Predicting forest stand characteristics with airborne scanning laser using a practical two-stage procedure and field data

Abstract

The mean tree height, dominant height, mean diameter, stem number, basal area, and timber volume of 144 georeferenced field sample plots were estimated from various canopy height and canopy density metrics derived by means of a small-footprint laser scanner over young and mature forest stands using regression analysis. The sample plots were distributed systematically throughout a 1000-ha study area, and the size of each plot was 200 m 2. On the average, the distance between transmitted laser pulses was 0.9 m on the ground. The plots were divided into three strata according to age class and site quality. The stratum-specific regressions explained 82–95%, 74–93%, 39–78%, 50–68%, 69–89%, and 80–93% of the variability in ground-truth mean height, dominant height, mean diameter, stem number, basal area, and volume, respectively. A proposed practical two-stage procedure for prediction of corresponding characteristics of entire forest stands was tested. Sixty-one stands within the study area, with an average size of 1.6 ha each, were divided into 200 m 2 regular grid cells. The six examined characteristics were predicted for each grid cell from the corresponding laser data utilizing the estimated regression equations. Average values for each stand was computed. Most stand level predictions were unbiased ( P>.05). Standard deviations of the differences between predicted and ground-truth values of mean height, dominant height, mean diameter, stem number, basal area, and volume were 0.61–1.17 m, 0.70–1.33 m, 1.37–1.61 cm, 16.9–22.2% (128–400 ha −1), 8.6–11.7% (2.33–2.54 m 2 ha −1), and 11.4–14.2% (18.3–31.9 m 3 ha −1), respectively.