Health status assessment of tropical trees in Malay beechwood (Gmelina arborea Roxb.) plantation using electrical resistivity method and electrical impedance tomography

Health status assessment of tropical trees in Malay beechwood (Gmelina arborea Roxb.) plantation using electrical resistivity method and electrical impedance tomography | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Health status assessment of tropical trees in Malay beechwood ( Gmelina arborea Roxb.) plantation using electrical resistivity method and electrical impedance tomography Kayode Olaoye, Adewale Agbo-Adediran, Xiping Wang, Ayodele O. Soge, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5920801/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study investigates the tree health status of a Malay beechwood ( Gmelina arborea Roxb.) plantation using the non-destructive four-point electrical resistivity method and electrical impedance tomography (EIT). Twenty standing G. arborea trees (T1-T20) of different stem diameters were selected for evaluation. The electrical resistivities of the sampled trees were measured with varying current penetration and subjected to descriptive statistical analysis, analysis of variance (ANOVA), and correlation analysis. EIT tomograms were generated for three trees to corroborate the electrical resistivity findings. Subsequently, the trees were felled to inspect internal decay visually. Healthy trees exhibited a consistent pattern of increasing electrical resistivity from sapwood to heartwood, ranging between 58 Ωm and 1797 Ωm, while unhealthy trees, T1 and T6 were characterized by irregular electrical resistivity patterns with exorbitant mean values of 193,508 Ωm and 5,542 Ωm, respectively. Also, we found a negative significant correlation between stem diameters and electrical resistivity at the core stem. The ANOVA and follow-up test showed significant variability in the mean electrical resistivity of healthy trees. Trees T3 and T8, which exhibited lower mean electrical resistivity values of 157 Ωm and 183 Ωm, respectively, were determined to be healthier. The EIT tomograms and cross-sectional analyses of the felled trees corroborated the results obtained from the four-point electrical resistivity method. Forestry Malay beechwood trees non-destructive testing internal tree defects electrical resistivity method electrical impedance tomography Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction The quality of trees in forest plantations is critical to ensuring the production of high-quality wood products. Internal defects such as decay, cavities, and cracks significantly affect forest health and timber quality (De Petris et al., 2020 ; Papandrea et al., 2022 ). These defects not only reduce wood density but also diminish both the ecological and economic value of trees (Beall & Wilcox, 1987 ; Goncz et al., 2018 ). In urban environments, such internal defects compromise the structural stability of trees, posing safety risks (Papandrea et al., 2022 ; Santini et al., 2019 ). As forestry industries face increasing economic pressure to maximize value, evaluating tree vigor and forest stand health has become an essential aspect of sustainable forest management (Wang et al., 2007 ). Non-destructive testing (NDT) techniques offer a valuable approach for investigating internal tree defects without altering material properties (Dwivedi et al., 2018 ). These techniques enable early detection of issues such as wood decay, cavities, and cracks, even when external indicators are absent (Wang et al., 2004 ). NDT methods like stress wave analysis, acoustic tomography, and electrical resistivity have proven effective in ensuring wood quality and maintaining the structural integrity of trees in both urban and plantation settings. For example, Wei et al., ( 2022 ) used stress wave analysis to detect internal decay in Populus euphratica in China’s arid regions, achieving over 80% accuracy. Their study revealed correlations between decay, tree morphology, and water conditions, demonstrating the utility of this technique in diagnosing internal defects. Acoustic tomography has also been widely studied for its effectiveness. Mușat, ( 2023 ); Mușat et al., ( 2020 ) investigated fire-damaged spruce and lime trees, demonstrating how sound wave propagation and resistograph measurements complement each other in diagnosing internal defects. Similarly, Proto et al., ( 2020 ) showed that sonic tomography could accurately predict ring shake in chestnut trees, distinguishing between healthy and defective trees without compromising their biological activity. These examples underscore the role of NDT in identifying defects that traditional methods often miss. Electrical resistivity and electrical impedance tomography (EIT) are other advanced NDT techniques used to diagnose internal tree defects. These methods rely on measuring changes in electrical resistance caused by decay, as fungal activities increase ion concentrations in decayed wood. EIT, in particular, complements resistivity methods by generating detailed tomograms that reveal the internal structure of trees. The suitability of EIT to better detect brown and white rot fungi gave it a comparative advantage over acoustic methods (Olaoye & Ojo, 2022 ). Furthermore, studies have validated the effectiveness of these techniques in detecting early-stage decay in tropical species (Anderson, 1997 ; Gao et al., 2019 ; Larsson et al., 2004; Martin, 2009 ) such as with Terminalia catappa and Senna alata (Soge et al., 2018, 2019). The transformative potential of NDT methods to monitor tree health, detect defects, and support sustainable practices underscores the need for broader research, investment, and adoption, particularly in tropical forestry sectors in countries like Nigeria. These methods not only ensure the safety and productivity of urban and plantation trees but also maximize wood quality for industrial applications. However, in Nigeria, the adoption of NDT has been limited partly due to the lack of advanced equipment. Notwithstanding, studies have highlighted its potential for tropical forestry applications. Olaoye et al., ( 2021 ); Olaoye, ( 2019 ); Olaoye & Ojo, ( 2022 ); Olaoye & Okon-Akan, ( 2020 ) demonstrated the use of acoustic techniques for assessing wood quality in tropical trees, thus, emphasizing the relevance of NDT in commonly used Nigerian wood species. Also, A clinical test of the electrical resistivity method was performed on selected Nigerian wood species (Soge et al., 2018, 2019). However, these studies overlooked deeper current depths, did not utilize EIT for validation, and failed to consider its implementation in forest plantations. Notably, our preliminary surveys involving visual inspection of the Gmelina arborea plantation revealed significant wood decay, evidenced by dried wood, fallen leaves, and several fallen trees, suggesting that the prolonged activities of brown-rot fungi ( Poria cocos ) caused these trees to collapse. This poses a serious threat to the sustainability of the plantation Building on these efforts, we applied a hybrid approach of using the four-point electrical resistivity method and EIT in this study to assess the internal decay and salvage of the plantation, hence, providing critical insights for forest management. By integrating these resistivity methods to forestry practices, forest managers can mitigate risks, improve plantation sustainability, and enhance the long-term viability of forest ecosystems. Materials and Method Sampling Technique and Method We selected twenty Gmelina arborea standing trees from the Federal College of Forestry plantation, Ibadan, Southwest Nigeria, for this study. The selection included presumed healthy trees, which showed no visible signs of defects, and unhealthy trees, identified by visible indicators such as cracks, damaged bark, or the absence of a crown. The trees were tagged T1 to T20. Field Measurement We measured the electrical resistivity of the sampled Gmelina arborea trees using the four-point electrical resistivity method, as described by Larsson et al., (2004). The vertical variation of resistivity with depth was assessed using the Schlumberger electrode configuration on a reduced scale, following the approach outlined by Reynolds et al., ( 2006 ). For this measurement, we strategically positioned four electrodes along the length of the tree trunk: two current electrodes (C1 and C2) and two potential electrodes (P1 and P2). The current electrodes, separated by a distance AB, were used to introduce a direct current into the tree stem, while the potential electrodes, separated by a distance MN, were used to measure the potential difference between two points on the trunk (Figs. 1 and 2a). To ensure sufficient depth of current penetration, we used potential electrode separations of 4 cm, 6 cm, 8 cm, and 10 cm. Concurrently, the current electrode positions were varied incrementally between 4 cm and 50 cm at 2 cm intervals. This systematic approach enabled the investigation of the vertical resistivity profile of the tree trunk, providing insights into its internal structure. The separation of the current electrodes (AB) is generally proportional to the depth of current penetration (Herman, 2001 ). Therefore, an increase in electrode separation is expected to result in deeper current penetration. To minimize potential injuries to the tree stems and prevent short circuits, which are occasionally caused by conventional electrodes of 14 mm thickness, we used smaller electrodes with a thickness of 3.84 mm. Following the experimental setup illustrated in Fig. 2a, we measured the electrical resistance values \(\:{(R}_{a})\) of the G.arborea trees at various points using the Miller 400D digital resistance meter, commonly called an earth resistivity meter. Subsequently, the apparent resistivity values \(\:\left({\rho\:}_{a}\right)\) were calculated using Eq. 1. \(\:{\rho\:}_{a}={R}_{a}K\) 1 where K is the geometric factor K of the electrode configuration calculated using Eq. 2, \(\:K=2\pi\:{\left[\left(\frac{1}{AM}-\frac{1}{MB}\right)-\left(\frac{1}{AN}-\frac{1}{NB}\right)\right]}^{-1}\) 2 AM, MB, AN, and NB are the electrode separations as shown in Fig. 1 (Reynolds 2011). After screening the apparent resistivity values \(\:\left({\rho\:}_{a}\right)\) obtained using the resistivity meter, we subjected 3 trees, one presumed healthy and two suspected of having internal defects — to further validation through the EIT experiment. To conduct the EIT measurements, we inserted point-like electrodes (galvanized nails) around the circumference of the tree stem at breast height, as shown in Fig. 2b. These electrodes were connected to the EIT device, which injected a maximum current of 20 mA into the tree stem to determine the spatial resistance distribution across the stem cross-section. The electrical resistivity data collected