Application of the bulk similarity formulation to the atmospheric boundary layer (ABL) requires the adoption of an external wind velocity and temperature scale. Recent versions of this approach have made use of the average wind speed and average temperature over the outer region or mixed layer of the ABL. The method is applied herein with wind profile data measured over the Landes forest in southwestern France to estimate the regional surface shear stress under unstable conditions. It is found that these estimates can be as reliable as those obtainable with Monin-Obukhov similarity of the atmospheric surface layer. ¿ American Geophysical Union 1996