Stimulation of Western Australian sandalwood (Santalum spicatum) oil production using multiple treatments

Abstract

Sandalwood is an important international commodity recognised for its aromatic oil, which is a key ingredient in many fragrances and cosmetics. Western Australian (WA) sandalwood (Santalum spicatum) is identified as a cheaper, lowerquality alternative to the superior Indian sandalwood (Santalum album). Natural stocks of both S. album and S. spicatum have declined due to historical mismanagement. Subsequently, WA sandalwood has been established in plantations in Western Australia to attempt to meet the demands of the sandalwood industry. Plantation WA sandalwood is promoted as agroforestry, promising economic and environmental benefits. While these benefits are attractive, WA sandalwood has an estimated 25-year rotation. This research aimed to determine the effect of physical and chemical treatments on oil production and heartwood formation in WA sandalwood, aiming to increase oil production, thus reducing the time between establishment and harvesting. The study was conducted over three plantations in the Wheatbelt region of Western Australia: ‘Sandawindy’, ‘Kylie Reserve’ and ‘Brookton’. At each site, four treatments were applied: a dowel soaked with the plant hormone methyl salicylate (MeSA) and inserted into the tree (Treated Dowel), a dowel with noMeSA inserted into the tree (BlankDowel), a drill hole left empty (Empty Drill), and a section of bark removed from the tree (Bark Removed). A group of treeswas left as a control comparison. The Blank Dowel and Empty Drill treatments were established to determine if any significant increases of sandalwood oil in the Treated Dowel treatment were a result of the MeSA, the dowel or drilling into the tree. The Bark Removed treatment was used to mimic drysidedness, a naturally occurring condition common in the rangelands of Western Australia as a result of sun scald. Sandalwood trees were measured and treated in November 2016. Three hundred trees were treated at each plantation, allowing for 60 trees of each treatment at each plantation. Twenty trees for every treatment and control group at each plantation were harvested in November 2017, and all trees were remeasured. Of the approximately 300 trees harvested, 150 were cored using a 12 mm auger drill. These core samples were analysed for oil yield and composition. Total oil was measured and analysed, as well as oil constituents αsantalol, β-santalol, farnesol, nuciferol and β-bisabalol oil compositions (percentage) and yields (%w/w). All harvested trees were cut into eight 25 mm discs, and the percentage of heartwood area at each height was measured. All data were statistically analysed using a univariate general linear model. No treatment consistently increased total oil, or oil component yields, qualities or heartwood area percentages. The presence of MeSA did not have a significant effect on oil production; rather, the physical wounding of the tree had the overall greatest effect. Kylie Reserve showed low oil yield and low heartwood area percentages compared to the other plantations, while simultaneously showing the highest oil yields. This research indicates that a longer period between treatment and harvesting could influence oil production. Further, research extending this study should be conducted to gain more insight into the effect of the treatments on oil production.