Opportunities for the smallholder sandalwood industry in ... - ACIAR

Productivity of planted sandalwood
The value of a sandalwood tree is largely determined
by the weight of its heartwood and the concentration
and composition of the oil contained within it (Doran
et al. 2005). Determining the rate of heartwood development
in a sandalwood tree is important, since it
will largely determine the length of its commercial
rotation. The weight of the heartwood is invariably
limited by, or dependent on, the size of the tree. Very
little information has been published regarding the
rate of growth in S. austrocaledonicum.
Growth rates
Growth rates were measured in 1,685 sandalwood
trees planted across five islands of Vanuatu (Santo,
Malekula, Efate, Erromango and Tanna). Four broad
management regimes were identified:
• commercial—intensively managed with fertiliser
added
• enrichment—planted within an existing natural
namariu (Acacia spirorbis) forest
• new garden—planted in a newly cleared garden at
the same time as all other crops
• old garden—growing in a garden area no longer
used as such.
Given the prevalence of both enrichment and new
garden plantings, the number of trees measured in
these two categories constituted 84% of the trees
sampled (Figure 11). No statistical differences in the
mean annual basal increment were found between
these two planting types, with a basal diameter
growth rate of 1.08 cm per year. Sandalwood grown
under commercial conditions was found to have significantly
greater growth rates than all other management
regimes, largely due to the attention to host-tree
planting and fertiliser additions. Trees planted in old
garden areas were found to have significantly slower
growth rates than all other management regimes.
Although 93% of the data were collected from trees
aged 10 years and under, these differences in early
growth rates are likely to persist in later years. In the
commercial category, only two growers were sampled,
one in each of Efate and Santo. The maximum age of
these trees was 3 years (as these were the only ones
available) and, given the higher relative growth rates
of S. austrocaledonicum in its earlier years (Thomson
2006), this sampling regime is likely to elevate the
growth rate estimates of the commercial plantings
relative to the enrichment and new garden plantings.
Although the sample size of the old garden category
was also small, the age classes represented ranged
from 3 to 13 years, and the data collected for this
category are likely to reflect the growth rates relative
to the enrichment and new garden plantings.
Heartwood development
As for growth rates, there have been few studies on
the rate of heartwood development of S. austrocaledonicum,
and estimates based on S. album (Rai
1990; Haffner 1993; Radomiljac et al. 1998) may
not be applicable to sandalwood in Vanuatu. Many
sandalwood resource owners, and more particularly
agents and buyers in Vanuatu, have experience in
determining the approximate weight of heartwood
in a standing tree of a known age. This study drew
on this experience and used an agent of one of the
existing sandalwood licence holders with more than
10 years experience to determine the weight of
heartwood across 109 trees of a known age growing
on the main production islands of Tanna and
Erromango. Although the heartwood weights are
based on estimates, every effort was taken to verify
the figures with experienced industry participants.
Therefore, we are confident that these data provide
a reasonable reflection of heartwood development
in S. austrocaledonicum growing under appropriate
conditions in Vanuatu. Further research would
improve the accuracy of these data.
The regression between tree age and heartwood
weight indicates that heartwood development may
begin at 7.5 years, and increase at a rate of approximately
2.5 kg per year thereafter (Figure 12). While
the R 2 value of 0.71 indicates that age explains much
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