Assessment of aerial and underground vibration transmission in mechanically trunk shaken olive trees

The present study analyses the transmission of vibrations generated from a multidirectional trunk shaker to olive tree structure considering both the aerial zone (trunk and branches) and the underground zone (the coarse root). The vibration characterization was conducted by measuring acceleration on several points of the tree during harvesting operations. The influence of two different heights of shaker head clamping was analysed. In addition, a dynamic probing was performed in order to evaluate soil compaction. The results showed that the vibration performed by the trunk shaker head, corresponding to an acceleration resultant of approximately 77 ms^–2 with a dominant vibration frequency of 18 Hz, increased up to 106% in branches and decreased up to 90% in trunks. At root level, where the analysis was carried out at 1/3 and 2/3 of the coarse root length, the acceleration values diminished significantly to 17 ms^–2 and 12 ms^–2, respectively. Soil dynamic resistance was lower (36 kg cm^–2) near the trees than between the trees (53 kg cm^–2). The vibration transmission to the aerial and the underground parts diversely influences the dynamic behaviour of the olive tree, considering an operational frequency of a commercial trunk shaker. The assessment of vibration transmission to the aerial part could contribute to improve fruit detachment and reduce branch breaking and leaf detachment. While vibration transmission to the underground part rises new challenges considering soil compaction in olive groves.