PARENT SESSION
Oral Session #53: Elevated CO₂: Communities, ecosystems, soils.
Presiding: G. Lin
Wednesday, August 7. 8:00 AM to 11:30 AM. Coconino Meeting Room, TCC.

Increased aboveground biomass in elevated CO₂ masks species-specific growth responses in a scrub-oak ecosystem.

Anderson, Hans^*,1, Hymus, Graham¹, Hinkle, C Ross², Drake, Bert¹, ¹ Smithsonian Environmental Research Center, Edgewater, MD² Dynamac Corporation, Kennedy Space Center, Fl

ABSTRACT- We report the effect of elevated atmospheric CO₂ concentration (C_a) on aboveground biomass of three Oak species. The plants had grown for six years in a natural ecosystem, in open top chambers maintained at either current ambient or elevated (current ambient +350 ppm) C_a. The study on Merritt Island, Florida, is one of few long-term investigations of the effects of elevated C_a on a native woody ecosystem. After six years aboveground biomass in the elevated chambers contained 1200 g C m^-2 compared to 700 g C m^-2 in the ambient, a 58% increase. During the first four years of the study the stimulation of above ground biomass in elevated CO₂ increased consistently from 40% to 80%. Contrasting this, the stimulation has decreased in the last two years, most likely an indication of a temporary or permanent limitation to growth. The growth of three oak species that combined constitute over 80% of aboveground biomass in this ecosystem, differed in response to growth in elevated C_a. Two, Quercus myrtifolia and Quercus chapmanii, responded strongly, while the third, Quercus geminata was unaffected by growth in elevated C_a. The species-specific response appears to be resulting in a shift in species composition. Q. geminata has increased as a proportion of total aboveground biomass in the ambient treatment, but not in the elevated treatment. For this ecosystem, accumulation of aboveground biomass after fire has been more rapid in elevated C_a. When combined with the possibility of changes in ecosystem species composition, elevated C_a may have important implications for this fire-dependent ecosystem.

KEY WORDS: elevated co2, native ecosystem, growth, oak species