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The assumption that the roughness Reynolds number (Re∗) can be used as a basis for quantifying the boundary-layer property kB-1(=ln(z0/z0T)) as in some modern numerical models is questioned. While Re∗ is a useful property in studies of pipe flow, it appears to have only marginal applicability in the case of treeless terrain, as studied in the two experimental situations presented here. For both the daytime and night-time cases there appears to be little correlation between kB-1 and Re∗. For daytime, the present studies indicate that the assumption kB-1≈2 is acceptable, while for night-time, the scatter involved in relating kB-1 to Re∗ suggests there is little reason to assume a direct relationship. However, while the scatter affecting all of the night-time results is large, there remains a significant correlation between the heat and momentum fluxes upon which an alternative methodology for describing bulk air-surface exchange at night could be constructed. The friction coefficient (Cf) and the turbulent Stanton number (St∗) are discussed as possible alternatives for describing bulk properties of the air layer adjacent to the surface. While describing the surface roughness in terms of the friction coefficient provides an attractive simplification relative to the conventional methodologies based on roughness length and stability considerations, use of the Stanton number shares many of uncertainties that affect kB-1. The transitions at dawn and dusk remain demanding situations to address. [ABSTRACT FROM AUTHOR]