ADVICE which led to the Leadbeater's Possum being classed as "critically endangered" has been criticised as flawed by leading Australian forestry scientists.
In a submission to the federal government, The Institute of Foresters of Australia contended not all available evidence was considered by the Threatened Species Scientific Committee, and that the body relied on erroneous and questionable assumptions to make its April 2015 determination.
The scientists said the TSSC's assumptions, such as the extent of possum habitat, population density, actual population numbers of the possum, and the impacts of harvesting and wildfire, were not based on sound science.
The TSCC examined five criteria population numbers, geographic distribution, area of occupation, number of mature individuals and probability of extinction with the 'critically endangered' determination based on population numbers.
"Under the other four criteria the species would be considered vulnerable or endangered," the paper read.
"...the identification of at least 400 new colonies during 2014-16 (many being in young regrowth forests) would perhaps double the estimates used by the TSCC in its determination."
Given the difficulty in surveying the possum, the IFA said the TSCC used habitat as a surrogate for population numbers.
To be classified as critically endangered, a species must lose more than 80 per cent of its population over the last three generations, 18 years in this case.
The TSCC's decision was based on habitat lost due to wildfire and timber harvesting, and the high likelihood of a further 80 per cent reduction in habitat due to wildfire over the next 18 years.
IFA contended in its paper that the assessment was flawed because of estimates of habitat area, habitat occupancy and the unsupported conclusion on stopping timber harvesting.
The IFA said estimates of suitable and occupied habitat for the possum varied widely, and the TSCC suggested large parts of 'suitable habitat' were not occupied by the possum, with distribution patchy.
"This is hardly surprising when 'occupancy' is assessed at the fine scale of a few hectares," the IFA said.
"Most bird and mammal species would show low occupancy rates if assessed by snapshot surveys at such a fine scale."
Further, the probability that an individual old tree is used by a possum is greater when these trees are sparsely distributed among regrowth rather than densely clumped.
Therefore, the 'predicted suitable habitat' area used by the TSCC was likely to be too low.
The TSCC relied on personal communication from one scientist to estimate habitat loss since 1989, inferring a proportional loss of habitat in the 18 years since 1989.
"These estimates were not subject to independent verification using current Victorian government data on the status of the habitat," the IFA said.
"Little use appears to have been made of the extensive data collected on numbers of LBP at known sites that have been monitored regularly over many years."
The IFA also said the TSCC underestimated the possum's adaptability.
About four yeas ago, not long after the catastrophic 2009 fires, the TSCC did not consider the known ability of the species to recolonise regrowth after wildfire or logging as long as suitable denning habitats remained available.
"These can be in live or dead old trees, or artificial hollows, even at relatively low densities. Hence the analyses provide a pessimistic view of the decline in species numbers," the IFA said.
"Population cycles are a feature of many wildlife species ... LBP numbers will increase as regrowth develops after wildfire or logging, as long as suitable hollows remain available in remaining live or dead old trees, or artificial hollows."
The IFA said there was much evidence that LBP could occupy 10-year-old regrowth forests, supported by recent surveys.
The identification of new colonies that would perhaps double estimates of species numbers "warrants a review of the conservation status of the species".
The IFA said wildfire was the main threat to possum habitat, but concluded, without justification, that stopping timber harvesting was the best way to halt further decline.
As there was already substantial areas of 1939 regrowth in national parks and other reserves, ceasing harvesting would provide a marginal increase in potential habitat.
Also, logging of old and hollow-bearing trees had been prohibited since the 1990s.
"Well-managed harvesting on a limited area can provide better capacity for effective fire management than passively managed parks and reserves," the scientists said.
The IFA said timber harvesting only occured on a limited part of potential habitat, and the TSCC ignored current management practices.
These included intensive coupe surveys, protection of sites where colonies are located, and silviculture that retains habitat trees and clumps within managed stands.
Other effective measures were nest boxes and artificial hollows.
The IFA authors also strongly backed management actions such as translocation establishing sub-LBP populations outside the region and accelerated hollow development or the wider use of nest boxes.
"The latter measures are needed to address predicted short-term shortage of hollows in the most suitable habitats for LBP, which include mixed-age and regrowth forests," the scientists said.
The IFA said it strongly supported measures to increase the population and the conservation of the Leadbeater's Possum, but the measures needed to be based on sound science and the best available information, rather than assumption.