András Koppán, Márta Kis Geodetic and Geophysical Research Institute, Earth Science Centre of the Hungarian Academy of Sciences, H-9400 Sopron, Csatkai u. 6-8. Sándor Szalai, László Szarka, Viktor Wesztergom University of West-Hungary, Institute for Geosciences, H-9400 Sopron, Csatkai u. 608.
ABSTRACT
Electrical potentials of natural origin have been studied in standing trees for several years. Voltage is measured by means of non-polarising electrodes, positioned at different heights and directions in the trunk. Characteristic time variations correlated with physiological functions have been found such as daily, seasonally, yearly etc. [1], [3], [4], [5]. A comparison with a direct sap-flow measuring technique [2] showed that the electrical potential difference records give direct information about the physiological activity of standing trees [6]. The electrical potential differences of natural origin are influenced by many environmental factors, first of all by microclimatological conditions. As a first approximation the trunk itself is to be considered as a cylindrical structure. Consequently its electrical resistivity distribution is assumed to have a cylindrical structure, i.e. it is expected to be a two-dimensional model. The experienced inhomogeneities shown by these natural potential differences oriented us to investigate the internal structure of the trunk in another way, too. Namely, instead of recording these natural potential differences, potential differences, due to current electrodes on the surface of the trunk of living trees, are measured. In the geophysical practice there exist several techniques, which can be applied to this problem. In the poster presentation an overview about some classical geo-electric techniques (Schlumberger soundings, Wenner configurations, etc.) are shown. Some of these techniques are useful in determination the centre of the bulk resistivity within the trunk of a standing tree. The results of such an inhomogeneity mapping (that is comparing the results measured on the surface of the trunk at different site but at the same height) can be directly transformed into resistivity dimensions [7]. This geoelectric method would offer an in vivo non-invasive method. It cannot give such detailed pictures as the high-frequency tomograph methods, but it may give important auxiliary information to the application of such other techniques.
References: [1] Morat P., Le Mouel J-L., and Granier A.: Electric potential on a tree. A measurement of the sap flow?, Compte Rendu Acad. Sci. Paris, Sciences de la Vie/Life Sciences 317 (1994) 98-101. [2] Granier A.: Mesure du flux de sčve brute dans le tronc du Douglas par une nouvelle méthode thermique, Ann. Sci. For. 44 (1987) 1-14. [3] Koppán A.: Time variation of electrical potential differences in Fagus Sylvatica. Diploma work, Sopron University, 1996 [4] Koppán A., Szarka L., Wesztergom V.: Temporal variation of electrical signal recorded in a standing tree, Acta Geod. Geoph. Hung. 34 (1999) 169-180 [5] Koppán A., Szarka L., Wesztergom V.: Temporal Annual fluctuation in amplitudes of daily variations of electrical signals measured in the trunk of a standing tree (2000), paper submitted to Compte Rendu Acad. Sci. Paris, Sciences de la Vie/Life Sciences. [6] Koppán A., Fenyvesi A., Szarka L., Wesztergom V.: Comparison of electric potential difference recordings and direct sap flow intensity measurements in the trunk of a standing tree. Paper submitted as poster to the Spring Meeting of the American Geophysical Union (2000) [7] Weidelt, P., Weller A.: Computation of geoelectrical configuration factors for cylindrical core samples. Scientific drilling, 6 (1997), 27-34.
Publication Source: Proceedings of the 12th International Symposium on Nondestructive Testing of Wood University of Western Hungary, Sopron, 13-15 September 2000, ISBN 963 7180 88 5 Publisher: University of Western Hungary, H 9400 Sopron, P.O.Box 132, FAX: +36 99 311 103
