Botanical determinants of foliage clumping and light interception in two-year-old coppice poplar canopies: assessment from 3-D plant mock-ups

Botanical parameters (e.g., shoot and branch inclination, petiole length, leaf phyllotaxy, size and shape) that influence light interception and foliage clumping in dense two-year-old monoclonal poplar (Populus spp.) coppice crops were analysed with a three- dimensional simulation model. Crop LAI varied from 1 to 2 for clone Ghoy and from 2.5 to 7.4 for clone Trichobel from May to September. Canopies were strongly clumped, with a clumping index (mu) about 0.5. Canopy light transmittance (tau) varied from 0.59 in May to 0.41 in September for clone Ghoy and from 0.42 to 0.08 for clone Trichobel, and was strongly associated with LAI. The overall e. ect of a simulated shift in botanical parameters was relatively small and resulted in limited changes in mu and tau by +/- 0.05 and +/- 0.1, respectively. Petiole length had the most notable effect on mu and tau, while the other parameters were less effective. However, biomass cost analyses showed that actual petiole length optimised the efficiency of biomass investment into light capture.