Lidar remote sensing of biophysical properties of tolerant northern hardwood forests

Previous forest research using time-of-flight lidar data has primarily focused on forest ecosystems with conifers as the predominant tree type. In this study, small-footprint time-of-flight lidar data were used to estimate biophysical properties of tolerant hardwood forests composed predominantly of mature sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton) in the Turkey Lakes Watershed (TLW) near Sault Ste. Marie, Ontario. Ground reference data were collected during the first two weeks of July 2000 for 49 circular sample plots, each 0.04 ha (or 400 m2) in area. Lidar data were acquired on 24 August 2000 using an Optech ALTM 1225 (Optech Incorporated, Toronto, Ont.). Ten biophysical forest metrics were derived for each plot: (1) maximum tree height (hmax), (2) Lorey's mean tree height (hLorey), (3) mean diameter at breast height (DBH), (4) total basal area (BA), (5) percent canopy openness (CO%), (6) leaf area index (LAI), (7) ellipsoidal crown closure (CC), (8) total aboveground biomass (BIO), (9) total wood volume (VOL), and (10) stem density (SD). Likewise, three laser height metrics were derived for each plot: (1) maximum laser height (Lhmax), (2) mean laser height (Lhmean), and (3) mean laser height calculated from lidar returns filtered based on a threshold applied to the intensity return values (LhIR). The results demonstrate that for each forest with a given stand structure, there exists one or more laser height metrics derived from lidar data that are capable of providing an estimate of various biophysical properties. Lhmax was the best estimator of hmax (r2 = 0.79) and hLorey (r2 = 0.87); LhIR was the best estimator of BA (r2 = 0.85), BIO (r2 = 0.85), and VOL (r2 = 0.87); and Lhmean was the best estimator of CC (r2 = 0.89), DBH (r2 = 0.63), CO% (r2 = 0.76), LAI (r2 = 0.80), and SD (r2 = 0.86). The results illustrate the potential for laser height metrics to estimate (i) plot heights and stem densities, (ii) aboveground biomass and volume, and (iii) canopy-related measures.