Carbon balance and tree growth in a Fagus sylvatica stand

The objectives of this study were 1) to scale photosynthesis 2) om leaf to crown and to tree scale, 2) to determine the proportion of assimilated carb on used for wood construction and whether the fi action of assimilation use d for production varies among social classes and 3) to validate the approac h by comparing assimilation estimates with independent measurements provide d by the eddy covariance technique (EC). Measurements (growth and gas excha nge) were performed in a 30-year-old Fagus sylvatica stand during the 1997 growing season on five sample trees of different crown classes (dominant, c odominant and intermediate trees). A nonlinear relationship between net CO2 assimilation and photosynthetically active radiation (PAR) was found for e ach sample trees. Canopy net CO2 assimilation was then modelled over a peri od of non limiting soil water soil water content. Simulated gross assimilat ion scaled to stand level was in good agreement with stand measurements per formed by EC.