PARENT SESSION
Oral Session #4: Plant Ecology: Gas Exchange. Presiding: J. Pereira.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas P&Q.
Biophysical controls of carbon flows in three successional Douglas-fir stands based upon eddy-covariance measurements.
Chen, Jiquan1, Falk, Matthias2, Euskirchen, Eugenie1, Paw U, Kyaw Tha2, Suchanek, Tom2, Ustin, Susan2, Bond, Barb3, Brosofske, Kim4, 1 2 3 4
ABSTRACT- We used the eddy-covariance method to directly measure exchanges of CO2 and H2O at three successional Pseudotsuga menziesii forests in the Wind River valley of southern Washington between 6/15 and 10/15 of 1998 and 1999. The primary objective of this study was to explore and identify the key biophysical variables that drive carbon exchange between evergreen, coniferous forests and the atmosphere within a chronosequence of the dominant vegetation type in the Pacific Northwest. We used the Landsberg model, logarithmic power function, and regression to explore the potential influences of major biophysical variables on FCO2 and potential thresholds controlling FCO2. Overall, given the same light levels, FCO2 was significantly higher (P<0.0001) at the young stands than at the old-growth forest. The average summer and early autumn FCO,2values were 2.2, 3.2, 6.1 and 4.2 (
mol. m^-2^.s^-1^) for OG98, OG99, 40Y98, and 20Y99, respectively. VPD was inversely and significantly correlated with FCO2 at all three stands, but the slope of this relationship at the old-growth forest was steeper than at the young stands. Correlations between FCO2 and all other environmental variables varied among ecosystems, with soil temperature showing a negative correlation and net radiation showing a positive correlation. WUE of the old-growth forest was significantly greater in the dry summer of 1998 than in 1999, when soil moisture was greater (P<0.0001) with average WUE values of 2.67 and 1.02 mg.g^-^1 for OG98 and OG99, respectively.
KEY WORDS: carbon, eddy-covariance, Douglas-fir, WUE