Natural diversity of Santalum spicatum host species in south-coast river systems and their incorporation into profitable and biodiverse revegetation

Abstract

The commercially valuable root hemiparasite Santalum spicatum (R.Br.) A.DC. (sandalwood) once grew throughout the medium- to low-rainfall areas of the south-western agricultural region of Australia; however, this resource has been exhausted by over-exploitation and clearing for agriculture. There has been growing interest from the farming community and other investors in the development of a plantation Santalum spicatum industry in southern Western Australia. This study investigated the distribution of remnant S. spicatum within the Pallinup River catchment and assessed the risk of S. spicatum population decline due to salinity. The natural range of host species at different sites (river catchments) across the south coast was also investigated. Remnant populations of S. spicatum within and adjacent to the Pallinup River catchment were small (1–70 trees) and highly fragmented. The risk of further population decline due to salinity was concluded to be small because remnant trees were generally growing in well drained, sandy soils that were elevated above (median 9 m) their immediate drainage line. Across the seven river catchments surveyed, S. spicatum occurred in a range of vegetation associations and parasitised numerous species (68) from a wide range of genera and families. The suite of species exploited varied within and between catchments. Thirty species, including most monocots and Myrtaceae, were not successfully parasitised. Remnant S. spicatum always occurred on well drained soil types that supported open-woodland or mallee–heath communities. Sandalwood plantations, supported by numerous individuals of a range of host species (10–40 species), were shown to be productive in terms of sandalwood growth. The scale of the developing sandalwood plantation industry is likely to be small and unlikely to cover large areas of catchments. Thus, this industry alone is unlikely to address the salinity crisis through broadscale recharge management. However, additional to on-site recharge reduction, biodiverse host plantations may improve the prospects for biodiversity and rivers in salinising landscapes through the protection and enhancement of natural biodiversity, creation of new habitat, conservation of plant species and by providing a commercial incentive to protect biodiversity.