Surface flux measurements from two contrasting sites within the FIFE study area are analyzed. The seasonal variation of midday latent heat fluxes and surface conductances at the two sites was found to be very similar even though the ratio of their average total leaf area indices was greater than two to one. Concurrent measurements made at another six flat sites within the FIFE area confirmed the independence of latent heat flux with respect to leaf area index. The surface conductance stress function related to specific humidity deficit was the same for the two sites, whereas the solar radiation stress function showed a difference of 30% at a solar radiation input of 300 W m−2 and the soil moisture stress function showed a difference of 16% when half the extractable soil moisture had been taken up. However, when the stress functions were combined to determine the surface conductance, these differences virtually canceled out.