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Effects of Elevated CO2 on Plant-Insect Interactions in a Scrub-Oak Forest
Stiling, P., Moon, D.C., Hunter, M.D., Colson, J., Rossi, A.M., Hymus, G.J. and Drake, B.G.  2002.  Elevated CO2 lowers relative and absolute herbivore density across all species of a scrub-oak forest.  Oecologia DOI 10.1007/s00442-002-1075-5.

What was done
The authors studied the effects of an approximate doubling of the air's CO2 concentration on a number of characteristics of several insect herbivores feeding on plants native to a scrub-oak forest ecosystem at the Kennedy Space Center, Florida, USA, in eight ambient and eight CO2-enriched open-top chambers, where five species accounted for over 98% of the total plant biomass per chamber.

What was learned
In the words of the authors, the "relative levels of damage by the two most common herbivore guilds, leaf-mining moths and leaf-chewers (primarily larval lepidopterans and grasshoppers), were significantly lower in elevated CO2 than in ambient CO2, for all five plant species," and "the response to elevated CO2 was the same across all plant species."  Also, they report that "more host-plant induced mortality was found for all miners on all plants in elevated CO2 than in ambient CO2."  These effects were so powerful, in fact, that in addition to the relative densities of insect herbivores being reduced in the CO2-enriched chambers, and "even though there were more leaves of most plant species in the elevated CO2 chambers," the total densities of leaf miners in the high-CO2 chambers were also lower for all plant species.

What it means
In a higher CO2 world of the future, earth's natural ecosystems may be able to better withstand the onslaughts of various insect pests that have plagued them in the past.  An interesting implication of this finding, as the authors note, is that "reductions in herbivore loads in elevated CO2 could boost plant growth beyond what might be expected based on pure plant responses to elevated CO2 [our italics]," which is a truly exciting observation.

Reviewed 4 December 2002