Consequences of elevated levels of amospheric CO₂ and O₃ for growth of Poplus tremuloides clones: the role of competition

Abstract

Concomitant increases in atmospheric CO₂ and 0₃ are expected to impact temperate forest ecosystems. Free air CO₂ and 0₃ enrichment (FACE) was used to examine the interactive effects of these gases on shoot growth responses of quaking aspen grown in an experimental system (FACTS-II, Aspen FACE) in northern Wisconsin. A central goal was to examine how the interactions of atmospheric treatments and genotype impact competitive relations among genotypes. Several aspen clones with differing sensitivities to CO₂ and 0₃ were planted in randomized mixtures within half of each 30 m diameter FACE ring, with 3 replications of each combination of low and high levels of CO₂ (ambient and 56 Pa) and 0₃ (ambient and 1.5xambient). We hypothesized that several factors, apart from atmospheric treatments, will have strong effects on individual tree growth in this system, such as genotypic potential, initial size, and competitive status. We non-destructively measured tree size and estimated annual biomass increments. A competitive index for each individual tree at the beginning of the growth interval was calculated using the ratio of its size to the average size of adjacent neighbors. We tested treatment effects using initial size as a covariate and competitive index divided into representative categories was evaluated as a class variable nested within clone. In 1998, effects of CO₂,0₃ and their interaction were not significant, but O₃xclone and O₃xcompetitive index interactions were significant. In 1999, CO₂xO₃xcompetitive index interactions were highly significant, so we tested treatment effects within competitive index categories where individuals are competitively disadvantaged, neutral or advantaged in terms of size relative to thek neighbors. Main effects and interactions of CO₂ and O₃ became larger and more significant as competitive index increase. At high competitive indices, elevated CO2 increased net growth in 1999 by 29% (p

Citation

McDonald, Evan P.; Kruger, E. L.; Riemenschneider, Don E.; Isebrands, J. G. 2001. Consequences of elevated levels of amospheric CO₂ and O₃ for growth of Poplus tremuloides clones: the role of competition. Air Pollution, Global Change and Forest in the New Millennium. p. 58. (2001)