Abstract:In order to investigate the cause of forest decline, the field measurements of hydroperoxides and ozone were performed in declined defoliate forest located at Sirane Mountain in Oku-niko and red pine forest located at Oshiba-altiplano in Nagano. The exposure experiments to 50′10-9 O3, 100′10-9 O3 and mixture of 50′10-9 O3 + 2′10-9~3′10-9 peroxides on Beech and Birch were also conducted in outdoor chambers. The results of field measurements showed that there was no significant different in average concentrations of O3 between in Oku-niko and Nagano, however the average concentrations of hydrogen peroxide and methl hydroperoxide were higher in Oku-niko forest than that in Nagano. Atmospheric hydroperoxides always coexisted with O3, and its concentrations increased with rising O3 concentrations both in two site. The exposure experiments showed that different foliar injury symptoms from O3 induced were observed on Beech and birch exposed to 50′10-9 O3 + peroxides. Compared with 100′10-9 O3, 50′10-9O3 coupling with 2′10-9~3′10-9 peroxides induced more severe foliar injuries and greatly decrease in net photosynthetic rates. These results indicate that the mixture of O3 and peroxides were more responsible to the decline of wild forests than that of O3.