Evaluation of the Barr & Stroud FP15 and Criterion 400 laser dendrometers for measuring upper stem diameters and heights

Calibrated Barr & Stroud FP15 and Criterion 400 laser dendrometers were tes ted for reliability in measuring upper stem diameters and heights under typ ical field conditions, Data were collected in the Black Hills National Fore st, which covers parts of South Dakota and Wyoming in the United States. Mi xed effects models were employed to account for differences between users o f the dendrometers and to test for significant differences between the heig hts and diameters measured indirectly (by dendrometer) and directly (by cal iper and linear tape). The location at which measurements were taken on eac h tree was determined by paint marks along the bole, No significant differe nces between users were found. The Barr & Stroud consistently overestimated diameters by approximately 0.3 cm (0.1 in), Unbiased estimates of diameter were obtained with the Criterion 400. For height measurements, neither the Barr & Stroud nor the Criterion 400 produced unbiased measurements. The ef fect of distance to the base of the tree and height of the diameter measure ment on the variability of the measurements was also studied. As distance i ncreased, the variability of diameter measurements increased for both dendr ometers. For the measurement of height, only the Barr & Stroud exhibited an increase in the variability of measurements with increasing distance. Afte r correcting the data for their biases, taper equations were fitted to them and analyzed. The equations generated from the Barr & Stroud were not sign ificantly different from those generated from direct measurement, unlike th e Criterion 400 where taper equations generated were statistically differen t. A brief study of the effects of familiarity with each dendrometer indica ted that the measurement error and variability decreased as the user became more familiar with the Criterion, This was not the case for the Barr & Str oud.