Electric resistivity tomography shows radial variation of electrolytes in Quercus robur

Electric resistivity tomograms of English oak ( Quercus robur L.) show a very distinct pattern of electric resistivity that has not been found in any other tree species yet and that cannot be related to the distribution of wood moisture content over the stem cross section. To reveal the factors underlying this two-dimensional pattern of electric resistivity, the variation of specific gravity and wood moisture content was analyzed in 18 cross sections of six roadside English oak trees after electric resistivity tomography. pH and electrolyte content were analyzed in two representative cross sections. Results show that electric resistivity correlates neither with wood moisture content nor density. The steep increase in electric resistivity at the sapwood–heartwood boundary correlates well with decreasing pH, potassium, and magnesium. The decreasing electric resistivity within the heartwood of English oak correlates with potassium and magnesium, increasing from the sapwood–heartwood boundary to the pith. More research is needed to identify species-specific electric resistivity patterns and their main factors if the method is to be used to detect wood fungal decay, historical ground water contamination, or other influences that may change the pattern of electric resistivity in the stem cross section.