Second-order turbulence moments of vertical velocity w, temperature &thgr;, and specific humidity q observed with an aircraft in the atmospheric surface layer over a flat maritime pine forest were used to investigate the applicability of the variance methods to variable terrain. The variances of w and &thgr; were found approximately to obey Monin-Obukhov similarity, while that of q clearly did not. Further investigation suggested the possibility that the surface variability affected the fluctuations of q and that it also caused a breakdown of the similarity between the scalars &thgr; and q. Different versions of the variance method were tested, and several of them were found to predict the surface flux of sensible heat with satisfactory accuracy. The latent heat flux estimates were in reasonable agreement when the dimensionless functions were calibrated locally. ¿ 1999 American Geophysical Union