Citation. Aber, J. D.; Reich, P. B.; Goulden, M. L. 1996. Extrapolating leaf CO₂ exchange to the canopy: a generalized model of forest photosynthesis compared with measurements by eddy correlation. Oecologia 106:257-265.

Abstract. Over the last four years, two data sets have emerged which allow increased accuracy and resolution in the definition and validation of a photosynthesis model for whole forest canopies. The first is a greatly expanded set of data on the nitrogen-photosynthesis relationship for temperate and tropical woody species. The second is a unique set of long-term (4 year) daily carbon balance measurements at the Harvard Forest, Petersham, Massachusetts, collected by the eddy-correlation technique. A model (PnED-Day) is presented which is derived directly from, and validated against, these data sets. The PnED-Day model uses foliar nitrogen concentration to calculate maximum instantaneous rates of gross and net photosynthesis which are then reduced for suboptimal temperature, photosynthetically active radiation (PAR), and vapor pressure deficit (VPD). Predicted daily gross photosynthesis is closely related to gross carbon exchange at the Harvard Forest as determined by eddy-correlation measurements. Predictions made by the full canopy model were significantly better than those produced by a multiple linear regression model. Sensitivity analyses for this model for a deciduous broad-leaved forest showed results to be much more sensitive to parameters related to maximum leaf-level photosynthetic rate (A_max) than to those related to light, temperature, VPD or total foliar mass. Aggregation analysis suggest that using monthly mean climatic data to drive the canopy model will give results to similar to those achieved by averaging daily eddy correlation measurements of gross carbon exchange (GCE).

Keywords. whole forest canopy, photosynthesis, foliar nitrogen concentration, model, gross carbon exchange