A Case Study of Risk Assessment of Ozone Impact on Forest Tree Species in Japan

Ozone (<TEX>O₃</TEX>) is a main component of photochemical oxidants and a phytotoxic air pollutant. Although the current levels of tropospheric <TEX>O₃</TEX> in East Asia could adversely affect productivity of forest tree species, risk assessments of <TEX>O₃</TEX> impact were limited. In this paper, we summarize the methodology of risk assessment of <TEX>O₃</TEX> on forest tree species based on our two previous studies, risk assessments of <TEX>O₃</TEX> impact on the growth of Fagus crenata by Watanabe et al. (2012) and on the annual carbon absorption of three representative conifers, Cryptomeria japonica, Pinus densiflora and Larix kaempferi by Watanabe et al. (2010). <TEX>O₃</TEX> sensitivity of each tree species obtained from an experimental study, <TEX>O₃</TEX> exposure and atmospheric N deposition based on field monitoring and vegetation survey were integrated by geographic information system method. Based on the results, we conclude that the area with high risk of <TEX>O₃</TEX> impact does not necessarily correspond to the area with high <TEX>O₃</TEX> exposure. The varieties of tree habitat, tree sensitivity to <TEX>O₃</TEX> and annual carbon absorption among the tree species, and N deposition-induced change in the <TEX>O₃</TEX> sensitivity of F. crenata are raised as the factors of discordance between areas with high risk and those with high <TEX>O₃</TEX> exposure. In the last part of this paper, we discuss the present uncertainty and perspectives of risk assessment for the future studies on the impact of <TEX>O₃</TEX> on forest tree species in East Asia.