  In this paper, we revisit old electrical measurements conducted on a poplar
tree in 2003 (Gibert et al. 2006), which showed the presence of a diurnal
electrical signal, attributed to an electrokinetic phenomenon correlated with
sap flow, even in winter. We reanalyze these data using the singular spectrum
analysis method and demonstrate that the electrical signal measured at various
locations (roots, trunk, and branches) on the poplar tree can be decomposed to
over 80\% into a sum of 7 pseudo-periods, all linked to luni-solar tides. The
precision of the extracted periods exceeds that of models. To validate these
old measurements, we have reproduced the 2003 protocol since 2018 at the Jardin
des Plantes in Paris, on 3 oak trees and 3 hornbeams. The electrical signals
today exhibit the same characteristics as those of 2003. Tidal forces could be
a driving force of sap flow in trees.
