Regional Ozone Pollution Research Articles

Interactive effects of ambient ozone and climate measured on growth of mature forest trees

GLOBAL increases in concentrations of tropospheric ozone are of worldwide concern because of its potential to affect both human and ecological health1. Ozone has been implicated in the declining health of some forest tree species2,3 because of its effects on many growth-related processes in controlled studies3–5. Despite strong evidence that growth of forest tree seedlings can be reduced by ambient levels of ozone6, there has been little basis for evaluating the threshold and magnitude of direct effects on growth of mature, economically important forest trees. We describe here a five-year study of serial changes in stem circumference of 28 mature loblolly pine (Pinus taeda L.) trees. This study has defined a rough ozone response threshold and quantified short- and longer-term components of growth responses to varying ozone and climate variables. Ozone exposures at ≩40 nl 1−1 interacted with low soil moisture and high air temperatures to reduce short-term rates of stem expansion. Annual growth was also inversely related to seasonal ozone exposure and soil moisture stress. Effects varied widely between individual trees and years. Future ozone effects on forests are likely to be influenced by climate change and by projected increases in regional ozone pollution in industrialized countries.