Elevated levels of tropospheric ozone (O3) are known to be detrimental to many plants and the pests that live on them, but with future increases in atmospheric CO2 can we expect ozone damage to increase or decrease? Atmospheric CO2 levels have risen by 30% and O3 concentrations are 2 to 3 times higher than pre-industrial levels. Percy et al (2002) evaluate the combined effects of increases (approximately doubling pre-industrial values) of ozone and carbon dioxide on aspen, which is the most prevalent North American tree species. Results show that enhanced growth due to increases in CO2 seem to offset the negative effects of O3. The impact of the combined effects of CO2 and O3 on pests is more complicated, since the pest, its source of sustenance (condition of the leaves on which it survives), and viability of its predators all must be considered. Fungal infestations (leaf rust) increased due to damaging effects of O3 that are not offset by increases in CO2. Tent caterpillars populations tended to increase under elevated O3, and the combined effects of aphids and their natural enemies were more negative to tree growth under the combination of enhanced CO2 and O3. The authors conclude that declines in forest health and forest ability to sequester additional atmospheric CO2 due to the combined effects of elevated CO2 and O3 must be considered in evaluating future productivity of northern forests.
Reference
Percy, K. E., C. S. Awmack, R. L. Lindroth, M. E. Kubiske, B. J. Kopper, J. G. Isebrands, K. S. Pregitzer, G . R. Hendrey, R. E. Dickson, D. R. Zak, E. Oksanen, J. Sober, R. Harrington, and D F. Karnosky, 2002: Altered performance of forest pests under atmospheres enriched by CO2 an O3. Nature, 420, 403-407.