Canadian Forest Service Publications
Comparison of geospatial and ground-based methods for determining postharvest dispersed woody residues. 2019. Trofymow, J.A., Kelley, J., Gougeon, F. Can. J. For. Res. 49: 1277–1288.
Issued by: Pacific Forestry Centre
Catalog ID: 39901
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Postharvest woody residues are measured to estimate billable waste, bioenergy potential, fuel loadings, and carbon budgets. In fall 2014, a waste and residue survey (WRS) established twenty-nine 0.4 ha plots in the dispersed residue stratum on two cutblocks on Vancouver Island, British Columbia, and measured woody residue “logs” ≥ 10 cm inside-bark diameter and ≥ 20 cmin length. A line-intersect sampling (LIS), in spring 2015, measured all woody debris ≥ 10 cmdiameter outside bark (DOB) on 18 plots. High-resolution (2 cm) photography was acquired in summer 2015, orthophotomosaics were prepared and analyzed for residue “logs” ≥ 10 cm DOB in 29 plots using semi-automated “log” delineation (SLD) and manual heads-up “log” digitization (MLD). After adjustment for bark thickness, SLD values were still higher than WRS values, due to inclusion of non-log pieces, though MLD values were not. LIS values were not different from WRS values once adjusted for bark thickness, transect overlaps, and decayed or non-log pieces excluded. The LIS and preharvest forest cover species composition differed from the WRS. While the SLD geospatial method can census ≥ 10 cm diameter residues in entire cutblocks, it was biased. Field-based methods may be required to correct SLD bias and measure species composition to determine bark thickness and wood densities to calculate biomass from residue volumes.
Plain Language Summary
After forest harvest, remaining woody residues are measured to estimate bioenergy potential, billable waste and carbon budgets. On two cutblocks on east Vancouver Island, remote sensing methods using high resolution imagery from unmanned aerial vehicles (UAV) where used to estimate volume, length and piece density of dispersed woody residues and compared to values from plots measured by ground-based waste and residue survey (WRS) and a line intercept method (LIM). The improved semi-automated log delineation (SLD version 3.7) and manual log delineation (MLD) geospatial methods both gave higher values than the WRS, however were more comparable, but still slightly higher, to the WRS when adjusted for bark thickness. This was likely due to inclusion of non-log pieces and differences in how average log width was calculated. LIM values were not different than WRS values once adjustments were made for transect overlaps and bark, and decayed and non-log pieces excluded. LIM species volume percentages differed from the WRS method. While geospatial methods can census >10cm residues in an entire cutblock, a combination of geospatial and field-based methods will likely be required to determine biomass since this can need information on woody residue species, bark thickness, and grade.