Annual fluctuation in amplitudes of daily variations of electrical signalsmeasured in the trunk of a standing tree

Electrical potential differences between electrodes inserted in eight selec ted sites of the trunk of a Turkey oak (Quercus cerris) and the ground have been recorded continuously since November 1997. The mean amplitudes of dai ly electric variations were determined for time intervals when the meteorol ogical and atmospheric electricity conditions were undisturbed. It was foun d that the mean daily amplitudes show a characteristic annual fluctuation. Both in 1998 and in 1999 two peaks were observed: the first maximum appears suddenly about the end of March, and the second one was seen in late lune, July. Between November and March the mean amplitudes were smaller by about one order of magnitude. (C) 2000 Academie des sciences/Editions scientifiq ues et medicales Elsevier SAS.