Estimating tree heights and number of stems in young forest using airborne laser scanner data

The mean heights of dominant trees and the stem numbers of 39 plots of 200 sq m each were derived from various canopy height metrics and canopy density measured by means of a small-footprint airborne laser scanner over young forest stands with tree heights < 6 m. On the average, the laser transmitted 12,019 pulses/ha. Ground-truth values were regressed against laser-derived canopy height metrics and density. The regressions explained 83 and 42 percent of the variability in ground-truth mean height and stem number, respectively. Cross-validation of the regressions revealed standard deviations of the differences between predicted and ground-truth values of mean height and stem number of 0.57 m (15 percent) and 1209/ha (28.8 percent), respectively. A proposed practical two-stage procedure for prediction of mean height of dominant trees in forest stands was tested. One hundred and seventy-four sample plots were distributed systematically throughout a 1000-ha forest area. Twenty-nine of the plots were sited in young stands with tree heights < 11.5 m. In the first stage, mean height of dominant trees of the 29 plots were regressed against laser-derived canopy height metrics and density. In the second stage, the selected regression was used to predict mean height of 12 selected test stands. The prediction revealed a bias of 0.23 m (3.5 percent) (P > 0.05) and a standard deviation of the differences between predicted and ground-truth mean height of 0.56 m (8.4 percent). (Author)