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plantations have been established in Tasmania since the late 1960s for E. nitens (C Dare,
pers. comm.) and the mid-1990s for E. globulus (Parsons et al., 2006).
The number of insect herbivore species or species groups on E. globulus/ nitens reported over time
from the Green Triangle, south-west WA and Esperance (WA) were compiled by the Industry Pest
Management Group (IPMG). The information on species richness in WA was largely taken from
data collected using fogging (1999–2002; Loch, 2006) and from light trapping (2003–2008;
Matsuki, 2006a, updated in 2009). For the Green Triangle, the information was taken from data
collected from light trapping (2006–2009; Matsuki, 2008c, updated in 2009). For WA and the
Green Triangle, additional data was sourced from insect population assessments by Albany
Plantation Forestry Company (APFL), Great Southern Limited (now Alberta Investment
Management Corp. and Australia New Zealand Forest Fund), Hansol PI (now Great Southern
Timberholdings), Timbercorp (now Australian Bluegum Plantations), and WA Plantation Resources
(WAPRES). A database was assembled on insect observations and collections and also used to
supplement the information. Note that there are many undescribed species, and identification of
species is continuing (see Acknowledgements).
For Tasmania, insect herbivore records from E. globulus/ nitens plantations were compiled from
Forestry Tasmania’s Forest Health database. This database contains records from the year 2000
onwards and includes all records of insects collected from the two plantation species, not just
species causing damage. Records of species before 2000 were compiled from interviews with forest
entomologists responsible for eucalypt plantation health in Tasmania at that time: David de Little
(Gunns Ltd) and Dick Bashford (Forestry Tasmania). Consequently it was anticipated that these
data were reliable for insect herbivore events that caused moderate to severe damage only, but not
for insects that caused little damage. To address this imbalance, data for the number of insect
herbivore species or species groups collected on E. nitens over time were compiled from Forestry
Tasmania’s Tasmanian Forest Insect Collection database (Grove, 2010). When interpreting the
results it is important to consider that the RWG7 datasets are not entirely independent of the
regional datasets because they share many authors. Eucalypt plantation estate data were sourced
from annual national plantation inventory updates (Parsons et al., 2006; Gavran & Parsons, 2010).
Analyses
Linear regression was used to test whether the number of insect herbivore records for each year was
correlated with the total area of the plantation estate, and the area of eucalypt plantations for the
southern Australian states. The number of insect herbivore records in each of three damage classes
(Table 1) was also correlated against area of new plantations and year. New plantations were those
planted in the last year (Parsons et al., 2006). Before conducting these analyses, the five variables
(total herbivore records, three damage classes and plantation area) were tested for temporal
autocorrelation with the autocorrelation function for up to three temporal lags. The area of new
plantations was distinguished from the total area of eucalypt plantations because juvenile-phase
foliage is preferred over adult-phase foliage by some insect herbivores, and seedlings are more
susceptible to insect damage (de Little et al., 2008).
For the regional databases, the degree of tree damage was defined as per Table 1, except that a
distinction was made between locally severe and widespread severe damage. For the most
damaging insect herbivores in each region, tables were created to track the severity of insect
herbivore damage in each sub-region across space and time. The data for the insect herbivores
causing the greatest damage were analysed in each sub-region. For each of these insect herbivores,
CRC for Forestry Technical Report 216: November 2011
Are insect herbivores in eucalypt plantations a worsening problem? 4