Heartwood rot (a fungal disease) has the potential to significantly reduce sandalwood oil production from Santalum album.
As new sandalwood plantations are established in Australia, with the oil as the major product, it is important to know the consequences of routine form-pruning in tropical areas.
Sandalwood (S. album) is an obligate wood hemiparasite that produces a highly valued essential oil from its heartwood. Within the Santalum genus, several species produce similar sandalwood oil components, but the proportions differ. S. album is the most sought after because it produces the highest levels of the essential santalols and easily meets the ISO standard for the valuable high-end perfume market.
The natural S. album stands of Timor-Leste and India are insufficient to meet world demand for sandalwood oil, so plantations are being established across the natural sandalwood range of the Pacific Rim and northern Australia. Currently, northern Australia is managing more than 13,000ha of S. album plantations.
The oil of sandalwood is a complex mixture of sesquiterpenes, which the tree naturally produces in its heartwood to protect against pests and disease.
Pruning trees to encourage a single stem is a standard industry practice and aims to direct the vigour of the tree into increasing the size of the valuable lower bole.
Unfortunately, pruning can also allow fungal pathogens to get in and damage the tree’s growth, subsequently reducing heartwood development, oil production and economic value.
With no consensus on when or how to prune, a West Australian research team, led by Murdoch University’s Dr Treena Burgess, examined pruning wound responses in one- and five-year-old trees at the end of dry and wet seasons.
They found that age was a significant factor, with younger trees suffering less decay after pruning, due to the smaller wounds created, fewer fungal species being present and a better occlusion response and rate.
On the other hand, the season during which trees were pruned did not affect the response to wounding, decay rating, or the number of fungal species present.
Source:
Burgess, T.I., Howard, K., Steel, E., & Barbour, E.L. (2018). To prune or not to prune; pruning induced decay in tropical sandalwood. Forest Ecology and Management, 430, 204–218.
Image (courtesy of Dr Burgess): sections of sandalwood (S. album) split at the pruning site showing decay ratings (from 0, no rot evident, to soft rot in 6).
