Variations in composition and yield of leaf oils from alley-farmed oil mallees (Eucalyptus spp.) at a range of contrasting sites in the Western Australian wheatbelt

Variations in the amount and composition of leaf oil of alley-farmed 'oil mallees' were examined at wide-ranging sites across the Western Australian wheatbelt. Of four particularly promising species studied at six locations in respect of oil composition, 1,8-cineole comprised 65-92% of the total oil. Up to 32 constituent oils were present in proportional amounts ranging from 0.01 to 13%. A further 26 trace components were recorded in certain species. Relative abundances of cineole, limonene, alpha-terpineol and terpinen-4-ol varied significantly between sites for all four species, with evidence of reduced levels of cineole being compensated for by increases in the latter three compounds. Foliar yields of cineole of all nine taxa were assessed for 2.5- or 3-year-old saplings cut respectively in summer or winter, and for corresponding coppice biomass produced over the following 12 months from the same trees. Average leaf cineole yields for the five best performing taxa varied widely between species and sites, with sapling harvests producing 12-130 (mean 49) kg cineole per kilometre of twin-row hedge compared to 1-68 (mean 23) kg km(-1) for subsequent coppice harvests. While genotype was primarily important in determining leaf cineole concentration, modifying effects of season and leaf age balance were evident for both sapling and coppice canopies. Cineole concentrations were generally greatest in early summer when particularly high proportions of recently matured leaves were present. Of the. nine taxa studied, two provenances of Eucalyptus vegrandis were discounted on grounds of poor growth and low cineole concentrations, another (E. kochii subsp. kochii) rated unsuitable due to inbreeding depression in available seed sources, and a further species (E. angustissima) deemed useful only at winter-wet, saline, sandy sites. The remaining taxa (E. kochii subsp. plenissima, E. horistes, E. polybractea, E. loxophleba subsp. lissophloia and E. gratiae) showed general ability to yield well at favourable sites. With such large ranges in cineole yields between taxa and sites, the study advocated that successful commercial culture of oil mallees would require careful selection of species for location of planting, and adoption of management practices conducive to maximum possible biomass and build up of foliar oils in coppice growth at harvest. (C) 2000 Elsevier Science B.V. All rights reserved.