What is the best way to represent surface conductance for a range of vegetated sites?

Surface conductance G_s is a significant parameter for indicating the evaporative and photosynthetic properties of a vegetated surface. When comparing G_s values between different observation sites, some studies have used G_smax and others have used Ĝ_smax (where G_smax is the maximum G_s value measured during the measurement period, and Ĝ _smax is the maximum G_s value obtained with a vapour pressure deficit (VPD) of ≥1.0 kPa during the measurement period). In this study, we demonstrate a clear justification for using Ĝ_smax instead of Ĝ_smax when comparing G_s values between different sites. We examined whether both Ĝ_smax and G_smax lead to the same conclusions in classifying vegetated sites. Komatsu (2003b) [Hydrological Processes 17: 2503-2512] reported a clear relationship between canopy height h and Ĝ_smax for coniferous forests with a projected leaf area index (LAI) of ≥3.0. We examined not only the relationship between h and Ĝ_smax but also the relationship between h and G_smax for coniferous forests with a projected LAI of ≥3.0. Both Ĝ_smax and G_smax decreased with increasing h. However, the relationship between h and G_smax was less well defined than the relationship between h and Ĝ _smax because of biased G_smax data. Consequently, we conclude that Ĝ_sma'x is a more appropriate index than G_smax to represent G_s for sites with different vegetation.