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Leaf-Galls and Leaf-Mines of Mature Oak Trees
Reference
Kampichler, C., Teschner, M., Klein, S. and Korner, C. 2008. Effects of 4 years of CO2 enrichment on the abundance of leaf-galls and leaf-mines in mature oaks. Acta Oecologica 34: 139-146.

Background
The authors write that "since CO2 enrichment alters the composition of live plant tissues, the ongoing global increase of atmospheric CO2 concentration is expected to affect plant-animal interactions," but that "systems studied so far have not included mature trees," which deficiency they attempted to remedy with their new experiment.

What was done
Kampichler et al. "determined the abundance of dominant leaf-galls (spangle-galls induced by the cynipid wasps Neuroterus quercusbaccarum and N. numismalis) and leaf-mines (caused by the larvae of the moth Tischeria ekebladella) on freely colonized large oaks in a mixed forest in Switzerland, which received CO2 enrichment [540 ppm vs. 375 ppm during daylight hours] from 2001 to 2004" by means of "the Swiss Canopy Crane (SCC) and a new CO2 enrichment technique (web-FACE)" in a forest that they say "is 80-120 years old with a canopy height of 32-38 m, consisting of seven deciduous and four coniferous species."

What was learned
The German, Mexican and Swiss researchers report that although elevated CO2 reduced various leaf parameters (water content, proteins, non-structural carbohydrates, tannins, etc.) at the SCC site, "on the long term, their load with cynipid spangle-galls and leaf-mines of T. ekebladella was not distinguishable from that in oaks exposed to ambient CO2 after 4 years of treatment."

What it means
Whereas speculation has run rampant over the years about the long-term effects of atmospheric CO2 enrichment on plant foliage and its subsequent effects on animals of various trophic levels, Kampichler et al. conclude that in the situation they investigated, "CO2 enrichment had no lasting effect in all three [animal] taxa, despite the substantial and consistent change in leaf chemistry of oak due to growth in elevated CO2."

Reviewed 29 October 2008