Comparison of geospatial and ground-based methods for determining postharvest dispersed woody residues

Abstract

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 cm in length. A line-intersect sampling (LIS), in spring 2015, measured all woody debris ≥ 10 cm diameter 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.

Combining Area-Based and Individual Tree Metrics for Improving Merchantable and Non-Merchantable Wood Volume Estimates in Coastal Douglas-Fir Forests

“…The Northwest Bay (NWB) site is located west of Nanaimo, B.C. (Figure 1), and had two blocks that were harvested in 2014 [40]. Prior to harvest, both blocks were primarily second-growth Douglas-fir with lesser amounts of western hemlock and western redcedar (Table 1).…”

“…The average elevation at NWB 193423 (612 m) was the highest of any blocks and was more than 150 m higher than NWB 193401 (Table 1). Both NWB 193401 and 193423 were harvested over the summer and fall of 2014 [41].…”

“…All imagery contained three channels (red, green, and blue) and had various delivered spatial resolutions and positioning accuracies (Table 2). The imagery at the OR site [15] and NWB site [41] had been used in previous studies developing post-harvest geospatial survey methods, whereas imagery from the FR site was newly acquired for this study (Table 2).…”

“…Similarly, the traditional method to measure and estimate non-merchantable volumes in a harvest block uses sample estimates from plots or transects and then scaling up sample estimates to the stratum or block-level [40]. These methods are limited because they also depend on the number and location of sample plots, which underestimate total nonmerchantable volumes [15].…”

“…These methods are limited because they also depend on the number and location of sample plots, which underestimate total nonmerchantable volumes [15]. However, recent methods have been developed to conduct a complete census of non-merchantable volume in the harvest block using a semi-automated log delineation method (SLD) [41].…”