Western Australian sandalwood, Santalum spicatum, is widespread in the semi-arid and arid regions of Western Australia, and there is some morphological variation suggestive of two ecotypes. The level and structuring of genetic diversity within the species was investigated using anonymous nuclear RFLP loci. Santalum spicatum showed moderate levels of genetic diversity compared to other Australian tree species. The northern populations in the arid region showed greater levels of diversity and less population differentiation than the southern populations in the semi-arid region due to differences in the distribution of rare alleles. Equilibrium between drift and gene flow in the northern populations indicated that they have been established for a long period of time with stable conditions conducive to gene flow. In contrast, the southern populations showed a relationship between drift and gene flow indicative of a pattern of fragmentation and isolation where drift has greater effect than gene flow. The different patterns of diversity suggest that the ecotypes in the two regions have been subject to differences in the relative influences of drift and gene flow during their evolutionary history.

Western Australian sandalwood (Santalum spicatum) is widespread throughout Western Australia across the semiarid and arid regions. The diversity and phylogeographic patterns within the chloroplast genome of S. spicatum were investigated using restriction fragment length polymorphism analysis of 23 populations. The chloroplast diversity was structured into two main clades that were geographically separated, one centred in the southern (semiarid region) and the other in the northern (arid) region. Fragmentation due to climatic instability was identified as the most likely influence on the differentiation of the lineages. The lineage in the arid region showed a greater level of differentiation than that in the southern region, suggesting a higher level of gene flow or a more recent range expansion of sandalwood in the southern region. The phylogeographic pattern in the chloroplast genome is congruent with that detected in the nuclear genome, which identified different genetic influences between the regions and also suggested a more recent expansion of sandalwood in the southern region.

Initially, the size-class structure of 1067 natural sandalwood (Santalum spicatum) trees and seedlings, growing in populations at three semi-arid sites (Burnerbinmah, Ninghan and Goongarrie) in Western Australia, was measured during 1996–97. These same populations, and any new sandalwood seedlings and small trees that had established after 1996–97, were measured again after 17 years (2013). Size-class structure was assessed by measuring over-bark stem diameter at 150 mm above the ground. Populations of sandalwood trees at the Burnerbinmah and Ninghan sites failed to regenerate and, after 17 years, they contained only 0–3% small trees and 0–2% seedlings. Their overall population size declined by 21–24% and, combined with recruitment failure, these natural stands of sandalwood may largely disappear within 50–60 years. At the Goongarrie site, the proportion of large trees within the natural population increased from 58% to 82%. The proportion of small trees was constant at 13–16%, while seedlings declined from 29% to 2%. The population reduced by 35%, mainly due to high seedling mortality. Although the population was in decline, there appeared to be enough small trees and seedlings to maintain the population longer than at both the Burnerbinmah and Ninghan sites. In a second study, 16 640 sandalwood seeds were sown at the same three sites during 1996–97, and then assessed for germination, survival, growth and fruit production over 17 years. Sandalwood germination and growth were compared between locations, fencing treatments and land systems. Seed enrichment was successful at each site with 27–45% germination and 6–20% survival (from germinated seeds) after 17 years. The overall seedling survival rates (from total seeds sown) ranged from 2.1% to 5.2%. Mean stem diameter of seedlings was significantly larger at Goongarrie (37 mm) than at both Burnerbinmah and Ninghan (20–22 mm) sites. Grazing significantly affected the performance of sandalwood seedlings at an age of 17 years at the Ninghan site. At this site, seedling survival (from germinated seeds) was 16% in the fenced plots compared with only 6% in the unfenced plots. Mean stem diameter in the fenced plots (24 mm) was also significantly greater than in the unfenced plots (11 mm). Land systems did not affect survival of sandalwood seedlings at the Burnerbinmah site but had a significant impact at the Goongarrie site after 17 years. Seedling survival was significantly greater on the hills and ridges than those growing on the plains with granite and red sand plains. Seed-enrichment programs are recommended to improve long-term regeneration and sustainability of sandalwood trees.

Thirty-two Indian sandalwood (Santa/um album) trees aged 16 y, growing near Kununurra (Western Australia), were harvested, de-barked and weighed to determine their commercial wood (heartwood and sapwood) weights. Within each tree, heartwood area, percentage and weight were measured in stem cross-sections at five different heights (0, 0.50, 1.00, 2.00 and 3.00 m above the ground) in the main stem, and used to estimate total heartwood volume and weight. Heartwood oil concentration and ex-and fo.santalol concentrations were also measured at the same heights in each tree.At age 16 y, the 32 S. album trees had mean estimated air-dry weights (at -12% moisture content) of 5.8 kg heartwood tree-1 and43.7 kg sapwood tree-1 • The mean air-dry wood densities were 940 kg m-3 for the heartwood and 840 kg m-3 for the sapwood. Estimated heartwood weight was variable between trees, with the three largest trees each containing 24--30 kg heartwood, while nine other trees each had 0-1 kg heartwood. The S. album plantation in this study contained about 260 trees ha-1 , and its predicted yields (air-dry weight) at age 16 y were 1.5 t heartwood ha-1 and 11.4 t sapwood ha-1 • Within each tree, the mean oil concentration (w/w air dry) ranged from 6.2% (at 0 m) to 2.9% (at 3.00 m). Overall, the mean oil concentration within the heartwood was 5 .0%, giving estimated yields of 0.28 kg oil tree-1 and 73 kg oil ha-1 (based on 260 trees ha-1 ). The mean ex-santalol concentration ( 44--50%) and P-santalol concentration ( 18-20%) at the five different tree heights met the current ISO standard for S. album oil.In the 16-y-old S. album trees, over-bark stem diameter at 300 mm above the ground correlated well to both total air-dry weight of wood (heartwood and sapwood) per tree (r 2 = 0.88) and heartwood air-dry weight per tree (r 2 = 0.87). This indicated that large-diameter trees had markedly higher heartwood weights.

Sixty-four sandalwood (Santa/urn spicatum) trees aged 8-26 y were harvested from five separate plantations during 2007 to determine wood yields and quality (percentage heartwood; oil and a-santalol concentrations) at different ages. Each plantation was located in the 400-600 mm mean annual rainfall zone in south-western Western Australia. The whole trees, including the roots, were extracted from the ground, de-barked and the wood divided into five separate commercial wood grades: butt, roots, 1st grade, 2nd grade and 3rd grade.Mean percentage heartwood and oil concentration in the wood increased significantly with sandalwood age. However, mean a-santalol concentration in the oil was less age-related, but was generally high in the trees aged 26 y. Both oil and a-santalol concentrations were relatively high in the butt, roots and l st-grade wood from trees aged 26 y, and only in the butt of trees aged 14 y. Wood of all grades from trees aged 8-11 y was of low value. These results indicate that to obtain a large proportion of high-grade wood from sandalwood plantations the stand age may have to be at least 25 y.A power relationship equation was developed to predict the total commercial weight of wood within a sandalwood tree knowing stem diameter over bark at 150 mm above the ground. Within each tree, the greatest amount (33-46% of the total weight) of commercial wood was classed as 1st grade, and each ofthe other four grades contained 10-23% of the total.