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SUMMARY
Two field trials of plantation inventory were carried out using interpenetrating subsamples to enable testing for measurement bias. One trial compared two experienced field crews in each of three different strata in the 1951 planting year of maritime pine at Gnangara plantation in Western Australia. The other was based on a comparison of an experienced and an inexperienced field crew in the 1933 planting year at Darkin plantation.
Measurement bias was negligible in relation to the volume per hectare of all trees in the inventory plots.
At Gnangara bias was apparent in the estimates of volume and basal area of the trees selected by the respective inventory crews for thinning. This probably reflects differences in interpretation or application of the thinning prescriptions. Bias was also apparent for height intercept, a measure of site index, but the source of this bias is not known.
There was no bias apparent between the experienced and inexperienced crews at Darkin for the volume or basal area of trees selected for thinning, or for height intercept.
The procedure outlined in this study can easily be incorporated in any forest inventory using random sampling. Provided two or more crews are working from the same base, measurement bias can be assessed at negligible extra cost.