Electrical resistivity imaging of tree trunks

Abstract

An electrical resistivity technique using a ring array of needle electrodes is applied to image the internal electrical structures of the trunks of living standing trees and trunk disks. Measured electrical resistance data are inverted using a 2D iterative finite-element algorithm which incorporates the cylindrical geometry of the trunk. The technique is successfully tested using synthetic models showing that the resolution obtained when mapping anomalous zones inside the trunk is higher for the dipole-dipole configuration than for the Wenner configuration. Measurements on a trunk column show a well-established inverse relationship between the imaged resistivity and the moisture content determined from wood cores.Healthy tree trunks always show a concentric ring structure with a central maximum of resistivity, which decreases towards the outside, corresponding to an increase in moisture from the inner dry heartwood to the outer wet ring of sapwood. Asymmetry in the ring structure is interpreted as the influence of branching or the direction of sunshine and wind. Strong local resistivity anomalies are related to infections causing wet, rotting or dry cavities. The resistivity of the heartwood is a maximum in olive and oak trunks, intermediate in young fruit trees and a minimum in cork oak trunks that are considered to be wet. The resistivity imaging technique can also monitor the dynamic process of sapflow if adequate tracers are used.

Quantifying sapwood width for three Australian native species using electrical resistivity tomography

“…Increasing the number of electrodes can increase the resolution of inversion results (al Hagrey ). Ideally, the spacing between each two adjacent electrodes should be smaller than the actual sapwood width (Guyot et al ., ).…”

“…Electrical resistivity for one selected tree of each species is given in Figure . The same typical R s spatial distribution pattern is observed for each tree as illustrated by al Hagrey (), that is, high R s in the trunk centre (heartwood) decreasing toward the outer layers (sapwood and wet bark). These trees have different diameters, which can be observed from the axes.…”

Detection of buried tree root samples by using geoelectrical measurements: a laboratory experiment

“…Electrical resistivity tomography using multi-electrode arrays on the surface or in small boreholes can be successfully applied to generate images of root zones reflecting their spatial variability and to quantify their biomass (Amato et al 2008;Amato et al 2009;Petersen and Al-Hagrey 2009) or to study the water flow in soil and plants (Pagès et al 2000). Other applications of electrical resistivity tomography using ring electrode arrays around a trunk aim at a detailed investigation of living trees (Al-Hagrey 2006;Nicolotti et al 2003;Weihs et al 1999). The resulting horizontal cross-sections of the conductivity distribution can be used to monitor the sap flow and to recognise decay processes in the trunk.…”

Effects of lightning on trees: A predictive model based on in situ electrical resistivity

“…Like Stamm (), we found that wood moisture content can supersede species identity as a determinant of electrical resistivity. Although the important role of moisture in wood resistivity is well established (Al Hagrey, ; Carter & Blanchard, ; Gora & Yanoviak, ), no other studies have compared moisture‐resistivity patterns among growth forms or trees in situ.…”