PARENT SESSION
Oral Session #106: Plant Ecology: Global Climate Change.
Presiding: D. Breshears
Friday, August 9. 9:00 AM to 12:00 PM. Grand Ballroom East, Radisson.
Competition and growth in aggrading aspen stands exposed to elevated CO2 and tropospheric ozone.
MCDONALD, EVAN*,1, KRUGER, ERIC2, ISEBRANDS, JUD1, 1 USDA-Forest Service, Rhinelander, WI2 University of Wisconsin-Madison, Madison, WI
ABSTRACT- Rising levels of atmospheric CO2 and O3 may have antagonistic effects on northern temperate forests. The Aspen-FACE experiment in Northern Wisconsin addresses the interacting effects of elevated CO2 and O3 on aggrading stands of trembling aspen (Populus tremuloides). In a replicated block design (n = 3), 30 m diameter FACE rings containing a mixture of 5 aspen clones received the 2×2 factorial of ambient and elevated (+20 Pa) CO2 and ambient and elevated (1.5 × ambient) O3 treatments during growing seasons since 1998. Competition will likely influence tree growth response to atmospheric change. During stand development, we studied annual growth responses of individual trees in relation to an index of competitive standing (CS) that quantified relative height differences among neighboring trees. Treatment effects varied substantially among years, but average responses over 4 years show that atmospheric treatment effects were clone dependent and further modulated by CS. Generally, elevated CO2 enhanced growth for all clones, with the magnitude of enhancement influenced by CS, O3 level, and clone. However, O3 effects were more variable, in that both the magnitude and direction of O3 effects on growth depended on clone. Regarding treatment effects on competitive outcomes, treatments did not significantly alter competitive rankings among clones, and the relative growth increment assessed for each clone under competitively neutral conditions (i.e. no competitive advantage or disadvantage relative to neighbors) was a strong predictor of competitive potential.
KEY WORDS: FACE, competitive interactions, global change, Populus tremuloides