Electrical Resistance Tomography as a Non-Destructive Technique for Heartwood Detection and Quantification in Standing Red Sanders (Pterocarpus santalinus L.f.) Trees

Accurate, simple, cost-effective, and non-destructive estimation of heartwood content is essential for the sustainable management and commercial valuation of Pterocarpus santalinus L.f. (red sanders), one of the world’s most valuable tropical timber species. Conventional methods for heartwood assessment, including increment coring and destructive sampling, are invasive, time-consuming, and unsuitable for large-scale field applications. Electrical Resistance Tomography (ERT) offers a promising alternative by exploiting differences in electrical resistivity associated with variations in wood moisture content and anatomical characteristics. The present study standardized the application of ERT for the identification and quantification of heartwood in standing red sanders trees and validated its performance against conventional core sampling. Fifty-eight trees representing two diameter classes (10–20 cm and 20–30 cm) were evaluated using a PiCUS TreeTronic Electrical Resistance Tomograph, followed by increment core extraction at breast height for validation. Distinct resistivity gradients were observed, with higher electrical resistivity in the central heartwood region and lower resistivity in the peripheral sapwood. The resistivity values ranged from 153 to 1031 Ω in trees with diameters of 10–20 cm and from 342 to 1444 Ω in trees with diameters of 20–30 cm. Linear regression analysis showed excellent agreement between ERT-estimated and measured heartwood diameters (R2 = 0.98), with an average similarity of 91.5%. The observed resistivity distribution closely reflected variations in moisture content, wood density, and anatomical structure across the stem radius. The findings demonstrate that ERT is a reliable and non-destructive technique for estimating heartwood content in standing red sanders trees. These results demonstrate that ERT can accurately estimate heartwood dimensions in standing Pterocarpus santalinus trees under the conditions of the present study and provide a reliable approach for non-destructive assessment of heartwood in this species. The technique has considerable potential for timber valuation, harvest planning, tree breeding, forest inventory, and conservation programs involving high-value tropical hardwood species.