Determination of sapwood area in Pinus nigra by electrical impedance tomography

Since the life of a tree strongly depends on sapwood area activity, the detection and thickness measurement of sapwood area in living trees are important for forest scientists. However, determination of sapwood zones has various challenges in different species. In this research, the electrical impedance tomography was applied to calculate sapwood-heartwood ratio and electrical impedance variations in the given area in one of the most important softwood species (Pinus nigra). A GeoPic-32 multielectrode resistivity meter with some modifications, was used to measure electric impedance distribution in two heights of 147 and 200 cm of 8 pine tree cross sections in Sopron of Hungary. For providing tomograms, a 5-voltage electrical current was conducted among installed electrodes. The impedance value maps on the studied cross sections were also measured by a resistometer device. The tomography map showed that the role of sapwood area for electricity conductivity, compared with heartwood, was more pronounced. For all achieved tomograms, three zones with different colored pattern were detected. The red colored parts surrounding pith area had the highest values while the minimum resistivity values with the dark blue color, were recorded for area near the bark.  9 percentage difference in moisture content between sapwood and heartwood, pH variation (4.52˃3.88) and consequently different quantities in chemical components affected electrical properties distribution in cross section of trees. But potassium content had no pronounced effect on tomogram patterns obtained.  Finally, this technique is suggested to evaluate trees in forest because of facility, shortening of time, and minor destruction as well as no necessity to cut the tree.