annual report 2011 - Forestry Tasmania

Managing leaf beetles: how well are we doing? Can we improve?
Dr Tim Wardlaw
Karl Wotherspoon
Leonie Jordan
Tim.Wardlaw@forestrytas.com.au
Karl.Wotherspoon@forestrytas.com.au
Leonie.Jordan@forestrytas.com.au
For the past two years, the Forestry Tasmania Forest Health
Surveillance system has been used to measure how well
our leaf beetle management protects plantations from
defoliation. Linking records from the Forest Operations
Database of leaf beetle population monitoring and control
(spray) events, to assessments of end-of-season defoliation,
allowed calculation of how much defoliation was prevented.
The costs of management were then compared to the
value of growth losses avoided. We found that spending
$540,000 annually on leaf beetle management prevented
growth losses worth $955,000 – that is, each dollar spent on
management saved $1.76 from the value of the plantation
estate.
Leaf beetle management was most effective, and provided
the greatest financial benefit, in plantations 5-6 years old.
Financial benefit declined in older plantations because
monitoring was less able to detect leaf beetle populations,
and also because some defoliation was suffered by older
plantations that were not monitored for leaf beetles: leaf
beetle management has traditionally been done in younger
plantations, and it is only recently that management
has been extended into older plantations. If losses from
no management or ineffective management in older
plantations could be eliminated, the financial benefit of the
program would nearly double.
In a separate study, Sophie Edgar from the University of
Tasmania used our operational leaf beetle population
monitoring records to examine whether variation in leaf
beetle populations could be predicted by site, climate
or landscape attributes. Two risk factors – altitude, and
proximity to Poa grasslands – were the most useful
predictors of leaf beetle populations: the likelihood
of leaf beetle populations being above-threshold was
2-6 times higher in high-risk plantations than in lowrisk
plantations. Using these factors to segregate the
plantation estate into areas of low, medium and high risk
of supporting above-threshold leaf beetle populations
could thus provide substantial efficiency gains in leaf
beetle management. Shifting from age-based targeting
of plantations to risk-based targeting is predicted to result
in 35% more above-threshold leaf beetle populations
being detected for the same monitoring effort.
Forestry Tasmania will thus be adopting risk-based
targeting of plantations for managing leaf beetles in the
2011-12 season. Additionally, we are refining the way we
monitor leaf beetle populations to better suit the larger
trees found in older plantations.
This work has highlighted the value of information
describing our plantation operations that has been
captured in the Forest Operations Database. Combining
this information with assessments of damage made by
health surveillance provides a powerful tool to evaluate the
effectiveness of our management.
Eucalyptus leaf beetle Paropsisterna bimaculata
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