Heat, mass and momentum transfer, and the turbulence regime within a plant canopy, are dependent upon aerodynamic variables which are non-linearly related to wind speed. Measurements made in plant canopies show that turbulence is intermittent and non-Gaussian. Therefore, a statistical question arises when evaluating non-linear wind speed-dependent, aerodynamic variables: is the mean value of an aerodynamic function equal to that function evaluated at the mean wind speed? We evaluated the above-stated, statistical question for boundary layer resistances to mass and momentum transfer, the form drag force and the rate of work against form drag. Pertinent computations were based upon turbulence measurements made within a fully leafed, deciduous forest. In addition, expected values of these aerodynamic variables were computed with probability density functions derived from the Gram-Charlier expansion series. Boundary layer resistances for water vapor ( R b) and momentum ( R m), computed with mean wind speeds, underestimate mean functional values by 5–20%. On the other hand, estimates of R b and R m derived from probability density functions underestimate mean functional values by < 3%. Computations of the form drag force, based on probability density functions and mean wind speeds, respectively, overestimate and underestimate mean functional values by ∼ 20%. Theoretically, the form drag force in the streamwise direction is a function of the product of the horizontal wind velocity and the scalar wind speed. Hence, parameterizing its value based only on scalar wind speed squared is apt to be error prone. Estimates of the rate of work against form drag, based on the probability density functions, agree within 5% of mean functional values. The rate of work against form drag computed on the basis of the mean horizontal wind speed cubed underestimates mean functional values by 30–60%. This underestimate, however, is expected since it represents the rate of work done by the mean wind, which is a different quantity.