Mechanical properties of branch and stem wood for two Mediterranean cultivars of olive tree

Abstract

There is currently a strong interest in wood and the demand for this material is expected to grow significantly worldwide. Consequently, market demand for wood from fruit orchards is growing as an additional source of supply. For these reasons, several studies were conducted to evaluate the properties of wood derived by orchard pruning or dismantling. Despite the abundance of raw materials from pruning, the mechanical properties of olive wood have not been studied completely by the scientific community, so the woody material obtained is usually considered waste or firewood. In fact, there is still a lack of knowledge about olive wood characteristics and considering the valuable role of olive species in the Mediterranean area, the current study aimed to determine and compare the physical and mechanical properties of branches and stem wood of two olive tree cultivars, “Sinopolese” and “Ottobratica”, to provide information on this wood species. These two olive cultivars are commonly cultivated in the Calabria region (Southern Italy) for the extraction of oil from drupes, but large masses of wood are derived from their pruning. For the choice of parts, the stem was considered to become a branch when, above each branch intersection, it changed in diameter and direction of growth. The branches with a diameter lower than 20 cm were excluded. The tests conducted for this purpose were: Roughness profile; Impact wave; Vibrational analysis; Static modulus of elasticity; Bending strength; Abrasion resistance; Static hardness; Footprints; Compression strength; Screw withdrawal resistance parallel to grain; Screw withdrawal resistance perpendicular to grain. A MANOVA analysis was conducted between the Cultivar-Tree part and the physical and mechanical properties. The results showed some differences between the two cultivars principally related to mechanical properties such as moduli of elasticity and rupture, footprint, compression strength, and screw withdrawal resistances, where in general, the “Sinopolese” cultivar showed higher values than the “Ottobratica”. Between the tree parts (stem and branches) within the same cultivars, branches demonstrated higher results in the majority of the tests, but highlighting statistical differences only in terms of static modulus of elasticity, bending strength, static hardness and screw withdrawal resistances depending on the cultivar. This result suggests that the branch wood, with its characteristics, could be valorized in the commercial utilization representing a valid opportunity for the local rural economy, even considering the conspicuous amount of wood obtained from olive pruning activity. Expanding knowledge about olive wood in terms of physical and mechanical characteristics could increase its use in multiple sectors and ensure a more aware use of the application of the wood resources by supporting the decision on its best end use.