Frequency response of Pinus Pinea L. for selective cone harvesting by vibration

Abstract

The stone pine (Pinus pinea L.) is exploited for wood production and its edible kernels. Cones take 3 years to mature, while other newer cones are growing on the tree. Currently, mechanical cone harvesting by tree vibration drives the profitability and development of this crop in forest ecosystems. However, the adaptation of vibration parameters is necessary to avoid damage to the tree and for the implementation of good harvesting practices. Direct measurements of acceleration transmissibility along fruit-bearing branches under controlled laboratory conditions showed that vibrations in the frequency range of 18.0 ± 5.3 Hz were capable of producing resonance phenomena in mature cones. Morphological changes produced in the mature cones, especially in the stalk and total weight, amplified the acceleration transmissibility, providing more favourable conditions for fruit detachment. Field tests with stone pines and a trunk shaker confirmed the potential of selective mechanical harvesting, which is conditional on the vibration parameters applied. The frequency range of the resonance of the mature cone proved to be suitable for vibration of the tree at its trunk. The quality and efficiency of the mechanical harvesting were determined to be inversely related parameters during harvesting by vibration. Trunk vibration at a frequency of 18 Hz and approximate acceleration of 65 m/s2 achieved a high harvest quality, with limited detachment of shoots and unripe cones, and a harvesting efficiency near 85%.