Leaf allometry of Salix viminalis during the first growing season.

We established linear and exponential relationships between leaf area (A) and leaf length (L), leaf width (W), W(2), L(2) and LW, in Salix viminalis L. Most relationships were significantly nonlinear, but good fits were obtained with both linear and exponential models. The nonlinear relationship between A and LW differed for leaves from sylleptic and proleptic shoots. Leaves from sylleptic and proleptic shoots also differed in specific leaf area (area/weight). Leaf shape (width/length ratio and position of maximum leaf width) changed with leaf size and differed for leaves from sylleptic and proleptic shoots. Leaf area could be modeled adequately using implicit shape descriptions. A good fit was obtained when the basal and distal parts of the leaf were described as a parabola and an ellipse, respectively. The average area of single leaves and specific leaf area increased both along vertical profiles within shoots and during the growing period. Our results (1) indicate that nonlinear models should be used to estimate leaf area from linear leaf dimensions for plant species with leaves that vary in shape with leaf size, and (2) demonstrate the dependence of leaf characteristics on both sampling date during the growing season and spatial position in the canopy.