from the EIT device were processed using the PiCUS Q74 Treetronic software application, which generated tomograms (resistivity images) representing the internal structure of the tree stem. The number of electrodes used for this experiment was based on the circumference of each tree. The diameter at breast height and at base was measured using the girthing tape. Afterward, we fell all sampled trees to visually inspect the extent of internal decay and validate the resistivity methods. Statistical analysis We subjected the electrical resistivity values obtained from the 20 selected trees to descriptive statistics. We used the Pearson correlation to determine the relationship between the stem diameters and mean resistivity values of the Gmelina arborea trees. Additionally, we performed an analysis of variance (ANOVA) to assess the statistical differences among the mean resistivity values of the sampled trees, and the potential electrode separation. Results Electrical resistivity Table 1 presents the minimum and maximum resistivity values, variance, range, and stem diameters for the examined trees. Tree T19 exhibited a minimum resistivity value of 59 Ωm, while tree T1 recorded a maximum resistivity value of 618,597 Ωm. Trees T1 and T6 exhibited exorbitantly higher resistivity range values of 602,361 Ωm and 75,797 Ωm, respectively, hence, we analyzed them separately. We suspected that the external defects in trees T1 and T6 (Fig. 3 a and Fig. 3 b) are evident for their irregular resistivity spikes (Fig. 5 ), The resistivity profiles of current electrode half-separation for trees T2, T3, T4, T5, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, and T20 were afterward displayed in Fig. 4 . The resistivity plots revealed a consistent pattern across the trees, showing a gradual increase in resistivity values from the sapwood to the heartwood. All the trees recorded resistivity values below 200 Ωm at the current electrode half-separation \(\:\left(\frac{AB}{2}\right)\) and MN of 4 cm, being the minimum depth of current penetration. Conversely, tree T18 had the highest resistivity of 1,797 Ωm at \(\:\frac{AB}{2}\) and MN of 50 cm and 10 cm, respectively (maximum depth of current penetration). Regarding stem diameters, trees T5 and T20 had the smallest diameter at breast height (25.14 cm) and at the base (31.35 cm), respectively while tree T15 had the largest diameter at breast height and base, measuring 71.93 cm and 81.51 cm, respectively. Furthermore, the analysis of variance (ANOVA) (Table 2 ) conducted for the remaining 18 trees revealed a significant difference in the mean resistivity values and interaction with potential electrode separation, hence, the follow-up test assisted us in grading the sampled trees according to their health status (Fig. 6 ). Notably, Pearson correlation analysis showed a negative significant correlation between the resistivity and stem diameters of the sampled trees at the core stem (MN = 10cm), with correlation coefficients of − 0.563 and − 0.551 for diameter at breast height and diameter at the base, respectively (Table 3 ) Electrical impedance tomography (EIT) Following the post hoc analysis of the resistivity profiles of the sampled trees, we purposefully subjected trees T3, T4, and T14, representing both presumed healthy and unhealthy trees to EIT validation. Our findings of the EIT tomograms along with the corresponding cross-sections of the trees after felling were presented in Fig. 7 to 9. Tree T3, identified as one of the healthiest samples, exhibited an EIT tomogram that shows a gradual increase in electrical resistance from the sapwood toward the heartwood or (core wood) (Fig. 7 a). In the tomogram, the blue regions indicate low electrical resistance values corresponding to the sapwood, while the red regions signify high resistance values associated with the heartwood. The cross-sectional photograph of tree T3 confirmed the absence of visible internal decay or hollows (Fig. 7 b). In contrast, the EIT tomogram of tree T4 (Fig. 8 a) reveals significant decay within the heartwood, indicated by the dominance of blue colouration, with the internal decay process gradually extending into the sapwood. The tomogram of tree T14, evidenced by the red color in its stem core (Fig. 9a), shows similarities with T3 (Fig. 7 a), particularly in the high electrical resistance values observed at its heartwood. However, the cross-section of the tree (Fig. 9b) confirms the presence of a hollow. Table 1 Resistivity values (Apparent) and tree diameters of the Gmelina arborea trees Trees Min. (Ωm) Max. (Ωm) Mean (Ωm) Variance (Ωm) Range (Ωm) S.E (Ωm) Dbh (cm) Db (cm) T1 16,236 618,597 193,509 3.42x10 10 602,361 37,763 28.01 32.78 T2 74 674 312 31,517 599 36 34.37 43.92 T3 79 299 157 4,668 219 14 50.60 57.29 T4 141 731 541 28,549 590 34 46.47 55.06 T5 102 1,556 660 195,828 1,454 90 25.14 33.10 T6 576 76,372 5,542 2.43x10 8 75,797 3,184 34.05 38.83 T7 58 605 318 26,741 547 33 45.51 56.97 T8 66 271 183 2,600 205 10 49.01 60.15 T9 81 535 290 17,839 454 27 47.10 58.24 T10 82 490 293 13,306 408 24 53.79 80.20 T11 60 664 348 29,705 604 35 41.69 54.42 T12 108 1,120 589 90,020 1,012 61 44.24 51.88 T13 92 538 285 14,029 445 24 34.69 43.60 T14 95 1,525 670 183,159 1,430 87 29.92 40.74 T15 62 503 295 15,914 440 26 71.93 81.51 T16 72 988 430 76,516 916 56 32.15 44.88 T17 60 502 297 14,190 442 24 47.74 60.31 T18 145 1,797 860 229,612 1,652 98 31.35 38.35 T19 59 567 301 22,339 508 31 50.60 59.74 T20 88 536 252 17,200 448 27 25.88 31.35 Min. – Minimum Max. – Maximum S.E. – Standard Error Dbh – Diameter at breast height Db – Diameter at the base Table 2 ANOVA showing the interaction between the resistivity and potential electrode separations (MN) of Gmelina arborea trees Source df Mean Square Sig. Tree 17 876705 0.001 MN 3 5063872 0.001 Tree * MN 51 123055.7 0.001 Error 360 5134.306 Total 431 * Significant at α 0.05 Table 3 Pearson Correlation between the mean resistivity values and the stem diameters of the sampled trees \(\:{\varvec{\rho\:}}_{\varvec{a}}\) Dbh Db Mean -0.476* -0.473* MN (4cm) -0.267ns -0.286ns MN (6cm) -0.288ns -0.302ns MN (8cm) -0.450ns -0.447ns MN (10cm) -0.563* -0.551* * Significant at α 0.05 Discussion Table 1 and Fig. 5 highlight that Trees T1 and T6 exhibit exorbitantly high and irregular resistivity patterns, with Fig. 3 confirming their unhealthy status due to visible external decay. Our findings agreed with those of Bieker & Rust, ( 2010 ) who evaluated the resistivity of sapwood and heartwood width in Scots pine ( Pinus sylvestris L.) trees and found a steep pattern of low and high resistivity values. Similarly, Soge et al., (2018, 2019), detected unhealthy trees through abrupt changes in resistivity, corresponding to decay and hollowing. Additionally, the gradual increase in resistivity from sapwood to heartwood observed in this study supports Fazriati et al., ( 2022 ), who documented similar trends in healthy Swietenia mahagoni and G. arborea . Similarly, Manyazawale & Ostrofsky, ( 1992 ) reported lower internal electrical resistance (IER) in sapwood compared to heartwood, with Guyot et al., ( 2013 ) noting lower resistivity in outer wood and higher resistivity in the inner wood of conifers. (Fazriati et al., 2022 ) attributed this trend to the higher moisture content in the sapwood of these trees. Notably, Smith & Shortle, ( 1988 ) posited that reduced electrical resistivity at the core wood indicates early decay, while cavities elevate resistivity due to their non-conductive nature (Larsson et al., 2004). In the same vein, Soge et al., (2019) claimed that hollows in trees can result in a large increase in the electrical resistivity values. These pieces of literature infer that healthy trees are identified by a consistent pattern of gradual increase in electrical resistivity from outer to core wood. Conversely, unhealthy trees have inconsistent variation in electrical resistivity from outer to core wood. Notably, in the core wood of unhealthy trees, low resistivity is associated with internal decay while steep high resistivity identifies with hollow. The results we obtained for the apparent resistivity suggest that except for T1 and T6, all trees are likely healthy. However, the significant differences in mean resistivity and its interaction with potential electrode separation, revealed by ANOVA, indicate variability in the trees' health. This was confirmed by the post-hoc analysis, hence, grading of the trees' healthiness as shown in Fig. 6 . For validation, three trees—presumed healthy (T3), fairly unhealthy (T4), and unhealthy (T14)—were assessed using Electrical Impedance Tomography (EIT). The tomograph in Fig. 7 a showing a colour gradient from blue to red towards the core, indicates a gradual resistivity increase from outer wood to core wood depicting tree T3 as healthy, as confirmed by the cross-section in Fig. 7 b. Hence, we confirm that the EIT validates our classification of tree T3 as healthy. In the same vein, we sort validation of tree T4 as unhealthy and found that the blue colouration is an indication of low resistivity due to decay from fungal activity (Fig. 8 a), as noted by Brazee et al., ( 2011 ); Soge et al., ( 2021 ). This explains the slight decline in its resistivity curve at \(\:\frac{AB}{2}\) = 26cm (Fig. 4 a). The decay is further evidenced by the cross-section in Fig. 8 b, confirming T4 as fairly unhealthy. Tree T14, despite being hollow, demonstrates higher electrical resistivity at the heartwood (indicated by red colouration), like the healthy tree T3. Smith & Shortle, ( 1988 ) linked high core resistivity to the presence of hollows or cavities, because hollows are non-conductive (Larsson et al., 2004). Nevertheless, we observed that T14 exhibits a more intense red colouration in a specific region compared to T3, signifying a higher mean resistivity. Thus, the elevated mean resistivity and pronounced red colouration in the EIT facilitate the identification of hollow trees. Finally, the negative correlation between stem diameter and mean resistivity indicates that G. arborea trees with wider stems exhibit lower resistivity, particularly in the core. This suggests that larger diameters may signal a higher risk of internal decay. These findings align with Wei et al., ( 2022 ), who reported a positive correlation between internal defects and stem diameter, which could be due to increased moisture or ion concentration from fungal activity (Soge et al., 2021 ). Conclusion In this study, we evaluated the health status of selected Gmelina arborea trees using the non-destructive electrical resistivity method and electrical impedance tomography (EIT). Our results indicated that healthy trees exhibit a consistent pattern of increasing electrical resistivity from the outer stem toward the core, whereas unhealthy trees show irregular variations in resistivity. The EIT validation confirmed that mean