Abstract:Linear (Y=b×X) and nonlinear (y=b ×Xc) relations of leaf area (AL) With leaf length(L), leaf width(W), L2, W2 and LW were developed in Salix viminalis at the single leaf level, and used to assess leaf area at whole shoot level. Most relationships were significantly nonlinear, but both types exhibited good fits as indicated by r2 which was 0.941 (W)-0.998(LW) for the linear, and 0.982(W,W2)-0.998(LW) for the nonlinear equations.The nonlinear relationship between AL and LW was different for leaves from proleptic and sylleptic shoots, and varied with the growth stage. The nonlinear regression of AL on leaf dry weight (WL) varied with the leaf type and vertical position on shoot. Differences in leaf shape could be modelled successfully by geometric shapes, and leaf area could be obtained adequately with the hasal part of the leaf as a parabola and the distal part as an ellipse. The nonlinear equation performed better than the linear when used to predict the leaf area of the proleptic shoot (AP) with its diameter (D), length (H), D2H, D times the number of leaves (NL·D) on it alone, and the inaccuracy of the estimates of AP by both equation types could be increased after the emergence of the sylleptic shoots. With the nonlinear equation,leaf area of the sylleptic shoot (AS) could be predicted by its number within the proleptic shoot times D (NSS·D) or by its dry weight (WS) alone. All the nonlinear relationships of AP, As on shoot characters for both shoot types varied with the sampling occasion.