Measuring heights to crown base and crown median with LiDAR in a mature,even-aged loblolly pine stand

This study evaluated the possibility of measuring the height to the base of the live crown and the height to the median of canopy elements with airborne scanning LiDAR (Light Detection And Ranging) in a simple, even-aged stand of loblolly pine. The first step in determining these heights was fitting truncated Weibull functions to the vertical distribution of elevations where discrete laser pulses were reflected from the dominant canopy strata. The height to the canopy median was defined as height at the median of the distribution. The height to the base of the live crown was defined as the height where the upper tail the distribution asymptotes to zero returns. Ground-based and LiDAR-based estimates of the canopy median differed by 0.3 m and were not significantly different (P = 0.23). Ground- and LiDAR-based estimates of the base of the live crown differed by 0.6 m and were significantly different (P = 0.03). LiDAR-based estimates of the canopy median exhibited positive bias over most of the range of field-measured values. Analyses of the LiDAR data resulted in overestimating the height to the canopy base over most of the range in field-measured values; however, the difference between ground and LiDAR-based estimates were negatively correlated with ground-based measurements. Average tree diameter was calculated with LiDAR-generated heights to the canopy median and to the base of the live crown. The overall average diameter was not statistically different from the overall quadratic mean diameter measured on the ground, demonstrating the possible utility of these canopy variables to forest managers working with simple stands such as plantations.