electrical resistivity is a reliable indicator for assessing tree health. Additionally, we found that G. arborea trees with larger stem diameters tend to have lower electrical resistivity, suggesting a higher susceptibility to internal decay. These findings underscore the effectiveness of electrical resistivity and EIT as non-destructive tools for detecting internal defects and comprehensively assessing tree health. Consequently, we recommend the application of these methods for routine monitoring of G. arborea plantations to support sustainable tree management practices. Declarations Funding This work was supported by the International Foundation for Science (IFS) under Grant [D-6641-1]. Disclosure statement The authors report that there are no competing interests to declare. References Anderson, S. (1997). Tree Diseases and Disorders: Causes, Biology, and Control in Forest and Amenity Trees. Heinz Butin , David Lonsdale , Robert Strouts . The Quarterly Review of Biology , 72 (2). https://doi.org/10.1086/419797 Beall, F. C., & Wilcox, W. W. (1987). RELATIONSHIP OF ACOUSTIC EMISSION DURING RADIAL COMPRESSION TO MASS LOSS FROM DECAY. Forest Products Journal , 37 (4). Bieker, D., & Rust, S. (2010). Non-destructive estimation of sapwood and heartwood width in scots pine (Pinus sylvestris L.). Silva Fennica , 44 (2). https://doi.org/10.14214/sf.153 Brazee, N. J., Marra, R. E., Göcke, L., & Van Wassenaer, P. (2011). Non-destructive assessment of internal decay in three hardwood species of northeastern North America using sonic and electrical impedance tomography. Forestry , 84 (1). https://doi.org/10.1093/forestry/cpq040 De Petris, S., Sarvia, F., & Borgogno-Mondino, E. (2020). RPAS-based photogrammetry to support tree stability assessment: Longing for precision arboriculture. Urban Forestry and Urban Greening , 55 . https://doi.org/10.1016/j.ufug.2020.126862 Dwivedi, S. K., Vishwakarma, M., & Soni, P. A. (2018). Advances and Researches on Non Destructive Testing: A Review. Materials Today: Proceedings , 5 (2). https://doi.org/10.1016/j.matpr.2017.11.620 Fazriati, E., Purnama, A., Algifari, G. A., Muslimah, I. S. A., Sumanto, F. H. P., Kirana, K. H., & Susanto, K. (2022). Cross-Section Resistivity Detection of Tree (Swietenia Magahoni and Gmelina) Using ERT Method. Jurnal Penelitian Pendidikan IPA , 8 (1), 39–44. https://doi.org/10.29303/jppipa.v8i1.965 Gao, S., Yue, X., & Wang, L. (2019). Effect of the degree of decay on the electrical resistance of wood degraded by brown-rot fungi. Canadian Journal of Forest Research , 49 (2). https://doi.org/10.1139/cjfr-2018-0282 Goncz, B., Divos, F., & Bejo, L. (2018). Detecting the presence of red heart in beech (Fagus sylvatica) using electrical voltage and resistance measurements. European Journal of Wood and Wood Products , 76 (2). https://doi.org/10.1007/s00107-017-1225-4 Guyot, A., Ostergaard, K. T., Lenkopane, M., Fan, J., & Lockington, D. A. (2013). Using electrical resistivity tomography to differentiate sapwood from heartwood: Application to conifers. Tree Physiology , 33 (2). https://doi.org/10.1093/treephys/tps128 Herman, R. (2001). An introduction to electrical resistivity in geophysics. American Journal of Physics , 69 (9). https://doi.org/10.1119/1.1378013 Larsson, B., Bengtsson, B., & Gustafsson, M. (2004a). Nondestructive detection of decay in living trees. Tree Physiology , 24 (7). https://doi.org/10.1093/treephys/24.7.853 Larsson, B., Bengtsson, B., & Gustafsson, M. (2004b). Nondestructive detection of decay in living trees. Tree Physiology , 24 (7). https://doi.org/10.1093/treephys/24.7.853 Manyazawale, B., & Ostrofsky, W. (1992). An assessment of internal decay of red spruce (picea rubenssarg.) using the shigometer . Martin, T. (2009). Complex resistivity (CR) of wood and standing trees. Non-Destructive Testing in Civil Engineering Conference . Mușat, E. C. (2023). The Agreement in Accuracy between Tomograms, Resistograms, and the Actual Condition of the Wood from Lime Trees Harvested from Cities. BioResources , 18 (1). https://doi.org/10.15376/biores.18.1.1757-1779 Mușat, E. C., Derczeni, R. A., Barti, M. E., & Dumitru-Dobre, C. (2020). Analysis of sound velocity through wood of spruce trees located into a burned area. FORESTRY BULLETIN , 24 (4), 98–109. https://doi.org/10.18698/2542-1468-2020-4-98-109 Olaoye, K., Aguda, L., & Ogunleye, B. (2021). Prediction of Mechanical Properties of Hardwood Species Using the Longitudinal Vibration Acoustic Method. Forest Products Journal , 71 (4), 391–400. https://doi.org/10.13073/fpj-d-21-00048 Olaoye, K. O. (2019). Investigation into the Determination of Modulus of Elasticity of Gmelina Arborea (Roxb.) Wood Using a Non-Destructive Acoustic Method. Pro Ligno , 15 (1), 11–16. Olaoye, K. O., & Ojo, M. O. (2022). Non-destructive acoustic assessment of wood quality in trees and logs and the effects of silvicultural treatments: a review. International Wood Products Journal , 13 (3), 156–171. https://doi.org/10.1080/20426445.2022.2061255 Olaoye, K., & Okon-Akan, O. A. (2020). Estimation of modulus of elasticity of Boscia angustifolia wood using longitudinal vibration acoustic method. International Wood Products Journal . https://doi.org/10.1080/20426445.2020.1738118 Papandrea, S. F., Cataldo, M. F., Zimbalatti, G., & Proto, A. R. (2022). Comparative evaluation of inspection techniques for decay detection in urban trees. Sensors and Actuators A: Physical , 340 . https://doi.org/10.1016/j.sna.2022.113544 Proto, A. R., Cataldo, M. F., Costa, C., Papandrea, S. F., & Zimbalatti, G. (2020). A tomographic approach to assessing the possibility of ring shake presence in standing chestnut trees. European Journal of Wood and Wood Products , 78 (6). https://doi.org/10.1007/s00107-020-01591-0 Reynolds, J. M., Durrant, D., Moy, T., Hutton, P., & Dussy, S. (2006). 2nd An Introduction to Applied and Environmental Geophysics. In John Wiley & Sons, Ltd. (Issue 606). Santini, L., Ortega Rodriguez, D. R., Quintilhan, M. T., Brazolin, S., & Tommasiello Filho, M. (2019). Evidence to wood biodeterioration of tropical species revealed by non-destructive techniques. Science of the Total Environment , 672 . https://doi.org/10.1016/j.scitotenv.2019.03.429 Smith, K. T., & Shortle, W. C. (1988). Electrical Resistance and Wood Decay by White Rot Fungi. Mycologia , 80 (1), 124–126. https://doi.org/10.1080/00275514.1988.12025510 Soge, A. O., Popoola, O., & Adetoyinbo, A. (2018a). Detection of decay and hollows in living almond trees (Terminalia catappa L. Roxb.) using electrical resistivity method. Journal of the Indian Academy of Wood Science , 15 (2), 181–189. https://doi.org/10.1007/s13196-018-0224-3 Soge, A. O., Popoola, O., & Adetoyinbo, A. (2018b). Detection of decay and hollows in living almond trees (Terminalia catappa L. Roxb.) using electrical resistivity method. Journal of the Indian Academy of Wood Science , 15 (2), 181–189. https://doi.org/10.1007/s13196-018-0224-3 Soge, A. O., Popoola, O. I., & Adetoyinbo, A. A. (2019a). A four-point electrical resistivity method for detecting wood decay and hollows in living trees. European Journal of Wood and Wood Products , 77 (3), 465–474. https://doi.org/10.1007/s00107-019-01402-1 Soge, A. O., Popoola, O. I., & Adetoyinbo, A. A. (2019b). A four-point electrical resistivity method for detecting wood decay and hollows in living trees. European Journal of Wood and Wood Products , 77 (3), 465–474. https://doi.org/10.1007/s00107-019-01402-1 Soge, A. O., Popoola, O. I., & Adetoyinbo, A. A. (2021). Detection of wood decay and cavities in living trees: A review. Canadian Journal of Forest Research , 51 (7), 937–947. https://doi.org/10.1139/cjfr-2020-0340 Wang, X., Carter, P., Ross, R. J., & Brashaw, B. K. (2007). Acoustic assessment of wood quality of raw forest materials - A path to increased profitability. In Forest Products Journal (Vol. 57, Issue 5, pp. 6–14). Wang, X. P., Divos, F., Pilon, C., Brashaw, B. K., Ross, R. J., & Pellerin, R. F. (2004). Assessment of decay in standing timber using stress wave timing nondestructive evaluation tools - a guide for use and interpretation. General Technical Report - Forest Products Laboratory, USDA Forest Service , 12 pp. Wei, Z., Halik, Ü., Aishan, T., Abliz, A., & Welp, M. (2022). Spatial distribution patterns of trunk internal decay of Euphrates poplar riparian forest along the Tarim River, northwest China. Forest Ecology and Management , 522 . https://doi.org/10.1016/j.foreco.2022.120434 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5920801","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":408358482,"identity":"615a2bdd-2862-481b-854b-e232cb57b949","order_by":0,"name":"Kayode Olaoye","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIiWNgGAWjYBACCRDxAESwNwAJAwsitSSACJ4DIC0SpGiRSIDz8QPJ9gbGBwk1Non9ks+vbvhRIMHA396dgFeLNM8BZoOEY2mJM2fnlN3sATpM4szZDXi1yEkksAHR4cQNt3PSbvAAtRhI5BKj5d/hxP03z6Td/EOMFmmQlsQ2oC0S7MduE2WLZM/BZoPEvjTjGWdy2G7LGEjwEPSLxPHmgw8+fLOR7W8//uzmmz82cvztvfi1MDAwNoBIxwYGHgMQg4eAcgSwB6aYB0SrHgWjYBSMgpEFANRhR49DpfL5AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-9808-2299","institution":"Federal College of Forestry, Forestry Research Institute of Nigeria, Jericho, Ibadan, Oyo State, Nigeria and USDA Forest Service, Forest Products Laboratory, WI, USA","correspondingAuthor":true,"prefix":"","firstName":"Kayode","middleName":"","lastName":"Olaoye","suffix":""},{"id":408360508,"identity":"bfb91b59-29d4-4169-b850-2b1871088c11","order_by":1,"name":"Adewale Agbo-Adediran","email":"","orcid":"","institution":"Federal College of Forestry, Forestry Research Institute of Nigeria, Jericho, Ibadan, Oyo State, Nigeria","correspondingAuthor":false,"prefix":"","firstName":"Adewale","middleName":"","lastName":"Agbo-Adediran","suffix":""},{"id":408360509,"identity":"d1dceb71-3b67-44fc-a7d0-dc1648cfe0d7","order_by":2,"name":"Xiping Wang","email":"","orcid":"","institution":"USDA Forest Service, Forest Products Laboratory, WI, USA","correspondingAuthor":false,"prefix":"","firstName":"Xiping","middleName":"","lastName":"Wang","suffix":""},{"id":408360510,"identity":"79b30be0-72c1-4da7-bd1e-ac5bfaff4dbc","order_by":3,"name":"Ayodele O. Soge","email":"","orcid":"","institution":"Department of Physical Sciences, Faculty of Natural Sciences, Redeemer’s University, Ede, Osun State, Nigeria","correspondingAuthor":false,"prefix":"","firstName":"Ayodele","middleName":"O.","lastName":"Soge","suffix":""},{"id":408360511,"identity":"ae4828f2-d214-4a4c-897d-2cd10ae69a1d","order_by":4,"name":"Kolawole Abodunrin","email":"","orcid":"","institution":"Federal College of Forestry, Forestry Research Institute of Nigeria, Jericho, Ibadan, Oyo State, Nigeria","correspondingAuthor":false,"prefix":"","firstName":"Kolawole","middleName":"","lastName":"Abodunrin","suffix":""},{"id":408360512,"identity":"0c1c0e82-0f4b-4010-9b50-ecac42eeaf66","order_by":5,"name":"Denis Adenuga","email":"","orcid":"","institution":"Federal