Analysis of crown efficiency in a Common Beech thinning trial using a process-based model.

In order to design a simulator of local, intensive silviculture to the bene fit of future crop trees in Common Beech, an individual-tree growth model w as built using ecophysiological assumptions. This linear model links stem g rowth and crown size. The proportionality factor is named crown efficiency. This macroscopic parameter may be obtained as a combination of several ele mentary ecophysiological parameters (photosynthetic efficiency, allocation coefficient to stem, respiration coefficients etc.). The simple structure o f the model allows the analysis of crown efficiency variations in a thinnin g trial. We show that: thinning directly increase crown efficiency; canopy closure and climatic fluctuations lead to large differences of crown efficiency between successive periods; in order to show an effect of age, the mathematical structure of the model should be improved, e.g. by a better account of maintenance respiration and geometry of the annual ring.