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Long-term realised and projected growth impacts caused by autumn gum moth defoliation of 2-year-old Eucalyptus nitens plantation trees in Tasmania, Australia


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Rapley, LP, Potts, BM, Battaglia, M, Patel, VS and Allen, GR 2009 , 'Long-term realised and projected growth impacts caused by autumn gum moth defoliation of 2-year-old Eucalyptus nitens plantation trees in Tasmania, Australia' , Forest Ecology and Management, vol. 258, no. 9 , pp. 1896-1903 , doi: 10.1016/j.foreco.2009.06.036.

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Insect damage to production forests has the potential to reduce financial returns by retarding tree
growth and causing mortality, however, long-term realised quantification of these losses is rare. In order
to help elucidate economic damage thresholds for making spray decisions we capitalised on a natural
outbreak of autumn gum moth, Mnesampela privata, in a 2-year-old Eucalyptus nitens plantation.
Following the partial chemical control of this insect outbreak we measured the tree growth variables
diameter at breast height over bark and height of five differing tree defoliation classes for 75 months
following tree damage. At the end of this period a thresholdmodel was fitted to describe the relationship
between tree defoliation and realised tree wood volumes. The model revealed that realised stand wood
volume was not significantly affected up until defoliation exceeded 60% and then declined sharply after
this defoliation level was reached. Further support for this defoliation threshold was evident from
multiple comparisons among defoliation classes that showed 50% defoliated trees did not have
significantly different wood volume compared tomore lightly defoliated trees, but did have significantly
greater wood volume compared to trees that were 72% or more defoliated. To determine if the realised
differences in wood volume resulted in differences in yield over a plantation rotation the E. nitens growth
model NITGRO was used to on-grow trees to age 15 years for a ‘best case’ (type 1 growth response,
constant growth rates from last inventory until harvest) and ‘worst case’ (type 2 growth response,
divergent growth rates from last inventory until harvest) scenario. The threshold model was then fitted
to the outcomes of both scenarios and the economic consequences of defoliation were clearly dependent
on the growth function assumed.

Item Type: Article
Authors/Creators:Rapley, LP and Potts, BM and Battaglia, M and Patel, VS and Allen, GR
Keywords: Lepidoptera, Mnesampela privata, Eucalyptus nitens, Defoliation, Wood volume, Harvest implications
Journal or Publication Title: Forest Ecology and Management
ISSN: 0378-1127
DOI / ID Number: 10.1016/j.foreco.2009.06.036
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