Light Use Efficiency and Woody Biomass Production of Poplar and Willow

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Abstract
Stands of clonal Salix viminalis (in 1985) and Populus trichocarpa (in 1986) were grown for one growing season from cuttings in containers, at 0.3 m spacing, supplied with trickle irrigation and nutrients. Woody biomass production (B w ) in the first year was analysed as the product of the proportion of dry matter partitioned to wood (η¯), the seasonal mean efficiency with which intercepted light was used to produce dry matter (ɛ¯), the mean fraction of incident light intercepted by the canopies (f¯), and the amount of incoming solar radiation over the season (A). Thus, Bw = η¯f¯ɛ¯A. For Salix , B w =10 t ha −1 y −1 , while for Populus , B w = 5 t ha −1 y −1 , mainly because of differences in η¯ and f¯. The Populus partitioned more dry matter to roots (and correspondingly less to stems) and intercepted less light over the growing season. The Salix and Populus clones had surprisingly similar (ɛ¯) values, namely 1. 58 and 1. 50 g MJ −1 , respectively (based on total dry matter and total solar radiation), which are very like the ɛ¯ values measured on C 3 agricultural crops in Britain. Also, the Salix and Populus clones produced canopies with similar light extinction coefficients and hence similar relationships between fractional interception and leaf area index.