College of Forestry, Forestry Research Institute of Nigeria, Jericho, Ibadan, Oyo State, Nigeria","correspondingAuthor":false,"prefix":"","firstName":"Denis","middleName":"","lastName":"Adenuga","suffix":""},{"id":408360513,"identity":"c601cf74-1bde-4bfe-bf78-9a6df90ad4d0","order_by":6,"name":"Samuel Ayankoso","email":"","orcid":"","institution":"Federal College of Forestry, Forestry Research Institute of Nigeria, Jericho, Ibadan, Oyo State, Nigeria","correspondingAuthor":false,"prefix":"","firstName":"Samuel","middleName":"","lastName":"Ayankoso","suffix":""}],"badges":[],"createdAt":"2025-01-28 20:36:02","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":true,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":true},"doi":"10.21203/rs.3.rs-5920801/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5920801/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":75074223,"identity":"2a3c91a3-2499-4fbb-b71a-9f36364f2d63","added_by":"auto","created_at":"2025-01-30 07:43:05","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":75299,"visible":true,"origin":"","legend":"\u003cp\u003eGeneral electrode configuration for resistivity measurement. \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e and C\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e represent the current electrodes while P\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e and P\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e are the potential electrodes. MN, AM, MB, AN, NB, and AB are the electrode separations. AB represents the current electrode separation while MN is the potential electrode separation.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/f7baa6e29e09151c447c61d7.png"},{"id":75073419,"identity":"3722587f-2683-48e2-bb59-f83e325258b2","added_by":"auto","created_at":"2025-01-30 07:35:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1008280,"visible":true,"origin":"","legend":"\u003cp\u003eField set-up of the electrical resistivity methods: \u003cstrong\u003e(a)\u003c/strong\u003e Four electrodes (two current electrodes C1, C2, and two potential electrodes P1, and P2) are arranged along the length of the tree trunk and connected with metal clips to the earth resistivity meter; \u003cstrong\u003e(b)\u003c/strong\u003e Electrical impedance tomography measurement using PICUS Treetronic 3 with the electrodes inserted at breast height around the entire circumference of the tree.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/4691e507dd775a466ff337d0.png"},{"id":75074225,"identity":"73ea1fff-bc8f-4cb5-91b3-d279cc0be343","added_by":"auto","created_at":"2025-01-30 07:43:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":520212,"visible":true,"origin":"","legend":"\u003cp\u003eUnhealthy stands of \u003cem\u003eG. arborea\u003c/em\u003e trees: (a) T1 and (b) T6, with visual evidence of external defects: cracks, damaged bark, and no crown.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/f03be2bdf0caf27aedcd5115.png"},{"id":75074224,"identity":"4e174417-d079-4753-9e25-cf82aba0f54c","added_by":"auto","created_at":"2025-01-30 07:43:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":95621,"visible":true,"origin":"","legend":"\u003cp\u003eElectrical resistivity plots of Gmelina arborea trees: (a) Trees T2, T3, T4, T5, T7, T8, T9, T10 and T11; (b) trees T12, T13, T14, T15, T16, T17, T18, T19 and T20.\u003c/p\u003e\n\u003cp\u003eMN – Potential Electrode separations = 4cm, 6cm, 8cm and 10cm\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/ab2fc0c1d65a477d3c55022a.png"},{"id":75074893,"identity":"7cf3645e-51db-478f-85bc-5878f4bc96ce","added_by":"auto","created_at":"2025-01-30 07:51:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":99504,"visible":true,"origin":"","legend":"\u003cp\u003eElectrical resistivity plots of \u003cem\u003eGmelina arborea\u003c/em\u003e trees T1 and T6\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/15acdd991149657e8a47cc14.png"},{"id":75073441,"identity":"163ccf5a-3536-4926-af64-e59f87d54a7b","added_by":"auto","created_at":"2025-01-30 07:35:06","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":27943,"visible":true,"origin":"","legend":"\u003cp\u003eHealth grading of the 18 \u003cem\u003eGmelina arborea \u003c/em\u003etrees showing nine subsets significant at α\u003csub\u003e0.05\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/141f04bdc51d48bc5d829eb9.png"},{"id":75074888,"identity":"b96797a4-2ca2-47ce-92b3-a593c79010c6","added_by":"auto","created_at":"2025-01-30 07:51:06","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":643976,"visible":true,"origin":"","legend":"\u003cp\u003eHealthy \u003cem\u003eGmelina arborea\u003c/em\u003e tree (T3): (a) Electrical Impedance Tomogram: The blue colour represents low values of electrical resistance (sapwood) while the red colour represents high values of electrical resistance (heartwood); (b) A cross-section of the stem after cutting shows no visual\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/c5b9b3fad8f02242e02dcedf.png"},{"id":75073432,"identity":"b5823b14-86fb-4411-887f-dc1e0d63fc9c","added_by":"auto","created_at":"2025-01-30 07:35:06","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":809326,"visible":true,"origin":"","legend":"\u003cp\u003eDecayed \u003cem\u003eGmelina arborea\u003c/em\u003e tree (T4): (a) Electrical Impedance Tomogram: The blue colour represents low values of electrical resistance (decayed heartwood) while the yellow and red colours represent high values of electrical resistance (healthy region of the sapwood). (b) A cross-section of the decayed tree trunk after felling.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/8adfec0e6913dfb667546aa4.png"},{"id":75073431,"identity":"957dd19a-f207-407a-b807-927d5dc46402","added_by":"auto","created_at":"2025-01-30 07:35:06","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1043258,"visible":true,"origin":"","legend":"\u003cp\u003eHollowed \u003cem\u003eGmelina arborea\u003c/em\u003e tree (T14): (a) The blue colour represents low values of electrical resistance (sapwood) while the red colour represents comparatively high values of electrical resistance (hollow heartwood); (b) A cross-section of the stem after cutting showing visual evidence of hollow at the core stem.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/fade88a99a28eb47f1394186.png"},{"id":75076305,"identity":"6850606b-3cd6-4eb1-b42f-9709a7628d13","added_by":"auto","created_at":"2025-01-30 07:59:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5899192,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5920801/v1/78d13cdf-e0ee-4ee4-bfa4-a817044c0b1d.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eHealth status assessment of tropical trees in Malay beechwood (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eGmelina arborea \u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eRoxb.) plantation using electrical resistivity method and electrical impedance tomography\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe quality of trees in forest plantations is critical to ensuring the production of high-quality wood products. Internal defects such as decay, cavities, and cracks significantly affect forest health and timber quality (De Petris et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Papandrea et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These defects not only reduce wood density but also diminish both the ecological and economic value of trees (Beall \u0026amp; Wilcox, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Goncz et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In urban environments, such internal defects compromise the structural stability of trees, posing safety risks (Papandrea et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Santini et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). As forestry industries face increasing economic pressure to maximize value, evaluating tree vigor and forest stand health has become an essential aspect of sustainable forest management (Wang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNon-destructive testing (NDT) techniques offer a valuable approach for investigating internal tree defects without altering material properties (Dwivedi et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). These techniques enable early detection of issues such as wood decay, cavities, and cracks, even when external indicators are absent (Wang et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). NDT methods like stress wave analysis, acoustic tomography, and electrical resistivity have proven effective in ensuring wood quality and maintaining the structural integrity of trees in both urban and plantation settings. For example, Wei et al., (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) used stress wave analysis to detect internal decay in \u003cem\u003ePopulus euphratica\u003c/em\u003e in China\u0026rsquo;s arid regions, achieving over 80% accuracy. Their study revealed correlations between decay, tree morphology, and water conditions, demonstrating the utility of this technique in diagnosing internal defects.\u003c/p\u003e \u003cp\u003eAcoustic tomography has also been widely studied for its effectiveness. Mușat, (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e); Mușat et al., (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) investigated fire-damaged spruce and lime trees, demonstrating how sound wave propagation and resistograph measurements complement each other in diagnosing internal defects. Similarly, Proto et al., (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) showed that sonic tomography could accurately predict ring shake in chestnut trees, distinguishing between healthy and defective trees without compromising their biological activity. These examples underscore the role of NDT in identifying defects that traditional methods often miss.\u003c/p\u003e \u003cp\u003eElectrical resistivity and electrical impedance tomography (EIT) are other advanced NDT techniques used to diagnose internal tree defects. These methods rely on measuring changes in electrical resistance caused by decay, as fungal activities increase ion concentrations in decayed wood. EIT, in particular, complements resistivity methods by generating detailed tomograms that reveal the internal structure of trees. The suitability of EIT to better detect brown and white rot fungi gave it a comparative advantage over acoustic methods (Olaoye \u0026amp; Ojo, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Furthermore, studies have validated the effectiveness of these techniques in detecting early-stage decay in tropical species (Anderson, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Gao et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Larsson et al., 2004; Martin, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) such as with \u003cem\u003eTerminalia catappa\u003c/em\u003e and \u003cem\u003eSenna alata\u003c/em\u003e (Soge et al., 2018, 2019).