The impact of tropospheric ozone on landscape-level merchantable biomass and ecosystem carbon in Canadian forests

Studies have shown that tropospheric ozone (O-3) impacts trees in various ways, including growth reductions. To date, the landscape-level response of Canadian forests carbon (C) to O-3 exposure has not been quantified. We used a modified version of the Carbon Budget Model of the Canadian Forest Sector and data from Aspen FACE to quantify the landscape-level impacts of different O-3 exposure modelling experiments. The main strengths of our approach consisted of using the most complete empirical data available to estimate the amount and location of forest C across Canada, as well as explicitly simulating the consequences of fire, insect, and harvest disturbances on forest C dynamics. These disturbances lead to younger forests and, considering trees sensitivity to O-3 exposure to decrease with age, thus result in higher landscape-level modelled impacts for the same O-3 levels. Despite various sources of uncertainty, our results indicate that even under a modelling experiment where O-3 increases continuously over four decades, the landscape-level impacts on the merchantable biomass and ecosystem C remain limited. Our results also suggest that the current direct impacts of O-3 on Canadian forests are likely below detection at the landscape level.