HR: 08:45h
AN: B41A-04 INVITED     [PDF]
TI: Are Isotope Models of Tree Ring Cellulose Useful for Studies on Ecosystem and Climate Change?
AU: * Roden, J S
EM: rodenj@sou.edu
AF: Southern Oregon University, Biology Department 1250 Siskiyou Blvd., Ashland, OR 97520 United States
AB: For many years, the carbon, oxygen and hydrogen stable isotopes of tree ring cellulose have been used to infer environmental change at ecosystem and global scales. Most climate change studies have been based on empirical correlations with measured or inferred meteorological information. Recently, mechanistic models have been developed to interpret and predict the isotopic composition of cellulose. These models help clarify what environmental information might be contained in historic cellulose records. Although it is best to test and parameterize these models under controlled environmental conditions, field-testing is also critical since the tremendous variability of environmental factors in natural habitats could obscure important signals. However, field-testing these models can be problematic due to the large number of parameters that need to be estimated. Two studies will be presented that test a model that predicts the stable oxygen isotope content of cellulose under field conditions. The model adequately accounted for field observations of riparian zone trees at three sites in Arizona, Oregon and Utah that had contrasting isotopic and environmental inputs. Although the cellulose model underestimated the oxygen isotopic content of tree ring cellulose in a study along a transect of decreasing water status in Oregon, it did predict the greatly reduced range in oxygen isotope content over the transect. Both studies show that ambient humidity plays an important role in modifying the primary signal of meteoric water isotopic content in organic matter. Thus, tree ring records could provide important proxy information regarding changes in ecosystem humidity. However, teasing out humidity information may not be trivial due to the number of other factors involved. The use of dual isotope records (carbon and oxygen) allow for better interpretation of environmental information since each isotope provides different, though related, information regarding ecosystem water status. In conclusion, although cellulose models are extremely useful for understanding what signals are potentially present in proxy data, correlating climate data with isotopic data may still be important in order to make inferences regarding ecosystem or global change from ancient tree ring records.
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 1851 Plant ecology
DE: 3344 Paleoclimatology
DE: 4221 Dendrochronology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting