Biomass Data from Sector Subsampling of 360˚ Spherical Images

Spherical photos were obtained a 1.6m and 2.6m above the ground. Photo horizontal point sampling (Wang et al. 2020) using a 2 M photo basal angle gauge was used to estimate basal area at each sample point using the 1.6m spherical photo. Sector subsampling was then used to select measure trees using a randomly generated sector azimuth and a sector angle of 7.2˚ (2% of 360˚).

All visible trees within each sector were then measured for total height and diameter at breast height using the spherical stereographic techniques. Biomass was then estimated using the Canadian National Biomass Equations, assuming all sector-selected trees were balsam fir. The plot-level data and measure-tree data were used to estimate aboveground biomass (BM, tonnes∙ha-1) using simulated resampling of the photo sample point data and ratio estimation.