Reliability of Rotfinder instrument for detecting decay in standing trees

Abstract: A wood decay detecting instrument, Rotfinder® was evaluated for its accuracy, sensitivity and specificity in detecting decay in standing trees. Five hundred trees were measured in three different stands with Rotfinder at three heights in the stems. The trees were felled and sectioned, and presence or absence of decay was observed for each section. Wood samples were taken from every section and their wood density and moisture content was measured. Rotfinder accuracy of detecting both decayed and healthy trees was 82.7%. The highest sensitivity was obtained at stump height (55.9%). Advanced decay was detected in the 71% of cases while incipient decay was detected in the 23% of cases. Rotfinder has a scale from 0 to 10 which indicates an increasing degree of probability of decay. Rotfinder values higher than 4 indicated more than 90% of probability of finding decay. Rotfinder successful detections (true positives and true negatives) and Rotfinder failures (false positives and false negatives) were compared in terms of moisture content, wood density and N, C, Mg, Ca, K, Na and Mn concentration. True positives had higher moisture content in reaction zone and decay, higher density in reaction zone and higher concentration of calcium and sodium of reaction zone than false negatives. Relationship between Rotfinder values and wood characteristics were studied, and the potassium concentration showed the highest correlation with Rotfinder values.