Vibrational and operational parameters in mechanical cone harvesting of stone pine (Pinus pinea L.)

Mechanical harvesting of the stone pine (Pinus pinea L.) with trunk shakers is replacing manual harvesting. The machines used are generally involved in the mechanical harvesting of agricultural species; their adjustments and use are not adapted to the needs of forest species. The objective of this study was to analyse the vibration process and maximise the number of mature cones harvested whilst limiting any potential damage caused to the tree. Tests were performed in two stone pine plantations located in southern Spain on two harvest dates. The vibration parameters, the harvest efficiency of mature cones and the damage caused to the tree by the loss of shoots, immature cones and damage to the bark were analysed. Adjusting the trunk shaker in a frequency range of 16.1–18.9 Hz and the effective acceleration values at the trunk in the range 51.2–78.4 m s−2 removed an average value of 85.7% of the mature cones from the tree. With these parameters, the average damage caused to the tree was less than two non-harvestable organs per tree. The harvest date was a fundamental parameter in limiting the damage caused to the tree and bark, avoiding vibration after the start of development of new shoots. Vibration periods of more than 4 s were not effective in increasing the number of mature cones removed. Tree vibrations with two short-duration vibrations were effective in increasing the amount of mature cones removed without increasing the damage caused to the tree.