Using airborne laser altimetry to assess and monitor biodiversity
Deanna Weller, Christian Witte, Celia Mackie, Dave Smith & Robert Denham
Queensland Department of Natural Resources, Environment Australia, CRC for Carbon Accounting, February 2001
About the publication
To demonstrate the potential of laser altimetry as a biodiversity assessment and monitoring tool, multiple passes have been conducted over three study sites at regular intervals over a two year period. The study sites were chosen to represent a range of forest conditions and stages; the first, a control site was established to monitor a mature forest maintained free from external disturbances such as logging, the second site acted as a treatment with standard selective timber harvesting monitored before and after logging, and the third, a new plantation site, provided the opportunity to monitor regrowth. Twenty-two sites in south-western Queensland were also chosen for a single helicopter pass, allowing for the demonstration of laser altimetry as an assessment tool over a variety of landscapes and forest types.
Laser data was captured at flying heights of 30 metres, 60 metres and 100 metres above the upper canopy level at each of the two year monitoring sites, to determine the effect of laser 'footprint' size on resulting foliage projected coverage (FPC) and tree height measurements. Field measurements of FPC and tree height were recorded at the same time as the laser data capture and were found to be highly correlated with laser data estimates (correlation coefficients of 0.92, 0.94, and 0.96 were obtained for FPC analysis and 0.91, 0.93, and 0.91 for tree height analysis).
The monitoring of changes in FPC and tree height with time was also highly successful. For example, a drop in FPC was clearly observed after the logging event at the harvest site, and was followed by a gradual increase in FPC with time as regrowth occurred. The growth increase at the plantation site was also clearly observed through both FPC and tree height data.
The interpretation of high-resolution digital video, captured at the same time as the laser data, provided information on forest type, species type and growth stage of trees. The number of dominant species matches obtained through a comparison of field and video data was 15 out of a possible 22 western sites, and it is expected that this result would further improve with a small degree of field calibration by the video interpreter.