\u003c/p\u003e \u003cp\u003eThe transformative potential of NDT methods to monitor tree health, detect defects, and support sustainable practices underscores the need for broader research, investment, and adoption, particularly in tropical forestry sectors in countries like Nigeria. These methods not only ensure the safety and productivity of urban and plantation trees but also maximize wood quality for industrial applications.\u003c/p\u003e \u003cp\u003eHowever, in Nigeria, the adoption of NDT has been limited partly due to the lack of advanced equipment. Notwithstanding, studies have highlighted its potential for tropical forestry applications. Olaoye et al., (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e); Olaoye, (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); Olaoye \u0026amp; Ojo, (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e); Olaoye \u0026amp; Okon-Akan, (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) demonstrated the use of acoustic techniques for assessing wood quality in tropical trees, thus, emphasizing the relevance of NDT in commonly used Nigerian wood species. Also, A clinical test of the electrical resistivity method was performed on selected Nigerian wood species (Soge et al., 2018, 2019). However, these studies overlooked deeper current depths, did not utilize EIT for validation, and failed to consider its implementation in forest plantations.\u003c/p\u003e \u003cp\u003eNotably, our preliminary surveys involving visual inspection of the \u003cem\u003eGmelina arborea\u003c/em\u003e plantation revealed significant wood decay, evidenced by dried wood, fallen leaves, and several fallen trees, suggesting that the prolonged activities of brown-rot fungi (\u003cem\u003ePoria cocos\u003c/em\u003e) caused these trees to collapse. This poses a serious threat to the sustainability of the plantation\u003c/p\u003e \u003cp\u003eBuilding on these efforts, we applied a hybrid approach of using the four-point electrical resistivity method and EIT in this study to assess the internal decay and salvage of the plantation, hence, providing critical insights for forest management. By integrating these resistivity methods to forestry practices, forest managers can mitigate risks, improve plantation sustainability, and enhance the long-term viability of forest ecosystems.\u003c/p\u003e"},{"header":"Materials and Method","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eSampling Technique and Method\u003c/h2\u003e\n \u003cp\u003eWe selected twenty \u003cem\u003eGmelina arborea\u003c/em\u003e standing trees from the Federal College of Forestry plantation, Ibadan, Southwest Nigeria, for this study. The selection included presumed healthy trees, which showed no visible signs of defects, and unhealthy trees, identified by visible indicators such as cracks, damaged bark, or the absence of a crown. The trees were tagged T1 to T20.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eField Measurement\u003c/h3\u003e\n\u003cp\u003eWe measured the electrical resistivity of the sampled \u003cem\u003eGmelina arborea\u003c/em\u003e trees using the four-point electrical resistivity method, as described by Larsson et al., (2004). The vertical variation of resistivity with depth was assessed using the Schlumberger electrode configuration on a reduced scale, following the approach outlined by Reynolds et al., (\u003cspan class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eFor this measurement, we strategically positioned four electrodes along the length of the tree trunk: two current electrodes (C1 and C2) and two potential electrodes (P1 and P2). The current electrodes, separated by a distance AB, were used to introduce a direct current into the tree stem, while the potential electrodes, separated by a distance MN, were used to measure the potential difference between two points on the trunk (Figs. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e and 2a).\u003c/p\u003e\n\u003cp\u003eTo ensure sufficient depth of current penetration, we used potential electrode separations of 4 cm, 6 cm, 8 cm, and 10 cm. Concurrently, the current electrode positions were varied incrementally between 4 cm and 50 cm at 2 cm intervals. This systematic approach enabled the investigation of the vertical resistivity profile of the tree trunk, providing insights into its internal structure.\u003c/p\u003e\n\u003cp\u003eThe separation of the current electrodes (AB) is generally proportional to the depth of current penetration (Herman, \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e). Therefore, an increase in electrode separation is expected to result in deeper current penetration. To minimize potential injuries to the tree stems and prevent short circuits, which are occasionally caused by conventional electrodes of 14 mm thickness, we used smaller electrodes with a thickness of 3.84 mm.\u003c/p\u003e\n\u003cp\u003eFollowing the experimental setup illustrated in Fig. 2a, we measured the electrical resistance values \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{(R}_{a})\\)\u003c/span\u003e\u003c/span\u003e of the \u003cem\u003eG.arborea\u003c/em\u003e trees at various points using the Miller 400D digital resistance meter, commonly called an earth resistivity meter. Subsequently, the apparent resistivity values \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left({\\rho\\:}_{a}\\right)\\)\u003c/span\u003e\u003c/span\u003e were calculated using Eq. 1.\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{a}={R}_{a}K\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e 1\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere K is the geometric factor K of the electrode configuration calculated using Eq.\u0026nbsp;2,\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:K=2\\pi\\:{\\left[\\left(\\frac{1}{AM}-\\frac{1}{MB}\\right)-\\left(\\frac{1}{AN}-\\frac{1}{NB}\\right)\\right]}^{-1}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e 2\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eAM, MB, AN, and NB are the electrode separations as shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (Reynolds 2011).\u003c/p\u003e\n\u003cp\u003eAfter screening the apparent resistivity values \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left({\\rho\\:}_{a}\\right)\\)\u003c/span\u003e\u003c/span\u003e obtained using the resistivity meter, we subjected 3 trees, one presumed healthy and two suspected of having internal defects \u0026mdash; to further validation through the EIT experiment. To conduct the EIT measurements, we inserted point-like electrodes (galvanized nails) around the circumference of the tree stem at breast height, as shown in Fig. 2b. These electrodes were connected to the EIT device, which injected a maximum current of 20 mA into the tree stem to determine the spatial resistance distribution across the stem cross-section. The electrical resistivity data collected from the EIT device were processed using the PiCUS Q74 Treetronic software application, which generated tomograms (resistivity images) representing the internal structure of the tree stem. The number of electrodes used for this experiment was based on the circumference of each tree. The diameter at breast height and at base was measured using the girthing tape.\u003c/p\u003e\n\u003cp\u003eAfterward, we fell all sampled trees to visually inspect the extent of internal decay and validate the resistivity methods.\u003c/p\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003eStatistical analysis\u003c/h2\u003e\n \u003cp\u003eWe subjected the electrical resistivity values obtained from the 20 selected trees to descriptive statistics. We used the Pearson correlation to determine the relationship between the stem diameters and mean resistivity values of the \u003cem\u003eGmelina arborea\u003c/em\u003e trees. Additionally, we performed an analysis of variance (ANOVA) to assess the statistical differences among the mean resistivity values of the sampled trees, and the potential electrode separation.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003eElectrical resistivity\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e presents the minimum and maximum resistivity values, variance, range, and stem diameters for the examined trees. Tree T19 exhibited a minimum resistivity value of 59 Ωm, while tree T1 recorded a maximum resistivity value of 618,597 Ωm. Trees T1 and T6 exhibited exorbitantly higher resistivity range values of 602,361 Ωm and 75,797 Ωm, respectively, hence, we analyzed them separately. We suspected that the external defects in trees T1 and T6 (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea and Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb) are evident for their irregular resistivity spikes (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e),\u003c/p\u003e\n \u003cp\u003eThe resistivity profiles of current electrode half-separation for trees T2, T3, T4, T5, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, and T20 were afterward displayed in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. The resistivity plots revealed a consistent pattern across the trees, showing a gradual increase in resistivity values from the sapwood to the heartwood. All the trees recorded resistivity values below 200 Ωm at the current electrode half-separation \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left(\\frac{AB}{2}\\right)\\)\u003c/span\u003e\u003c/span\u003e and MN of 4 cm, being the minimum depth of current penetration. Conversely, tree T18 had the highest resistivity of 1,797 Ωm at \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{AB}{2}\\)\u003c/span\u003e\u003c/span\u003e and MN of 50 cm and 10 cm, respectively (maximum depth of current penetration).\u003c/p\u003e\n \u003cp\u003eRegarding stem diameters, trees T5 and T20 had the smallest diameter at breast height (25.14 cm) and at the base (31.35 cm), respectively while tree T15 had the largest diameter at breast height and base, measuring 71.93 cm and 81.51 cm, respectively.