A version of the forest growth model CABALA is being developed
that that will allow users to examine the impact of defoliation on
plantation productivity. Users can stipulate the pattern, severity,
timing and frequency of defoliation, as well as foliage
discoloration (e.g. due to pathogen attack) and any silvicultural
interventions.
The model was tested using a detailed dataset collected for pre-
and post-canopy-closure Eucalyptus globulus grown at the
Pittwater plantation near Hobart. The Pittwater work was undertaken
by Libby Pinkard, CRC postdocs Alieta Eyles and Karen Barry, and
PhD student Audrey Quentin, and focused on the effects of water and
nutrient stress on responses to artificial defoliation, in terms of
gas exchange (foliar and stem) and patterns of resource allocation
(biomass, nitrogen, carbohydrates).
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Figure 1. Observed (symbol) and predicted (line)
entire stem volume of E. globulus growing at Mawbanna in
north-west Tasmania following 50% defoliation by autumn gum moth at
age two years
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The model has been validated against a number of experimental
datasets involving insects, pathogens or artificial defoliation and
including a range of patterns and severities of defoliation. The
model performed well for
E. globulus except in situations
where soil data or site history were poorly known, or where there
was likely to have been bud or tip damage (i.e. severe levels of
defoliation from pests such as
Gonipterus and autumn gum
moth).
There has been some initial validation work for Pinus
radiata, and this is ongoing.
Research staff are now working with industry colleagues to
investigate ways in which CABALA might be used operationally for
defoliation impact studies.
This work was co-funded by the Department of Climate Change.
