A comparison between various definitions of forest stand height and aerodynamic canopy height

Abstract

A consistent measure of forest canopy height is required for among-site comparisons of meteorological properties and for comparison of model results such as distributions of wind and other scalars calculated by large eddy simulations with observations. The aerodynamic canopy height has been proposed as a useful measure of canopy height, which is determined by micrometeorological methods without depending on stand inventory data. However, the aerodynamic canopy height is obtainable only if the necessary meteorological instruments are installed. In this study, we explored an alternative measure of forest canopy height based on tree inventory data. When cumulative trunk basal area from the shortest tree is plotted against corresponding individual tree height, it shows a sigmoidal curve with its inflection point occurring at a height class. The above-ground height of this inflection point (hereafter cumulative basal area inflection (CuBI) height) is defined as forest canopy height, as many tall trees with relatively large basal area belong to this height class. The difference between the aerodynamic canopy height and the CuBI height was always smaller than 12%, whereas the differences exceeded 20% for at least one of the forests when canopy height was determined using alternate methods. This suggests that, unlike other canopy height definitions, CuBI height is a consistent index of the aerodynamic canopy height, little affected by criterion of the trees composing the upper canopy or by the presence/absence of many shorter understory trees. Because chronological changes in size-structure of tree height and trunk diameter have long been studied for many forests, CuBI height may be used as an index of chronological change in the aerodynamic canopy height.