Elsevier

Biosystems Engineering

Volume 112, Issue 4, August 2012, Pages 352-358
Biosystems Engineering

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

https://doi.org/10.1016/j.biosystemseng.2012.05.007Get rights and content

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.

Highlights

► Mechanical harvesting of Pinus pinea L. responds to trunk vibration parameters. ► High cone efficiency and low tree damage with trunk frequency range 16–19 Hz. ► Two short time vibration repetitions are effective for harvest. ► Avoid vibration time up to 4 s and harvest after shoot elongation.

Introduction

The stone pine (Pinus pinea L.) is a species adapted to dry sandy or rocky soils in Mediterranean temperate forests. This pine tree produces edible kernels that are highly valued for their culinary uses. Around 460,000 ha of stone pine are cultivated in Spain, representing two-thirds of the worldwide crop, with an average production between 2006 and 2008 of 10,500 Mg at a price between 1500–2500€ Mg−1 (MARM, 2008). This species is an additional source of income in many regions and towns in the Mediterranean basin. In fact, the income derived from the cones in productive plantations is much greater than that associated with the production of lumber or firewood.

The cones require three years to reach maturity; therefore, cones from three consecutive crops coincide on the tree each spring (Mutke, Gordo, & Gil, 2005). The harvesting method applied to cones requires a system capable of discriminating between ripe and unripe cones and other tree organs, detaching only the mature cones. Traditionally, the selective harvesting of cones was performed manually; the workers climbed the tree and, aided by tools, selected the mature cones. This involves a high risk for the worker and elevated harvesting cost. In Andalusia, the region with the greatest production in Spain, the number of work-related accidents occurring during the cone harvest is the primary factor for the local government's examination and regulation of harvesting systems.

The mechanical harvesting of cones is conducted using trunk shakers. This practice is common in countries such as Italy. Since the 1980s, the economic advantages of mechanical harvesting as opposed to manual harvesting have been made evident. However, possible damage to the tree and tree growth reduction must be considered (Bonari, Bagliacca, Ciomei, & Senesi, 1980; Montero-González, Candela-Plaza, & Rodríguez-Navarro, 2004). In some cases, the mechanical harvesting of stone pines reveals no damage to the trees (Bonamini & Cherubini, 1988; McLemore & Chappell, 1973) or that the damage due to the breaking of shoots may actually aid the tree in increasing in diameter any height that is lost (Peruzzi, Mazzoncini, Ciomei, & Senesi, 1989). However, other authors warn about the increase in damage which could occur when the vibration is produced under rainy (Bonari et al., 1980), and freezing conditions (Castellani, 1973), when the trees are in an important vegetative state (Martinez-Zurimendi et al., 2009) or when the vibration times are lengthened (Miles, Mehlschau, & Moini, 1981). Recently, Portugal and Spain have introduced mechanical harvesting using trunk shakers, primarily from the mechanical harvesting of olive trees. The use of these machines causes damage as they remove immature cones and shoots (Barriguinha et al., 2005; Martinez-Zurimendi et al., 2009; Pinheiro et al., 2003), as well as cause rutting and soil compaction as a result of machine traffic (Eliasson, 2005).

The response of each crop to forced vibration is of great interest in order to improve the efficiency and quality of mechanical harvesting. Vibration frequency is one of the most important adjustments made to harvest agricultural species. In the vineyards, changes in frequency are attributable to harvest losses and the quality of the harvested fruit (Pezzi & Caprara, 2009). Frequency range for the harvest of different agricultural species varies greatly from species to species. Studies performed place the most efficient frequency values near 15 Hz for citrus and apricot trees (Erdoğan, Güner, Dursun, & Gezer, 2003; Torregrosa, Ortí, Martín, Gil, & Ortiz, 2009), between 15 and 20 Hz for boxthorn berries (So, 2003), at values of 20 Hz for pistachios (Polat et al., 2007) and at a range between 28 and 30 Hz for the harvest of intensive olive tree orchards (Castro-García, Blanco-Roldán, Gil-Ribes, & Agüera-Vega, 2008).

The response of the tree and its different organs to trunk vibration, as well as the power required during the process, depends on the dynamic characteristics of the tree (Horvath & Sitkei, 2001). In the case of the stone pine, the resonance frequency of the peduncle of the mature cone is found within a frequency range of 18.0 ± 5.3 Hz. The morphological changes of the mature cone and increase in mass and size of its fruit-stalk system produce a differentiated response of the mature cone, facilitating its detachment as it amplifies the acceleration values transmitted by the machine through the branches (Castro-García, Blanco-Roldán, & Gil-Ribes, 2011).

The management of trunk shakers by different operators is another important parameter for a good harvest. It is common for the machine operator to change the modus operandi of the shaker during the harvesting season, with the objective of achieving greater harvest cone efficiencies (Bonari et al., 1980). These practices include prolongation of the vibration time and the use of various vibrations on each tree (Blanco-Roldan, Gil-Ribes, Kouraba, & Castro-García, 2009). The use of these practices and the adjustment of the shaker affect harvest efficiency and the potential damage caused to the tree during mechanical harvesting.

The objective of the study was to analyse the detachment of cones and shoots with the use of a trunk shaker using different variations of frequency, duration and vibration repetitions. The evaluation of mechanical harvesting was performed to maximize the number of mature cones harvested while limiting any potential damage caused to the tree. The results obtained are important for the adaptation of trunk shakers used on agricultural species to the needs of stone pine and the implementation of good harvesting practices and improvement of sustainable production of non-wood forest products.

Section snippets

Material and methods

The mechanical harvesting tests were performed with stone pine during the 2010 and 2011 seasons in two forests located in southern Spain. In both forests, the climate was Mediterranean, characterised by long, dry and hot summers, with more humidity in the autumn and spring. The main characteristics of the plantations are summarised in Table 1. The mechanically harvested trees were selected among the trees that had the greatest cone production and ages over 50 years.

The field tests employed a

Results and discussion

The removal of mature cones from stone pines proved to be feasible using trunk shakers. However, the possible damage caused to the tree, primarily from the falling of shoots, immature cones and the stripping of bark from the trunk, requires the establishment of limitations for the implementation of good harvesting practices and the improvement of the sustainable production of non-wood forest products.

Three frequency ranges were established according to the three positions selected with the flow

Conclusions

Trunk shaker is an adequate harvesting system for the harvesting of stone pine capable of limiting the damage caused to the tree by adjusting the machine and the work of the machine operator. High harvesting efficiencies of mature cones (85.7%) can be reached with vibration frequencies between 16.1 and 18.9 Hz, and acceleration values at the trunk of 51.2–78.4 m s−2. The detachment of mature cones during the first seconds of the vibration justifies the use of vibrations with durations of less

Acknowledgements

The authors acknowledge the financial support from “Agencia de Medio Ambiente y Agua” and SEFOSA financed by “Corporación Tecnológica de Andalucía (CTA)” and “Agencia IDEA” of the Regional Government of Andalusia, Spain. The authors also acknowledge the financial support of the Regional Government of Andalusia (2008-00048; project PI45120) for the research methodology and instrumentation used.

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