Sample size and variability of fuel weight estimates in natural stands of lodgepole pine

Abstract

This study assessed the variability of sample estimates for downed and dead woody fuel weight in natural lodgepole pine (Pinuscontorta Dougl.) stands using line-intersect sampling procedures. Equilateral triangles (30 m/side) were established at each of 40 sample sites with variable length transects on each side to estimate fuel weights by diameter class. Regardless of the number of sides measured, the standard error for fuels less than 7.0 cm was at most 20% of the mean. Even measuring only one side of the triangle, using a single transect instead of the triangular sample unit, still achieved standard errors less than 20% of the mean. Standard errors for classes greater than 7.0 cm were all greater than 20% of the mean. For these classes, more samples are required to achieve the 20% standard error limit; however, depending on costs, the triangular sample unit may not be the best solution. In this study, intracluster correlations were above 0.7 for the fuel diameter classes greater than 7.0 cm, suggesting that multiple transects at a given sample location contribute little new information. This effect, although less pronounced, was also observed with the smaller diameter classes.

Design unbiased estimation in line intersect sampling using segmented transects

“…For fixed L, multiply segmented transects make for a more local search around the sample point relative to straight line transects. As such, estimates of s from segmented transects are likely to be more variable when particles exhibit a clumped spatial structure, as discussed by Marshall et al (2000; see also Delisle et al, 1988). One reviewer of this manuscript maintained that segmented transect designs were very efficient for sampling populations composed of linear particles.…”

“…Examples include the Vegetation Resources Inventory of British Columbia, Canada, in which L-shaped transects are implemented; the Forest Inventory and Analysis program of the U.S. Forest Service and the National Forest Inventory of Switzerland, which utilize Y-shaped transects; the Canadian National Forest Inventory, which prescribes +-shaped transects; and the National Inventory of Landscapes in Sweden program, which has established square transects. In related applications, triangular transects have found use in assessments of forest fuels (Delisle et al, 1988).…”

Wildland Fuel Fundamentals and Applications

“…Several studies have compared traditional sampling techniques and PDS methods and variants to evaluate their performance, accuracy, and bias in measuring CWD (Bate et al 2004;Delisle et al 1988;Lutes 1999;Jordan et al 2004;Woldendorp et al 2004). Gove et al (2013) compared PDS variants using simulation modeling and found unbiased estimators of CWD using all variants and the differences in variances were small across all variants so selection of the most appropriate variant depends on field conditions.…”

Preliminary study on the assessment of deadwood volume by the French national forest inventory

“…As the frequency of CWD generally increases with decreasing diameter size, some CWD methodologies determine the length of a transect (or length of a transect section) to be sampled by a diameter of woody debris, particularly when fine woody debris is included (Delisle et al, 1988;Woodall and Williams, 2005). In these methods, transects are divided into sections, and measurements on these sections correspond to diameter size classes.…”