Minimum tree height sample sizes necessary for accurately estimating merchantable plot volume in Loblolly pine plantations

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Virginia Tech


The minimum number of tree heights that are necessary, with a probability of 0.95, to obtain a merchantable plot volume estimate of loblolly pine within ± 3, 5, and 10% of the volume observed if all plot trees had been measured for height were determined for all combinations of volume estimation techniques and sample designs examined in this study.

The volume estimation techniques examined in this study were:

  1. a volume equation using measured tree diameters and either measured heights or height estimates obtained from a plot height-diameter relationship,

  2. a volume equation using strata average diameter and average height, and\

  3. a strata volume/basal area ratio estimator.

The examined sampling designs were:

  1. a simple random sample,
  2. a stratified random sample,
  3. a stratified systematic sample, and
  4. a purposive sample. Both combined and separate stratified estimators were used for volume estimation techniques 2 and 3 when a stratified sample design was used.

Of all the possible combinations of volume estimation techniques and sample designs, two combinations, volume estimation technique 1 and a stratified random sample, and volume estimation technique 1 and a purposive sample, are the only combinations that have sample sizes of no more than 30 trees for all three accuracy levels and require the smallest or nearly the smallest number of sample tree heights at these accuracy levels.