© 1996 Heron Publishing—Victoria, Canada
Canopy development, CO2 exchange and carbon balance of a modeled agroforestry tree
Pekka Nygren (1, 2), Pasi Kiema (1) and Silvia Rebottaro (3)
1. Forestry Field Station, University of Helsinki, FIN-35500 Korkeakoski, Finland / 2. INRA des Antilles-Guyane, Unité Agropédoclimatique, B.P. 515, F-97165 Pointe-à-Pitre, France / 3. Universidad de Buenos Aires, Facultad de Agronomía, Catedra de Dasonomía, Avenida San Martín 4453, (1417) Buenos Aires, Argentina / Received August 18, 1994
Summary
We developed a whole-canopy CO2 exchange simulation model to study effects of pruning on the carbon balance of trees. Model inputs include global short-wave
radiation, photosynthetic photon flux density (PFD), air temperature, time series of the development of canopy diameter, height
and total leaf area during the simulation period and local geographical and atmospheric parameters. Canopy structure is derived
stochastically from the time series of canopy development and growth functions of individual phytoelements. The PFD incident
on a phytoelement is computed from the average gap frequency of the canopy and the binary random probability of sunflecks
on the phytoelement. Instantaneous CO2 assimilation rate of each phytoelement is computed from PFD and phytoelement age. Assimilation rates are integrated over
space and time to estimate whole-canopy CO2 assimilation. The model was used to study carbon balance in five sources of the leguminous agroforestry tree Erythrina poeppigiana (Walpers) O.F. Cook during two 6-month pruning intervals. The canopy description appeared to be realistic. According to the
simulations, cumulative assimilation did not provide enough carbon for tree growth until two months after pruning, indicating
dependence of tree growth on reserve carbohydrates. The two most productive sources, which had the most open canopies, were
the most dependent on reserve carbohydrates after pruning.
Keywords:
allocation, biomass production, canopy photosynthesis, Erythrina poeppigiana, pruning, radiation regime, simulation.
