Electrical resistivity tomography: patterns in Betula pendula, Fagus sylvatica, Picea abies and Pinus sylvestris.

Electrical resistivity (ER) tomography is a promising technique to minimally invasively study stems of living trees. It allows insights into xylem properties based on the cross-sectional distribution of ER that is governed by the wood's electrical conductance. In this study, ER measurements were carried out on four forest tree species, Betula pendula, Fagus sylvatica, Picea abies and Pinus sylvestris, to demonstrate interspecific, intraspecific and within-tree variation of ER tomograms. Further, ER patterns were linked to xylem moisture content (MC), electrolyte content and density obtained from wood core analyses. The ER patterns of both coniferous species, P. abies and P. sylvestris, were found to be more homogenous and concentric compared with the complex tomograms of angiosperms. However, the ER range of coniferous trees showed considerable intraspecific variation. Measurements near ground level showed pronounced effects on ER tomograms, highlighting the importance of the chosen measurement height. A strong relation between ER and wood density was found in F. sylvatica while ER patterns of conifers were mainly influenced by MC. Results demonstrate a high species specificity of ER tomograms and of respective influencing xylem traits. They underline the importance of reference measurements for a correct interpretation of ER studies.