Measuring ozone effects on ecophysiological processes of mature eastern deciduous forests.
McLaughlin, Samuel*,1, Wullschleger, Stan2, Nosal, Milo3, Sun, Ge4, 1 Dept. Ecology and Evolutionary Biology, Knoxville, TN, USA2 Evironmental Sciences Division, Oak Ridge, TN, USA3 Department of Mathematics and Statistics, Calgary, Alberta, Canada4 Southern Global Climate Change Program, Raleigh, NC, USA
ABSTRACT- High resolution measurements of stem growth and water use by mature forest trees in response to ambient ozone exposures indicate that tree growth rates were typically reduced 30-70% and rates of water use were increased in East Tennessee during 2002,a high ozone year. A generalized additive model of stem growth over the 2002 growing season identified ozone as a statistically and quantitatively significant negative influence on stem growth. Increases in sap flow, increases in estimated canopy conductance, and decreases in soil moisture near subject trees indicated that ambient ozone levels were significantly influencing forest water use and intensifying the adverse effects of a mild drought on tree growth and soil mositure status. In these analyses the patterns of episodically high ozone levels within an exposure year appeared to have more influence on observed responses than seasonally averaged levels over various thresholds. Analyses of streamflow data for three nearby forested watersheds for periods of up to 25 years indicated that late season stream flow was significantly reduced in higher ozone years. Empirically derived models of stem growth, sap flow, canopy conductance,soil moisture content, and late season streamflow all identified episodically higher ozone exposures as significant contributors to observed responses. Data indicate that ozone is an important component of current climate and that ozone will likely exacerbate the adverse effects of global warming on forest and stream ecosystems.
Key words: ozone, growth, water use, streamflow
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