A pseudo-3D model to optimise the target traits of light interception in short-rotation coppice willow

Fast growing short rotation coppice willows are being developed as biomass crops for bioenergy and biofuels. The UK Perennial Bioenergy Crops programme (BSBEC-BioMASS) aims to optimise biomass yield and wood composition of willow. Towards this goal, new trials were established in 2009 of contrasting genotypes (Endurance, Resolution, Terra Nova and Tora) in two different environments (wet and dry) for intensive studies and to increase our process understanding. From data of the first growth cycle we developed a model for light interception, representing the canopy structure, and accounting for both the vertical and horizontal heterogeneity of willow canopies. The key components of light interception were considered as: leaf inclination distribution and its effects on the extinction coefficient; clumping index; and leaf area index as a function of canopy height. The model realistically represents the varietal differences observed in the field and predicts well light interception for willow (r2 ranges from 0.91 to 0.99) when compared with measured data. The extinction coefficient proved to be well represented using a standard ellipsoidal distribution function (r2 ranges from 0.81 to 0.97). Vertical leaf area distribution and clumping index were found to be the most important traits for light interception and, unlike the extinction coefficient, the clumping index can be expressed as a function of the leaf area. We conclude that the new model provides a useful and simple approach to characterise the efficiency of light interception in willow genotypes and can help to identify target traits for the selection of varieties with an improved architecture for light interception.

► The dependence of the extinction coefficient on the canopy height is analysed.
► A pseudo-3D architectural model for light interception in Salix spp. is proposed.
► The clumping index is found to be extremely important trait for light interception.
► The model properly accounts for vertical leaf area heterogeneity in willow species.