Another definition of forest canopy height

Forest canopy height, the height of the highest vegetation components above ground level, is essential in normalizing micrometeorological parameters and in estimating forest biomass and carbon pools, but previous definitions of forest canopy height from inventory data bear uncertainties owing to arbitrary criteria of tall trees accounting for top height (i.e. mean height of tall trees selected by a certain definition) or to the effect of many shorter understory trees on Lorey's mean height (i.e. mean height weighted by basal area). We proposed a new concept of forest canopy height: the representative height of taller trees composing the crown surface or the upper canopy layer estimated on the basis of cumulative basal area from the shortest tree plotted against corresponding individual tree height. Because tall trees have large basal area, the cumulative basal area showing a sigmoidal curve would have an inflection point at a height class where many tall trees occur. Hence the forest canopy height is defined as the inflection point of the sigmoid function fitted to the cumulative basal area curve. This new forest canopy height is independent of the presence or absence of many shorter understory trees unlike Lorey's mean height, and is free from the definition of selecting the trees composing the upper canopy to determine their mean height. Applying this concept to actual forests, we found the new canopy height was larger than the arithmetic mean height and Lorey's mean height, and it was close to the aerodynamic canopy height determined by micrometeorological method, not only in the birch forest (even-aged pure stand) but also in the complex mixed forest of evergreen conifer and deciduous broadleaf species. Therefore the new canopy height would be suitable for intersite comparison studies and ground truth for remote sensing such as airborne laser scanning (ALS).