Tropospheric O-3 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project Academic Article uri icon


  • 1. The impacts of elevated atmospheric CO2 and/or O3 have been examined over 4 years using an open-air exposure system in an aggrading northern temperate forest containing two different functional groups (the indeterminate, pioneer, O3-sensitive species Trembling Aspen, Populus tremuloides and Paper Birch, Betula papyrifera, and the determinate, late successionati O3-tolerant species Sugar Maple, Acer saccharum). 2. The responses to these interacting greenhouse gases have been remarkably consistent in pure Aspen stands and in mixed Aspen/Birch and Aspen/Maple stands, from leaf to ecosystem level, for O3-tolerant as well as O3-sensitive genotypes and across various trophic levels. These two gases act in opposing ways, and even at low concentrations (1.5 x ambient, with ambient averaging 34-36 nL L-1 during the summer daylight hours), O3 offsets or moderates the responses induced by elevated CO2. 3. After 3 years of exposure to 560 mol mol-1 CO2, the above-ground volume of Aspen stands was 40% above those grown at ambient CO2, and there was no indication of a diminishing growth trend. In contrast, O3 at 1.5 x ambient completely offset the growth enhancement by CO2, both for O3-sensitive and O3-tolerant clones. Implications of this finding for carbon sequestration, plantations to reduce excess CO2, and global models of forest productivity and climate change are presented.

published proceedings


altmetric score

  • 3

author list (cited authors)

  • Karnosky, D. F., Zak, D. R., Pregitzer, K. S., Awmack, C. S., Bockheim, J. G., Dickson, R. E., ... Isebrands, J. G.

citation count

  • 251

complete list of authors

  • Karnosky, DF||Zak, DR||Pregitzer, KS||Awmack, CS||Bockheim, JG||Dickson, RE||Hendrey, GR||Host, GE||King, JS||Kopper, BJ||Kruger, EL||Kubiske, ME||Lindroth, RL||Mattson, WJ||Mcdonald, EP||Noormets, A||Oksanen, E||Parsons, WFJ||Percy, KE||Podila, GK||Riemenschneider, DE||Sharma, P||Thakur, R||Sôber, A||Sôber, J||Jones, WS||Anttonen, S||Vapaavuori, E||Mankovska, B||Heilman, W||Isebrands, JG

publication date

  • June 2003