Measuring forest structure and biomass in New England forest stands using Echidna ground-based lidar

A ground-based, upward-scanning, near-infrared lidar, the Echidna® validation instrument (EVI), built by CSIRO Australia, retrieves forest stand structural parameters, including mean diameter at breast height (DBH), stem count density (stems/area), basal area, and above-ground woody biomass with very good accuracy in six New England hardwood and conifer forest stands. Comparing forest structural parameters retrieved using EVI data with extensive ground measurements, we found excellent agreement at the site level using five EVI scans (plots) per site (R2 = 0.94–0.99); very good agreement at the plot level for stem count density and biomass (R2 = 0.90–0.85); and good agreement at the plot level for mean DBH and basal area (R2 = 0.48–0.66). The observed variance at site and plot levels suggest that a sample area of at least 1 ha (104 m2) is required to estimate these parameters accurately at the stand level using either lidar-based or conventional methods. The algorithms and procedures used to retrieve these structural parameters are dependent on the unique ability of the Echidna® lidar to digitize the full waveform of the scattered lidar pulse as it returns to the instrument, which allows consistent separation of scattering by trunks and large branches from scattering by leaves. This successful application of ground-based lidar technology opens the door to rapid and accurate measurement of biomass and timber volume in areal sampling scenarios and as a calibration and validation tool for mapping biomass using airborne or spaceborne remotely sensed data.

Research Highlights
► Ground-based, full-waveform, scanning Echidna lidar retrieves mean tree diameter, stem density, basal area, and above-ground biomass with R2=0.94-0.99.
► We scanned six 1-ha sites, five scans per site, in three New England forests including deciduous and coniferous stands.
► Best agreement is obtained when five scans are averaged to represent one hectare.
► Occlusion of far trunks hidden behind near trunks is corrected using geometrical probability theory.
► Biomass is estimated by a pooled allometric equation using the two leading dominant species at the site.