An assessment of the impact of FIA's default assumptions on the estimates of coarse woody debris volume and biomass

Abstract

Currently, Forest Inventory and Analysis estimation procedures use Smalian's formula to compute coarse woody debris (CWD) volume and assume that logs lie horizontally on the ground. In this paper, the impact of those assumptions on volume and biomass estimates is assessed using 7 years of Oregon's Phase 2 data. Estimates of log volume computed using Smalian's formula are known to be biased, overestimating volume. On the other hand, volumes estimated from the diameter at the point of intersection between the log and the transect are approximately unbiased, regardless of log shape, but may be more variable. In Oregon, Smalian's formula overestimated CWD volume and biomass by 3.6 and 4.2 percent, respectively, compared with the intersection diameter method, or 1.7 and 2.0 times the standard error of the estimates. The impact on the variance of the estimates was negligible. The assumption that logs lie horizontally would result in an underestimation of the total CWD volume. The sensitivity to this assumption was examined under several scenarios, suggesting that the bias may be between 4.1 and 8.1 percent of the volume estimates.

Parent Publication

• Forest Inventory and Analysis (FIA) Symposium 2008; October 21-23, 2008; Park City, UT

Citation

Monleon, Vicente J. 2009. An assessment of the impact of FIA's default assumptions on the estimates of coarse woody debris volume and biomass. In: McWilliams, Will; Moisen, Gretchen; Czaplewski, Ray, comps. Forest Inventory and Analysis (FIA) Symposium 2008; October 21-23, 2008; Park City, UT. Proc. RMRS-P-56CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 8 p.