Philip J. Radtke

Ground-based Laser Imaging for Assessing Three-dimensional Forest Canopy Structure

Improved understanding of the role of forests in carbon, nutrient, and water cycling can be facilitated with improved assessments of canopy structure, better linking leaf-level processes to canopy structure and forest growth. We examined the use of high-resolution, ground-based laser imaging for the spatially explicit assessment of forest canopies. Multiple range images were obtained and aligned during both leaf-off and leaf-on conditions on a 20 m × 40 m plot. The plot location was within a mixed species broadleaved deciduous forest in western North Carolina. Digital terrain and canopy height models were created for a 0.25 m square grid. Horizontal, vertical, and three-dimensional distributions of plant area index, created using gap-fraction based estimation, had 0.5 m resolution for a cubic lattice. Individual tree measurements, including tree positions and diameter at breast height, were made from the scanner data with positions, on average, within 0.43 m and diameters within 5 cm of independent measurements, respectively. Our methods and results confirm that applications of ground-based laser scanning provide high-resolution, spatially-explicit measures of plot-level forest canopy structure.

Conditioning a distance-dependent competition index to indicate the onset of inter-tree competition

Data from a loblolly pine (Pinus taeda L.) spacing trial were used to investigate relationships between a distance-dependent competition index (CI) and the inflection age of sigmoidal single-tree cumulative basal area curves. Inflection ages increased with increasing initial growing space (GS), consistent with the hypothesis of maximum usable GS. Competition intensity as measured by the CI was generally smallest at a given point in time for trees with large inflection ages, but the trend varied by planting density. CI values at the inflection age also varied with planting density. The CI was modified so that it gave a constant CI value at the inflection age, on average, across all planting densities. Effects of site quality were accounted for to a limited degree, but the range of sites was narrow in the spacing trial. The modified CI should be useful as an absolute measure of competition independent of spacing.