A RADIATIVE-TRANSFER MODEL APPLIED TO A Y OUNG BEECH PLANTATION

A radiative transfer model developed for row crops (Sinoquet, INRA-Cle rmont-Ferrand, France) was applied to a young beech row plantation, pa rtly sheltered by a mature forest. The leaf area index of the forest w as estimated by a LAI 2000 PCA (plant canopy analyser), and the leaf a rea uniformly distributed within the canopy. In each row, 15 beech tre es were measured to establish the main dimensions of the mean tree and its crown. The rows were then modelled as a series of mean individual plants, whose leaf area was estimated from an allometric relationship with the diameter of the trees, and then uniformly distributed within the crowns. The test of the model was based on radiation measurements in the PAR waveband below and above the rows. With regard to transmit ted radiation above the five rows, the outputs of the model were in cl ose agreement with the measurements. In spite of large discrepancies i n the estimation of transmitted radiation at ground level, global resu lts suggest that the model correctly approximates light distribution i nside the plantation. By testing a few simple hypotheses, it was shown that the fine structure of young beech trees (spatial variation in le af area density, clumping) needs to be further investigated. This appr oach, suited to account for any canopy structure, appears to be a usef ul predictive tool for assessing the radiation environment within spec ific discontinuous canopies.