\u003c/p\u003e\n \u003cp\u003eFurthermore, the analysis of variance (ANOVA) (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) conducted for the remaining 18 trees revealed a significant difference in the mean resistivity values and interaction with potential electrode separation, hence, the follow-up test assisted us in grading the sampled trees according to their health status (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). Notably, Pearson correlation analysis showed a negative significant correlation between the resistivity and stem diameters of the sampled trees at the core stem (MN\u0026thinsp;=\u0026thinsp;10cm), with correlation coefficients of \u0026minus;\u0026thinsp;0.563 and \u0026minus;\u0026thinsp;0.551 for diameter at breast height and diameter at the base, respectively (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eElectrical impedance tomography (EIT)\u003c/h3\u003e\n\u003cp\u003eFollowing the post hoc analysis of the resistivity profiles of the sampled trees, we purposefully subjected trees T3, T4, and T14, representing both presumed healthy and unhealthy trees to EIT validation. Our findings of the EIT tomograms along with the corresponding cross-sections of the trees after felling were presented in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e to 9. Tree T3, identified as one of the healthiest samples, exhibited an EIT tomogram that shows a gradual increase in electrical resistance from the sapwood toward the heartwood or (core wood) (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea). In the tomogram, the blue regions indicate low electrical resistance values corresponding to the sapwood, while the red regions signify high resistance values associated with the heartwood. The cross-sectional photograph of tree T3 confirmed the absence of visible internal decay or hollows (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb).\u003c/p\u003e\n\u003cp\u003eIn contrast, the EIT tomogram of tree T4 (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea) reveals significant decay within the heartwood, indicated by the dominance of blue colouration, with the internal decay process gradually extending into the sapwood. The tomogram of tree T14, evidenced by the red color in its stem core (Fig. 9a), shows similarities with T3 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea), particularly in the high electrical resistance values observed at its heartwood. However, the cross-section of the tree (Fig. 9b) confirms the presence of a hollow.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eResistivity values (Apparent) and tree diameters of the \u003cem\u003eGmelina arborea\u003c/em\u003e trees\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTrees\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMin. (Ωm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMax.\u003c/p\u003e\n \u003cp\u003e(Ωm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean (Ωm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVariance (Ωm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRange (Ωm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS.E\u003c/p\u003e\n \u003cp\u003e(Ωm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDbh (cm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDb (cm)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16,236\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e618,597\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e193,509\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.42x10\u003csup\u003e10\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e602,361\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37,763\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e32.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e674\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e312\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31,517\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e599\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43.92\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e299\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e157\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4,668\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e219\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e57.29\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e731\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e541\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28,549\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e590\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e46.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e55.06\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e102\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,556\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e660\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e195,828\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,454\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e576\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e76,372\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5,542\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.43x10\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75,797\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3,184\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e605\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e318\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26,741\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e547\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e45.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56.97\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e271\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e183\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2,600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e205\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e49.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60.15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e535\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e290\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17,839\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e454\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e47.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e58.24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e490\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e293\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13,306\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e408\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e53.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e80.20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e664\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e348\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29,705\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e604\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e41.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e54.42\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e108\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,120\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e589\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90,020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.88\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e538\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e285\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14,029\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e445\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43.60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,525\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e670\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e183,159\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,430\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.74\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e503\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e295\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15,914\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e440\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e988\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e430\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e76,516\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e916\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e32.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.88\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e502\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e297\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14,190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e442\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e47.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60.31\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e145\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,797\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e860\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e229,612\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1,652\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e567\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e301\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22,339\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e508\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.74\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e536\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e252\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17,200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e448\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eMin. \u0026ndash; Minimum \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Max. \u0026ndash; Maximum\u0026nbsp;\u003cbr\u003eS.E. \u0026ndash; Standard Error \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Dbh \u0026ndash; Diameter at breast height\u0026nbsp;\u003cbr\u003eDb \u0026ndash; Diameter at the base\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eANOVA showing the interaction between the resistivity and potential electrode separations (MN) of \u003cem\u003eGmelina arborea\u003c/em\u003e trees\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSource\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003edf\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean Square\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSig.\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTree\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e876705\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5063872\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTree * MN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e123055.