Personal Bias in Forest Measurements

The assumption that measurement errors are negligible during a forest inventory was tested using forestry students. The magnitude of personal bias in measuring tree diameter at breast height (dbh), total height, and basal area per hectare was obtained. Bias was negligible in dbh measurements and the among-crew coefficient of variation (CV) was 8.16%. Heights were significantly underestimated and the among-crew CV was 21.86%. The percentage error in basal area per hectare determination was 4.09% at the 95% probability level, using a prism of basal area factor 6. Measurement errors are, in general, not negligible. Their magnitude should be estimated per inventory and included in the total error of the inventory estimate.