Abstract: [Objective] Electric resistance tomography, stress wave imaging and resistograph were employed to detect and quantitatively characterize the internal decay for standing trees,then these three NDT(nondestructive testing)techniques were made comparisons in order to find out the appropriate technique matched with specific condition of standing trees in the forest field.[Method] An investigation about the accuracy of different NDT methods was carried out in the experiment forest of Northeast Forestry University in Harbin, Heilongjiang Province. 100 cross-sections of Fraxinus mandshurica and Populus×beijingensis standing trees were tested by four methods:electric resistance tomography, stress wave tomography, resistograph and estimation weight loss ratios of wooden increment cores. Taking wood core samples as research objects, testing results of three other kinds of NDT methods were compared. E_s determined by estimating weight loss ratios of wooden cores was regarded as the truth value of decay extent. Using ordinary least square regression to analyze the relationship between E_s and E_d(degree of decay determined by electric resistance tomography),E_s and E_y(degree of decay determined by stress wave),E_s and E_z(degree of decay determined by resistograph).[Result] Results showed that three NDT methods were able to estimate the different degree of decay for Fraxinus mandshurica and Populus×beijingensis standing trees; As a whole, the fitting degree of E_d and E_s, E_y and E_s were both lower than that of E_z and E_s. In different decay degree, when E_s<30%, E_d had a strong positive correlation with E_s(R=0.823,P<0.01), while when 30%≤E_s<50%, E_y have a significant positive correlation relationship with E_s(R=0.658,P<0.01), electric resistance tomography had more sensitively reflect in incipient decay of standing trees, and stress wave had more accurate diagnosis on detecting middle decay of standing tress. E_z had a strong positive correlation relationship with E_s, and when E_s≥50%, E_z have a more positive correlation relationship with E_s(R=0.914,P<0.01).[Conclusion] Electric resistance tomography showed better diagnosis than the other two methods for incipient decay of standing trees, while stress wave imaging method used in the middle stage of decay testing was best, and resistograph can be used in the different stages of decay. It was suggested that each technique could be employed in the practical internal decay testing for standing trees according to the decay stage and operational conditions.

Key words: mass loss rate, electric resistance tomography, velocity of stress wave, wood core resistance loss, decay extent