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The Monitor - Issue 5 - Tool for examining impact of defoliation on plantation productivity

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).

graph of stem volume of E globulus at Mawbanna

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

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.