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TREE-RING INDICES AND ISOTOPE SIGNATURES OF PINUS PONDEROSA RELATED TO HISTORIC OZONE CHANGES OUTSIDE LOS ANGELES
Gregg, J W., J R. Brooks, E H. Lee, AND N. E. Grulke. TREE-RING INDICES AND ISOTOPE SIGNATURES OF PINUS PONDEROSA RELATED TO HISTORIC OZONE CHANGES OUTSIDE LOS ANGELES. Presented at American Geophysical Union annual meeting, San Francisco, CA, December 8-12, 2003.
Ozone concentrations in the Los Angeles (LA) basin were at historic highs in the late 1970s. Since that time Clean Air regulations have helped lower ozone, but little is known of the long-term vegetation responses. Extensive research has used tree-ring indices together with the physiological and environmental information stored in the 13C and 18O signatures of tree-ring cellulose to understand past climates. Here, we used the forty-year ozone record from Camp Paivika, CA, the site in the San Bernardino mountains of the LA basin with both the longest record and the highest values, to determine climate versus ozone impacts on basal area increment and 13C and 18O signatures for Ponderosa Pine. Annual growth increment was significantly related to ozone and temperature but not precipitation. 13C showed the typical climatic pattern of becoming more enriched in warm dry years, but was more strongly related to ozone independent of climate effects. 18O was also enriched in warm, dry years, but was most strongly related to annual growth increment and showed no relationship with ozone. The relationship between 18O and growth is likely due to alterations in evaporative enrichment within the foliar tissues. Our results will be discussed in light of physiological processes and environmental variation responsible for alterations in 13C and 18O signatures.