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eError\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e360\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5134.306\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e431\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\"\u003e* Significant at \u0026alpha;\u003csub\u003e0.05\u003c/sub\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePearson Correlation between the mean resistivity values and the stem diameters of the sampled trees\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{\\rho\\:}}_{\\varvec{a}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDbh\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDb\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.476*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.473*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMN (4cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.267ns\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.286ns\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMN (6cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.288ns\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.302ns\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMN (8cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.450ns\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.447ns\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMN (10cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.563*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.551*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\"\u003e* Significant at \u0026alpha;\u003csub\u003e0.05\u003c/sub\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e highlight that Trees T1 and T6 exhibit exorbitantly high and irregular resistivity patterns, with Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e confirming their unhealthy status due to visible external decay. Our findings agreed with those of Bieker \u0026amp; Rust, (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) who evaluated the resistivity of sapwood and heartwood width in Scots pine (\u003cem\u003ePinus sylvestris\u003c/em\u003e L.) trees and found a steep pattern of low and high resistivity values. Similarly, Soge et al., (2018, 2019), detected unhealthy trees through abrupt changes in resistivity, corresponding to decay and hollowing.\u003c/p\u003e \u003cp\u003eAdditionally, the gradual increase in resistivity from sapwood to heartwood observed in this study supports Fazriati et al., (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), who documented similar trends in healthy \u003cem\u003eSwietenia mahagoni\u003c/em\u003e and \u003cem\u003eG. arborea\u003c/em\u003e. Similarly, Manyazawale \u0026amp; Ostrofsky, (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1992\u003c/span\u003e) reported lower internal electrical resistance (IER) in sapwood compared to heartwood, with Guyot et al., (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) noting lower resistivity in outer wood and higher resistivity in the inner wood of conifers. (Fazriati et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) attributed this trend to the higher moisture content in the sapwood of these trees.\u003c/p\u003e \u003cp\u003eNotably, Smith \u0026amp; Shortle, (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1988\u003c/span\u003e) posited that reduced electrical resistivity at the core wood indicates early decay, while cavities elevate resistivity due to their non-conductive nature (Larsson et al., 2004). In the same vein, Soge et al., (2019) claimed that hollows in trees can result in a large increase in the electrical resistivity values.\u003c/p\u003e \u003cp\u003eThese pieces of literature infer that healthy trees are identified by a consistent pattern of gradual increase in electrical resistivity from outer to core wood. Conversely, unhealthy trees have inconsistent variation in electrical resistivity from outer to core wood. Notably, in the core wood of unhealthy trees, low resistivity is associated with internal decay while steep high resistivity identifies with hollow.\u003c/p\u003e \u003cp\u003eThe results we obtained for the apparent resistivity suggest that except for T1 and T6, all trees are likely healthy. However, the significant differences in mean resistivity and its interaction with potential electrode separation, revealed by ANOVA, indicate variability in the trees' health. This was confirmed by the post-hoc analysis, hence, grading of the trees' healthiness as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e. For validation, three trees\u0026mdash;presumed healthy (T3), fairly unhealthy (T4), and unhealthy (T14)\u0026mdash;were assessed using Electrical Impedance Tomography (EIT).\u003c/p\u003e \u003cp\u003eThe tomograph in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ea showing a colour gradient from blue to red towards the core, indicates a gradual resistivity increase from outer wood to core wood depicting tree T3 as healthy, as confirmed by the cross-section in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003eb. Hence, we confirm that the EIT validates our classification of tree T3 as healthy. In the same vein, we sort validation of tree T4 as unhealthy and found that the blue colouration is an indication of low resistivity due to decay from fungal activity (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003ea), as noted by Brazee et al., (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2011\u003c/span\u003e); Soge et al., (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This explains the slight decline in its resistivity curve at \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{AB}{2}\\)\u003c/span\u003e\u003c/span\u003e = 26cm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The decay is further evidenced by the cross-section in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003eb, confirming T4 as fairly unhealthy.\u003c/p\u003e \u003cp\u003eTree T14, despite being hollow, demonstrates higher electrical resistivity at the heartwood (indicated by red colouration), like the healthy tree T3. Smith \u0026amp; Shortle, (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1988\u003c/span\u003e) linked high core resistivity to the presence of hollows or cavities, because hollows are non-conductive (Larsson et al., 2004). Nevertheless, we observed that T14 exhibits a more intense red colouration in a specific region compared to T3, signifying a higher mean resistivity. Thus, the elevated mean resistivity and pronounced red colouration in the EIT facilitate the identification of hollow trees.\u003c/p\u003e \u003cp\u003eFinally, the negative correlation between stem diameter and mean resistivity indicates that \u003cem\u003eG. arborea\u003c/em\u003e trees with wider stems exhibit lower resistivity, particularly in the core. This suggests that larger diameters may signal a higher risk of internal decay. These findings align with Wei et al., (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), who reported a positive correlation between internal defects and stem diameter, which could be due to increased moisture or ion concentration from fungal activity (Soge et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, we evaluated the health status of selected Gmelina arborea trees using the non-destructive electrical resistivity method and electrical impedance tomography (EIT). Our results indicated that healthy trees exhibit a consistent pattern of increasing electrical resistivity from the outer stem toward the core, whereas unhealthy trees show irregular variations in resistivity. The EIT validation confirmed that mean electrical resistivity is a reliable indicator for assessing tree health. Additionally, we found that \u003cem\u003eG. arborea\u003c/em\u003e trees with larger stem diameters tend to have lower electrical resistivity, suggesting a higher susceptibility to internal decay.\u003c/p\u003e \u003cp\u003eThese findings underscore the effectiveness of electrical resistivity and EIT as non-destructive tools for detecting internal defects and comprehensively assessing tree health. Consequently, we recommend the application of these methods for routine monitoring of \u003cem\u003eG. arborea\u003c/em\u003e plantations to support sustainable tree management practices.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the International Foundation for Science (IFS) under Grant\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e[D-6641-1].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDisclosure statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors report that there are no competing interests to declare.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAnderson, S. (1997). Tree Diseases and Disorders: Causes, Biology, and Control in Forest and Amenity Trees. Heinz Butin , David Lonsdale , Robert Strouts . \u003cem\u003eThe Quarterly Review of Biology\u003c/em\u003e, \u003cem\u003e72\u003c/em\u003e(2). https://doi.org/10.1086/419797\u003c/li\u003e\n \u003cli\u003eBeall, F. C., \u0026amp; Wilcox, W. W. (1987). RELATIONSHIP OF ACOUSTIC EMISSION DURING RADIAL COMPRESSION TO MASS LOSS FROM DECAY. \u003cem\u003eForest Products Journal\u003c/em\u003e, \u003cem\u003e37\u003c/em\u003e(4).\u003c/li\u003e\n \u003cli\u003eBieker, D., \u0026amp; Rust, S. (2010). Non-destructive estimation of sapwood and heartwood width in scots pine (Pinus sylvestris L.). \u003cem\u003eSilva Fennica\u003c/em\u003e, \u003cem\u003e44\u003c/em\u003e(2). https://doi.org/10.14214/sf.153\u003c/li\u003e\n \u003cli\u003eBrazee, N. J., Marra, R. E., G\u0026ouml;cke, L., \u0026amp; Van Wassenaer, P. (2011). Non-destructive assessment of internal decay in three hardwood species of northeastern North America using sonic and electrical impedance tomography. \u003cem\u003eForestry\u003c/em\u003e, \u003cem\u003e84\u003c/em\u003e(1). https://doi.org/10.1093/forestry/cpq040\u003c/li\u003e\n \u003cli\u003eDe Petris, S., Sarvia, F., \u0026amp; Borgogno-Mondino, E. (2020). RPAS-based photogrammetry to support tree stability assessment: Longing for precision arboriculture. \u003cem\u003eUrban Forestry and Urban Greening\u003c/em\u003e, \u003cem\u003e55\u003c/em\u003e. https://doi.org/10.1016/j.ufug.2020.126862\u003c/li\u003e\n \u003cli\u003eDwivedi, S. K., Vishwakarma, M., \u0026amp; Soni, P. A. (2018). Advances and Researches on Non Destructive Testing: A Review. \u003cem\u003eMaterials Today: Proceedings\u003c/em\u003e, \u003cem\u003e5\u003c/em\u003e(2). https://doi.org/10.1016/j.matpr.2017.11.620\u003c/li\u003e\n \u003cli\u003eFazriati, E., Purnama, A., Algifari, G. A., Muslimah, I. S. A., Sumanto, F. H. P., Kirana, K. H., \u0026amp; Susanto, K. (2022). Cross-Section Resistivity Detection of Tree (Swietenia Magahoni and Gmelina) Using ERT Method. \u003cem\u003eJurnal Penelitian Pendidikan IPA\u003c/em\u003e, \u003cem\u003e8\u003c/em\u003e(1), 39\u0026ndash;44. https://doi.org/10.29303/jppipa.v8i1.965\u003c/li\u003e\n \u003cli\u003eGao, S., Yue, X., \u0026amp; Wang, L. (2019). Effect of the degree of decay on the electrical resistance of wood degraded by brown-rot fungi. \u003cem\u003eCanadian Journal of Forest Research\u003c/em\u003e, \u003cem\u003e49\u003c/em\u003e(2). https://doi.org/10.1139/cjfr-2018-0282\u003c/li\u003e\n \u003cli\u003eGoncz, B., Divos, F., \u0026amp; Bejo, L. (2018). Detecting the presence of red heart in beech (Fagus sylvatica) using electrical voltage and resistance measurements. \u003cem\u003eEuropean Journal of Wood and Wood Products\u003c/em\u003e, \u003cem\u003e76\u003c/em\u003e(2). https://doi.org/10.1007/s00107-017-1225-4\u003c/li\u003e\n \u003cli\u003eGuyot, A., Ostergaard, K. T., Lenkopane, M., Fan, J., \u0026amp; Lockington, D. A. (2013). Using electrical