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Two-Stage Forest Sampling: A Comparison of Three Procedures to Estimate Aggregate Volume

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Three two-stage forest sampling procedures are examined in order (1) to quantify the variance penalty (if any) associated with second-stage sample restrictions; and (2) to quantify the variance gains (if any) associated with the incorporation of tree height data at the second stage. The three two-stage procedures share a common first stage, i.e., horizontal point sampling (HPS), which selects trees with probability proportional to tree basal area. The second stage selection approaches vary, as follows: 1. Trees are selected with replacement with probability proportional to tree height from a single list composed of all trees sampled across all first-stage sample points. 2. Trees are selected with replacement with probability proportional to tree height from separate lists compiled on each first-stage sample point. 3. Trees are selected randomly, with replacement, on each first-stage point. The results indicate that little or no reduction in variance accrues from incorporating height data into the two-stage sample design for the three mapped stands considered. HPS/simple random sampling yielded variances ranging from 7.1% larger to 9.2% smaller than the smallest HPS/list sampling variance, while maintaining an advantage in an even-aged stand. It is hypothesized that the HPS/list sampling procedures may prove more useful in mature, all-aged stands where height may account for a significant portion of volume or biomass variation. No loss of precision is noted when second-stage sampling is restricted by point on these three forest tracts. An investigation into the effects of first-and second-stage sample sizes provide a convincing argument to select only one tree per first-stage sample point when sampling is restricted by point. Considering both precision of estimation and field efficiency, these results suggest that the HPS/simple random sampling procedure is the most useful of the three tested. For. Sci. 40(2):247-266.

Keywords: PPS sampling; Variable-radius-plot sampling

Document Type: Journal Article

Affiliations: College of Forestry and Wildlife Resources, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0324

Publication date: May 1, 1994

More about this publication?
  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
    Ranking: 16 of 66 in forestry

    Also published by SAF:
    Journal of Forestry
    Other SAF Publications
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