© 2006 Heron Publishing—Victoria, Canada
A comparative analysis of simulated and observed photosynthetic CO2 uptake in two coniferous forest canopies
Andreas Ibrom (1, 2, 3), Paul G. Jarvis (4), Robert Clement (4), Kai Morgenstern (5), Alexander Oltchev (1), Belinda E. Medlyn (6), Ying Ping Wang (7), Lisa Wingate (4), John B. Moncrieff (4) and Gode Gravenhorst (1)
1. Institute of Bioclimatology, Georg-August-University, D-37077 Göttingen, Germany / 2. Corresponding author (andreas.ibrom@risoe.dk) / 3. Bio Systems Department, Risø National Laboratory, DK-Roskilde, Denmark / 4. Institute of Atmospheric and Environmental Science, School of GeoSciences, The University of Edinburgh, Edinburgh, EH9 3JN,
Scotland, U.K. / 5. Biometeorology and Soil Physics Group, University of British Columbia, Vancouver, V6T 1Z4, Canada / 6. School of Biological, Earth and Environmental Sciences, The University of New South Wales, Sydney 2052, Australia / 7. CSIRO, Atmospheric Research, Private Bag # 1, Aspendale, Victoria 3195, Australia / Received August 6, 2004; accepted May 8, 2005; published online April 3, 2006
Summary
Gross canopy photosynthesis (Pg) can be simulated with canopy models or retrieved from turbulent carbon dioxide (CO2) flux measurements above the forest canopy. We compare the two estimates and illustrate our findings with two case studies.
We used the three-dimensional canopy model MAESTRA to simulate Pg of two spruce forests differing in age and structure. Model parameter acquisition and model sensitivity to selected model
parameters are described, and modeled results are compared with independent flux estimates.
Despite higher photon fluxes at the site, an older German Norway spruce (Picea abies L. (Karst.)) canopy took up 25% less CO2 from the atmosphere than a young Scottish Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation. The average magnitudes of Pg and the differences between the two canopies were satisfactorily represented by the model. The main reasons for the different
uptake rates were a slightly smaller quantum yield and lower absorptance of the Norway spruce stand because of a more clumped
canopy structure. The model did not represent the scatter in the turbulent CO2 flux densities, which was of the same order of magnitude as the non-photosynthetically-active-radiation-induced biophysical
variability in the simulated Pg. Analysis of residuals identified only small systematic differences between the modeled flux estimates and turbulent flux
measurements at high vapor pressure saturation deficits. The merits and limitations of comparative analysis for quality evaluation
of both methods are discussed. From this analysis, we recommend use of both parameter sets and model structure as a basis
for future applications and model development.
Keywords:
canopy photosynthesis model, carbon dioxide fluxes, eddy correlation, MAESTRA, Picea abies, Picea sitchensis.
