Simulation Studies on Line Intersect Sampling of Forest Residue

Author： Pickford Stewart G. Hazard John W.

Publisher： Society of American Foresters

ISSN： 0015-749X

Source： Forest Science, Vol.24, Iss.4, 1978-12, pp. : 469-483

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Abstract

Computer-simulated populations of logging residue were sampled by simulating the line intersect technique. Populations ranged from randomly distributed uniform cylinders containing 3,500 cubic feet per acre (244.90 m³/ha) to tapered pieces (frustums) containing 2,340 cubic feet per acre (163.73 m³/ha) whose diameter and length distributions resemble those found on Pacific Northwest clearcuts. Repeated sampling of these populations with fixed numbers and lengths of samples was conducted. Successive simulations differed in the number and lengths of lines employed. Results showed that (1) the line intersect method requires approximately 4,000 feet (1219.20 m) of line to achieve confidence intervals narrower than ±25 percent at the 95-percent probability in a random population of frustums with varying diameters and lengths; (2) populations of tapered pieces require substantially more sampling effort for a specified accuracy than a uniform population of cylinders, but piece taper introduces no additional bias in the estimated volume; (3) sample size necessary for a specified precision is inversely proportional to the piece density of uniform cylinders and increases substantially for populations containing pieces of varying diameters and lengths; (4) for a fixed total length of sample line, population variance estimated from repeated trials decreases with increasing length of individual sample lines; (5) estimated population variance decreases with increases in total sample length; (6) the product of line length and number of lines (total sample length) is the important criteria for controlling precision in random populations. Forest Sci. 24:469-483.