Canopy model simplification, includes aspects such as modelling stomatal conductance, temperature dependence and upscaling in time. Scaling up from leaf to canopy imposes another important constraint to simplification.
A general canopy-scale photosynthesis model should be applicable to any forest anywhere on earth. In principle, such a model could be calibrated using canopy-scale flux measurements for a particular site, but to facilitate it's extrapolation to vegetations with different structure or composition, it is preferable to parameterize them to the scale of leaves and ecosystem components, since more information is available at that scale and leaf scale parameters are less dependent on the growing site. Subsequent scaling from leaf to canopy requires complex multi-layer models, since most physiological processes involved are non-linear and leaf parameters do vary with position in the canopy.
Several authors, however, have recently shown that such models can collapse to one set of
leaf-scale physiological relationships, linearly scaling up to the canopy, if photosynthetic capacities acclimate fully to the local light within the canopy. Although soil processes will still need to be taken into account separately, the consequences of
this assumption are extremely important for modelling of global carbon budgets. But the evidence for full acclimation is still scattered and not conclusive.
In this study, the assumption will be evaluated examining available data of light and photosynthetic capacities in forest canopies, including work carried out in BOREAS. Given full acclimation does not always occur, the sensitivity of big leaf models to the degree of (partial) acclimation to light will be assessed using a 3-dimensional canopy model (MAESTRO) as a reference.
Key words: canopy model, simplification, big leaf, photosynthesis, acclimation, PAR.
Correspondence: Bart Kruijt, University of Edinburgh, IERM, Darwin Building, Mayfield Road, Edinburgh EH9 3JU, UK
Telefax: +44-131-6620478
E-mail: b.kruijt@ed.ac.uk