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Evaluation of Fine Root Length and Diameter Measurements Obtained Using RHIZO Image Analysis

Dep. of Forestry, Australian Natl. Univ., Canberra, ACT 0200, Australia
Forest Biology Section, P.O. Box 9519 Stn. Prov. Govt., Victoria, BC V8W 9C2, Canada [thereafter: Groupe de Recherche en Ècologie Forestière (GREF) interuniversitaire, Dép. des Sciences Biologiques, Univ. du Québec à Montréal, C.P. 8888, succursale centre ville, Montréal, QC H3C 3P8, Canada]

^* Corresponding author (christian.messier{at}gems5.gov.bc.ca through July 1999; thereafter: messier.christian{at}uqam.ca)

Image analysis systems facilitate rapid measurement of root length and diameter, but their accuracy is not easily delermined. The objective of this study was to develop a set of simple experiments for evaluating lhe accuracy of fine root measuremenls obtained using image analysis. Using the system RHIZO (trademark of Régent Instruments, Québec), we tested the accuracy of (i) length measurements made over a range of root lengths per unit area, (it) average diameter measurements and length per diameter distributions in string, wire, and fine root samples of varying diameter, and (iii) diameter measurements on short segments of diagonally oriented objecls. Our results suggest that preliminary lesting of image analysis syslems is absolutely necessary for producing reliable rool measurements. Total length was accurately determined for typically encountered length per unit areas of <1.5 cm cm^–2. For samples with higher values, however, the method underestimated total length by >>5%. It is therefore recommended that users of image analysis syslems determine this maximum length per unit area for accurate delerminations of total root length. In samples that contained differenl string diamelers, the total sample length and average string diameter could accurately be measured. However, the length per diameler class was underestimated by >20% when the string diameter was less lhan one pixel smaller than the upper limit of the diameter class. Adjustment of diameter intervals and increasing the scanner resolution are required to reduce this underestimalion. Both the length and the angle of the short segments analyzed were found lo influence diameter measurements. Similar sets of experiments are proposed for a rigorous evalualion of the performance of other image analysis systems on root measurements.

Received for publication August 28, 1997.

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