Elevated atmospheric CO2 stimulates aboveground biomass in a fire-regenerated scrub-oak ecosystem

The effect of elevated atmospheric CO2 concentration (C-a) on the aboveground biomass of three oak species, Quercus myrtifolia, Q. geminata, and Q. chapmanii, was estimated nondestructively using allometric relationships between stem diameter and aboveground biomass after four years of experimental treatment in a naturally fire-regenerated scrub-oak ecosystem. After burning a stand of scrub-oak vegetation, re-growing plants were exposed to either current ambient (379 muL L-1 CO2) or elevated (704 muL L-1 CO2) C-a in 16 open-top chambers over a four-year period, and measurements of stem diameter were carried out annually on all oak shoots within each chamber. Elevated C,, significantly increased aboveground biomass, expressed either per unit ground area or per shoot; elevated C. had no effect on shoot density. The relative effect of elevated Ca on aboveground biomass increased each year of the study from 44% (May 96-Jan 97), to 55% (Jan 97-Jan 98), 66% (Jan 98-Jan 99), and 75% (Jan 99-Jan 00). The effect of elevated C-a was species specific: elevated C-a significantly increased aboveground biomass of the dominant species, Q. myrtifolia, and tended to increase aboveground biomass of Q. chapmanii, but had no effect on aboveground biomass of the subdominant, Q. geminata. These results show that rising atmospheric CO2 has the potential to stimulate aboveground biomass production in ecosystems dominated by woody species, and that species-specific growth responses could, in the long term, alter the composition of the scrub-oak community.