Tree size distribution functions of four boreal forest types for biomass mapping

Abstract

To accurately map forest biomass, which is essential for many socioeconomic and environmental studies, reliable information of tree size distribution within a stand is needed. Using measurements at 87 stands of trembling aspen (Populous tremuloides Michx.), jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana [Mill.] BSP.), and mixed forests along a 1,000-km boreal forest transect in western Canada, we investigated three methods for estimating tree size distribution: parameter prediction method for diameter-frequency distribution (PPM-Nk/N), PPM for diameter-basal area distribution (PPM-Bk/B), and parameter recovery method for diameter-frequency distribution (PRM). For diameter-frequency distribution estimation, the PPM-NK/N and the PRM were more accurate than PPM-BK/B. For biomass estimation, the PPM-BK/B and the PRM were found to have mean estimation errors <3% and root mean square errors <10%, relative to the "true" values given by summation overall trees, but the PPM-N K/N didn't perform as well. Three distribution functions (i.e., the Weibull, the Johnson's SB, and the lognormal) were used for each method but were found to make little difference in method performance. An additional test indicated that the PPM-BK/B and the PRM performed equally well for a balsam fir (Abies balsamea [L.] Mill) stand in eastern Canada.