Longleaf pines and other plants grow in an 8-foot tall open-top field chamber. Exposed to elevated levels of CO2, pines in the chamber grew faster than pines grown in ambient CO2. Image courtesy Barry Dorman, ARS.

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Elevated Carbon Dioxide Has Uneven Influence on Longleaf Communities

By Laura McGinnis
December 11, 2007

No plant is an island. That's one conclusion of a global change study conducted by Agricultural Research Service (ARS) scientists at the Soil Dynamics Research Unit in Auburn, Ala.

The researchers found that carbon-dioxide-induced changes to longleaf pine communities could lead to competitive displacement and the gradual elimination of species that currently thrive there.

Led by plant pathologist G. Brett Runion and plant physiologists Stephen A. Prior and Hugo H. Rogers, the team investigated the response of longleaf pine communities to the doubled atmospheric carbon dioxide (CO2) levels projected to occur within this century.

They compared the growth rates of longleaf pine and four southeastern plant species that often grow in the same environment after three years of exposure to either ambient or elevated CO2. Within the simulated plant communities, species responses varied significantly.

Longleaf pine savannas account for about 3.7 million acres of the southeastern United States—about 4 percent of their original range. However, they remain an influential part of the southeast landscape. The pines are highly resistant to many insects and diseases that harm other southeastern pines. Plus, longleaf communities support several endangered species, including red cockaded woodpeckers and gopher tortoises.

The scientists were surprised to observe that after three years, longleaf pines exposed to higher CO2 were more than five feet tall on average—nearly two feet taller than the control group.

The total biomass of the plants exposed to elevated CO2 was 70 percent greater aboveground and 49 percent greater belowground than that of the control. However, growth rates were not universal. While longleaf pines shot up, wiregrass, rattlebox and butterfly weed actually decreased in biomass, and sand post oak had no significant growth response.

These responses affected the plant community's composition. Longleaf pine accounted for 76 percent of the total biomass in ambient CO2 plots, but made up 88 percent of the elevated CO2 plots. Wiregrass, rattlebox and butterfly weed dropped from 19 percent of the ambient plots to 8 percent of the elevated CO2 plots.

ARS is the U.S. Department of Agriculture’s chief in-house scientific research agency.