tanzawa Mountains, Japan, which is located close to densely populated and heavily industrial areas, since the 1960s. The authors evaluated possible causes for the decline based on the {delta}{sup 13}C records of annual growth rings sampled from trees without visual decline symptoms. For comparison, the {delta}{sup 13}C records for Japanese Cedar (Cryptomeria japonica) on Mt. Oyama for which decline has not been observed were also investigated. The results showed that the {delta}{sup 13}C of rings from both tree species increased abruptly during the 1960s and then decreased after reaching a maximum value in the early 1970s, while the tree growth inversely changed with {delta}{sup 13}C. The historical changes of {delta}{sup 13}C of rings and tree growth were correlated with atmospheric SO{sub 2} concentrations with a delay of 5--10 years in their maximum responses. Exposure to SO{sub 2} at the levels estimated during the 1960s on Mt. Oyama can induce the increase of {delta}{sup 13}C of rings and the reduction of tree growth with stomatal closure being the probable cause. Previous studies have shown that Japanese fir has a lower tolerance to SO{sub 2} as compared tomore » Japanese cedar. These results suggest that the fir forests on Mt. Oyama were injured mainly by SO{sub 2} pollution during the 1960s causing the decline.« less