resistivity tomography to differentiate sapwood from heartwood: Application to conifers. \u003cem\u003eTree Physiology\u003c/em\u003e, \u003cem\u003e33\u003c/em\u003e(2). https://doi.org/10.1093/treephys/tps128\u003c/li\u003e\n \u003cli\u003eHerman, R. (2001). An introduction to electrical resistivity in geophysics. \u003cem\u003eAmerican Journal of Physics\u003c/em\u003e, \u003cem\u003e69\u003c/em\u003e(9). https://doi.org/10.1119/1.1378013\u003c/li\u003e\n \u003cli\u003eLarsson, B., Bengtsson, B., \u0026amp; Gustafsson, M. (2004a). Nondestructive detection of decay in living trees. \u003cem\u003eTree Physiology\u003c/em\u003e, \u003cem\u003e24\u003c/em\u003e(7). https://doi.org/10.1093/treephys/24.7.853\u003c/li\u003e\n \u003cli\u003eLarsson, B., Bengtsson, B., \u0026amp; Gustafsson, M. (2004b). Nondestructive detection of decay in living trees. \u003cem\u003eTree Physiology\u003c/em\u003e, \u003cem\u003e24\u003c/em\u003e(7). https://doi.org/10.1093/treephys/24.7.853\u003c/li\u003e\n \u003cli\u003eManyazawale, B., \u0026amp; Ostrofsky, W. (1992). \u003cem\u003eAn assessment of internal decay of red spruce (picea rubenssarg.) using the shigometer\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eMartin, T. (2009). Complex resistivity (CR) of wood and standing trees. \u003cem\u003eNon-Destructive Testing in Civil Engineering Conference\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eMușat, E. C. (2023). The Agreement in Accuracy between Tomograms, Resistograms, and the Actual Condition of the Wood from Lime Trees Harvested from Cities. \u003cem\u003eBioResources\u003c/em\u003e, \u003cem\u003e18\u003c/em\u003e(1). https://doi.org/10.15376/biores.18.1.1757-1779\u003c/li\u003e\n \u003cli\u003eMușat, E. C., Derczeni, R. A., Barti, M. E., \u0026amp; Dumitru-Dobre, C. (2020). Analysis of sound velocity through wood of spruce trees located into a burned area. \u003cem\u003eFORESTRY BULLETIN\u003c/em\u003e, \u003cem\u003e24\u003c/em\u003e(4), 98\u0026ndash;109. https://doi.org/10.18698/2542-1468-2020-4-98-109\u003c/li\u003e\n \u003cli\u003eOlaoye, K., Aguda, L., \u0026amp; Ogunleye, B. (2021). Prediction of Mechanical Properties of Hardwood Species Using the Longitudinal Vibration Acoustic Method. \u003cem\u003eForest Products Journal\u003c/em\u003e, \u003cem\u003e71\u003c/em\u003e(4), 391\u0026ndash;400. https://doi.org/10.13073/fpj-d-21-00048\u003c/li\u003e\n \u003cli\u003eOlaoye, K. O. (2019). Investigation into the Determination of Modulus of Elasticity of Gmelina Arborea (Roxb.) Wood Using a Non-Destructive Acoustic Method. \u003cem\u003ePro Ligno\u003c/em\u003e, \u003cem\u003e15\u003c/em\u003e(1), 11\u0026ndash;16.\u003c/li\u003e\n \u003cli\u003eOlaoye, K. O., \u0026amp; Ojo, M. O. (2022). Non-destructive acoustic assessment of wood quality in trees and logs and the effects of silvicultural treatments: a review. \u003cem\u003eInternational Wood Products Journal\u003c/em\u003e, \u003cem\u003e13\u003c/em\u003e(3), 156\u0026ndash;171. https://doi.org/10.1080/20426445.2022.2061255\u003c/li\u003e\n \u003cli\u003eOlaoye, K., \u0026amp; Okon-Akan, O. A. (2020). Estimation of modulus of elasticity of Boscia angustifolia wood using longitudinal vibration acoustic method. \u003cem\u003eInternational Wood Products Journal\u003c/em\u003e. https://doi.org/10.1080/20426445.2020.1738118\u003c/li\u003e\n \u003cli\u003ePapandrea, S. F., Cataldo, M. F., Zimbalatti, G., \u0026amp; Proto, A. R. (2022). Comparative evaluation of inspection techniques for decay detection in urban trees. \u003cem\u003eSensors and Actuators A: Physical\u003c/em\u003e, \u003cem\u003e340\u003c/em\u003e. https://doi.org/10.1016/j.sna.2022.113544\u003c/li\u003e\n \u003cli\u003eProto, A. R., Cataldo, M. F., Costa, C., Papandrea, S. F., \u0026amp; Zimbalatti, G. (2020). A tomographic approach to assessing the possibility of ring shake presence in standing chestnut trees. \u003cem\u003eEuropean Journal of Wood and Wood Products\u003c/em\u003e, \u003cem\u003e78\u003c/em\u003e(6). https://doi.org/10.1007/s00107-020-01591-0\u003c/li\u003e\n \u003cli\u003eReynolds, J. M., Durrant, D., Moy, T., Hutton, P., \u0026amp; Dussy, S. (2006). 2nd An Introduction to Applied and Environmental Geophysics. In \u003cem\u003eJohn Wiley \u0026amp; Sons, Ltd.\u003c/em\u003e (Issue 606).\u003c/li\u003e\n \u003cli\u003eSantini, L., Ortega Rodriguez, D. R., Quintilhan, M. T., Brazolin, S., \u0026amp; Tommasiello Filho, M. (2019). Evidence to wood biodeterioration of tropical species revealed by non-destructive techniques. \u003cem\u003eScience of the Total Environment\u003c/em\u003e, \u003cem\u003e672\u003c/em\u003e. https://doi.org/10.1016/j.scitotenv.2019.03.429\u003c/li\u003e\n \u003cli\u003eSmith, K. T., \u0026amp; Shortle, W. C. (1988). Electrical Resistance and Wood Decay by White Rot Fungi. \u003cem\u003eMycologia\u003c/em\u003e, \u003cem\u003e80\u003c/em\u003e(1), 124\u0026ndash;126. https://doi.org/10.1080/00275514.1988.12025510\u003c/li\u003e\n \u003cli\u003eSoge, A. O., Popoola, O., \u0026amp; Adetoyinbo, A. (2018a). Detection of decay and hollows in living almond trees (Terminalia catappa L. Roxb.) using electrical resistivity method. \u003cem\u003eJournal of the Indian Academy of Wood Science\u003c/em\u003e, \u003cem\u003e15\u003c/em\u003e(2), 181\u0026ndash;189. https://doi.org/10.1007/s13196-018-0224-3\u003c/li\u003e\n \u003cli\u003eSoge, A. O., Popoola, O., \u0026amp; Adetoyinbo, A. (2018b). Detection of decay and hollows in living almond trees (Terminalia catappa L. Roxb.) using electrical resistivity method. \u003cem\u003eJournal of the Indian Academy of Wood Science\u003c/em\u003e, \u003cem\u003e15\u003c/em\u003e(2), 181\u0026ndash;189. https://doi.org/10.1007/s13196-018-0224-3\u003c/li\u003e\n \u003cli\u003eSoge, A. O., Popoola, O. I., \u0026amp; Adetoyinbo, A. A. (2019a). A four-point electrical resistivity method for detecting wood decay and hollows in living trees. \u003cem\u003eEuropean Journal of Wood and Wood Products\u003c/em\u003e, \u003cem\u003e77\u003c/em\u003e(3), 465\u0026ndash;474. https://doi.org/10.1007/s00107-019-01402-1\u003c/li\u003e\n \u003cli\u003eSoge, A. O., Popoola, O. I., \u0026amp; Adetoyinbo, A. A. (2019b). A four-point electrical resistivity method for detecting wood decay and hollows in living trees. \u003cem\u003eEuropean Journal of Wood and Wood Products\u003c/em\u003e, \u003cem\u003e77\u003c/em\u003e(3), 465\u0026ndash;474. https://doi.org/10.1007/s00107-019-01402-1\u003c/li\u003e\n \u003cli\u003eSoge, A. O., Popoola, O. I., \u0026amp; Adetoyinbo, A. A. (2021). Detection of wood decay and cavities in living trees: A review. \u003cem\u003eCanadian Journal of Forest Research\u003c/em\u003e, \u003cem\u003e51\u003c/em\u003e(7), 937\u0026ndash;947. https://doi.org/10.1139/cjfr-2020-0340\u003c/li\u003e\n \u003cli\u003eWang, X., Carter, P., Ross, R. J., \u0026amp; Brashaw, B. K. (2007). Acoustic assessment of wood quality of raw forest materials - A path to increased profitability. In \u003cem\u003eForest Products Journal\u003c/em\u003e (Vol. 57, Issue 5, pp. 6\u0026ndash;14).\u003c/li\u003e\n \u003cli\u003eWang, X. P., Divos, F., Pilon, C., Brashaw, B. K., Ross, R. J., \u0026amp; Pellerin, R. F. (2004). Assessment of decay in standing timber using stress wave timing nondestructive evaluation tools - a guide for use and interpretation. \u003cem\u003eGeneral Technical Report - Forest Products Laboratory, USDA Forest Service\u003c/em\u003e, 12 pp.\u003c/li\u003e\n \u003cli\u003eWei, Z., Halik, \u0026Uuml;., Aishan, T., Abliz, A., \u0026amp; Welp, M. (2022). Spatial distribution patterns of trunk internal decay of Euphrates poplar riparian forest along the Tarim River, northwest China. \u003cem\u003eForest Ecology and Management\u003c/em\u003e, \u003cem\u003e522\u003c/em\u003e. https://doi.org/10.1016/j.foreco.2022.120434\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"a7e48bcb-015a-43ef-9fd1-2d7fd6dc2734","identifier":"10.13039/501100001724","name":"International Foundation for Science","awardNumber":"D-6641-1","order_by":0}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Federal College of Forestry, Forestry Research Institute of Nigeria, Jericho, Ibadan, Oyo State, Nigeria","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Malay beechwood trees, non-destructive testing, internal tree defects, electrical resistivity method, electrical impedance tomography ","lastPublishedDoi":"10.21203/rs.3.rs-5920801/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5920801/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the tree health status of a Malay beechwood (\u003cem\u003eGmelina arborea\u003c/em\u003e Roxb.) plantation using the non-destructive four-point electrical resistivity method and electrical impedance tomography (EIT). Twenty standing \u003cem\u003eG. arborea\u003c/em\u003etrees (T1-T20) of different stem diameters were selected for evaluation. The electrical resistivities of the sampled trees were measured with varying current penetration and subjected to descriptive statistical analysis, analysis of variance (ANOVA), and correlation analysis. EIT tomograms were generated for three trees to corroborate the electrical resistivity findings. Subsequently, the trees were felled to inspect internal decay visually. Healthy trees exhibited a consistent pattern of increasing electrical resistivity from sapwood to heartwood, ranging between 58 Ωm and 1797 Ωm, while unhealthy trees, T1 and T6 were characterized by irregular electrical resistivity patterns with exorbitant mean values of 193,508 Ωm and 5,542 Ωm, respectively. Also, we found a negative significant correlation between stem diameters and electrical resistivity at the core stem. The ANOVA and follow-up test showed significant variability in the mean electrical resistivity of healthy trees. Trees T3 and T8, which exhibited lower mean electrical resistivity values of 157 Ωm and 183 Ωm, respectively, were determined to be healthier. The EIT tomograms and cross-sectional analyses of the felled trees corroborated the results obtained from the four-point electrical resistivity method.\u003c/p\u003e","manuscriptTitle":"Health status assessment of tropical trees in Malay beechwood (Gmelina arborea Roxb.) plantation using electrical resistivity method and electrical impedance tomography","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-30 07:35:00","doi":"10.21203/rs.3.rs-5920801/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ad9efd7a-bb1b-44d1-80d2-cafb33961859","owner":[],"postedDate":"January 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":43542503,"name":"Forestry"}],"tags":[],"updatedAt":"2025-01-30T07:35:01+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-30 07:35:00","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5920801","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5920801","identity":"rs-5920801","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}