Ecophysiological Responses of Northern Birch Forests to the Changing Atmospheric CO2 and O3 Concentrations

Abstract

The effects on birch (Betula spp.) of elevated carbon dioxide (CO 2 ) and ozone (O 3 ), which are both increasing in the troposphere, are surveyed in detail based on the literature. Birches establish themselves in the open field after disturbances, and then become dominant trees in temperate or boreal forests. Ecophysiological approaches include the measurement of photosynthesis, biomass, growth, and survival of seedlings and trees. Elevated CO 2 levels give rise to a net enhancement of the growth of birch trees, whereas high O 3 generally reduces growth. Although the effects of the two are opposed, there is also an interactive effect. Basic physiological responses of the single genus Betula to CO 2 and O 3 are set out, and some data are summarized regarding ecological interactions between trees, or between trees and other organisms.