Aerodynamic scaling for estimating the mean height of dense canopies

摘要

We used an aerodynamic method to objectively determine the representative canopy height, using standard meteorological measurements. The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused on creating a standard for determining the representative canopy height. Here we propose the ‘aerodynamic canopy height’ ha as the most effective means of resolving the representative canopy height for all forests. We determined ha by simple linear regression between zero-plane displacement d and roughness length z0, without the need for stand inventory data. The applicability of ha was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory data showed that ha was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure, or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The linear relationship between d and z0 was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the canopy were continuous and smooth at canopy height. This was supported by observations, which showed that ha was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability of ha was also verified using data from several previous studies.