predicting the impacts of future high atmospheric co2 concentration, [co2], on the physiology and growth of boreal forests is complicated by interactions of co2 with other environmental conditions. two-factor co2 x environment interactions on boreal tree species have been reported. this research was designed to determine how photosynthetic and growth responses of white birch (betula papyrifera marsh.) to elevated [co2] are influenced by multifactor interactions of other environmental factors.