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5 International Scientific Online Conference DOI: https://doi.org/10.15414/2021.9788055224015

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NATURALLY OCCURRING DIRECT CURRENT IN TREES AS THE OVERALL TREE VITALITY
INDICATOR
Marek Kobza, Radovan Ostrovský
Institute of Forest Ecology of the Slovak Academy of Sciences, Department of Plant Pathology and
Mycology Nitra, Slovakia; E-mail.: marek.kobza@ife.sk
The aim of the work was the vitality evaluation of trees in urban greenery by the method
of the direct current measurement. Naturally occurring direct current (geo-phyto electrical
current) running between an entire tree and the earth was measured. The measurable intensity
of the current makes it possible to determine the health state of the tree with great precision,
starting from the onset of their physiological weakening, before the appearance of the first
external visible symptoms of the disease. The intensity of the direct current is “species-specific”
worldwide, depending on trunk diameter, active canopy area, and other parameters (weather
condition, temperature, and humidity).
Variation of measured current was determined periodically every four weeks during the
research period from January 2015 to December 2017. In the territory of city Nitra, a total of 44
visually healthy trees of various trunk diameters of four species (Pinus sylvestris, Fraxinus
excelsior, Betula pendula, Platanus x hispanica) were included in the trial. During the
measurement, maximal values of direct current and voltage between cambial tissue and the
earth were determined using a standard multimeter and inox probes, one penetrated trunk base
(1–3 cm deep) and the second penetrated approx. 0.3 m deep into the soil in the distance of
approximately 5 m from the tree.
Based on the measured data, trees were divided into five groups according to maximal
current divided by the diameter of the tree trunk (C/D). The highest C/D values, the better the
health state of the tree. The maximum values for completely healthy trees of each examined
species examined were used as a basis for comparison (100%). The reduction of this value by
various influences coincides regularly with a deterioration in the health state of the tree. During
the three-year growing period of trial, the highest currents were recorded from 24 to the 39
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week of the year. During this period, the highest currents were recorded for Scots pine 87 µA,
for European ash 281 µA, for Silver birch 265 µA, and London Plane tree 377 µA. Minimal values
were recorded during winter for all evaluated species.
Measurement of direct current is a fast, economical, and reliable method for the relatively
precise determination of tree vitality; however, further research of all parameters influencing
this current in trees is necessary.
Keywords: direct current, tree vitality, health state of tree, urban greenery.

Acknowledgments
The authors would like to thank Alena Magušinová for her help during fieldwork. This research was
funded by the Scientific Grant Agency of the Ministry of Education of the Slovak Republic and of the
Slovak Academy of Sciences, grant number VEGA 2/0062/18 and VEGA 2/0077/18.

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5 International Scientific Conference Agrobiodiversity for Improving the Nutrition, Health, Quality of Life and |79
Spiritual Human Development
November 3 2021
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