The Conservation Of Arboreal Marsupials In The Montane Ash Forests Of The Central Highlands Of Victoria, South-Eastern Australia - VII. Modelling The Persistence Of Leadbeater's Possum In Response To Modified Timber Harvesting Practices

A computer model for Population Viability Analysis (PVA) was used to simulate the relationship between the persistence of populations of the endangered species, Leadbeater's possum, Gymnobelideus leadbeateri and the implementation of a range of possible modified timber harvesting practices in two wood production blocks within the montane ash forests of the central highlands of Victoria, south-eastern Australia. The results of our analyses revealed that under the existing conservation strategies there was a high probability of extinction over the next 150 years in both blocks. Given that timber production areas comprise more than 75% of the distribution of G. leadbeateri, our findings highlight a need for additional conservation measures to enhance the survival prospects of the species. The range of upgraded conservation strategies that were examined included (1) extending the rotation time between logging operations; (2) modifying silvicultural practices to increase the amount of forest retained within each harvested coupe; and (3) permanently withdrawing areas from wood production. All of each of these approaches were found significantly to reduce the probability of extinction of populations of G. leadbeateri. However, when the relative merits of the various strategies were compared, the permanent withdrawal of potential logging coupes from timber harvesting was predicted to be the most efficient approach. Importantly, this strategy would have a number of practical advantages including that it overcomes both (1) the logistic difficulties of ensuring the long-term survival of retained trees within logged areas; and (2) human safety issues arising from implementing modified silvicultural practices. This practical application of PVA to compare the merits of different potential management options has provided new information that will enhance present efforts to conserve G. leadbeateri in wood production areas

Modelling the impacts of wildfire on the viability of metapopulations of the endangered Australian species of arboreal marsupial, Leadbeater's Possum

Catastrophic events such as intensive wildfires have a major effect on the dynamics of some wildlife populations. In this investigation, the computer package ALEX (Analysis of the Likelihood of EXtinction), was used to simulate the impacts of wildfires on the persistence of metapopulations of the endangered species Leadbeater's possum (Gymnobelideus leadbeateri) which is restricted to the montane ash forests of the Central Highlands of Victoria. A range of scenarios was examined. First, the response of G. leadbeateri to tires in hypothetical patches of old growth forest of varying size was modelled. Metapopulation dynamics were then modelled in four existing forest management areas: the O'Shannassy Water Catchment and the Steavenson, Ada and Murrindindi Forest Blocks using GIS-derived forest inventory data on complex spatial arrangements of potentially suitable old growth habitat patches. The impacts of different fire frequencies and the proportion of forest area that was burnt in the Steavenson Forest Block and the O'Shannassy Water Catchment were examined. Finally, the combined impacts of both wildfires and post-fire salvage logging operations on the persistence of populations of G. leadbeateri were assessed. Our analyses indicated that, even in the absence of wildfires, populations of G. leadbeateri are very susceptible to extinction within single isolated habitat patches of 20 ha or less. The probability of persistence approached 100% in patches of 250 ha. The incorporation of the effects of wildfire was predicted to have a major negative impact on isolated populations of G. leadbeateri. In these cases, the probability of population extinction remained above 60%, even when a single patch of 1200 ha of old growth forest was modelled. In the absence of wildfires, there was a low probability of extinction of G. leadbeateri in the O'Shannassy Water Catchment where very large patches of old growth forest presently exist. The risk of extinction of the species was significantly higher in the Murrindindi and Ada Forest Blocks where there are lower total areas of, and significantly smaller, suitable habitat patches. Wildfires resulted in an increase in the predicted probability of metapopulation extinction in the four areas that were targeted for study. An investigation of the Steavenson Forest Block and the O'Shannassy Water Catchment revealed that the predicted values for the probability of extinction were sensitive to inter-relationships between the frequency of fires and the proportion of habitat patches that were burnt during a given fire event. The probability of extinction of G. leadbeateri was predicted to be lowest when there were frequent fires that burnt only relatively small areas of a given forest block. Conversely, the results of our analyses suggested that populations of the species are vulnerable to infrequent but intensive conflagrations that burnt a large proportion of the forest. The results of the suite of analyses completed in this study suggest hat four management strategies will be important for the long-term conservation of G. leadbeateri. (1) Attempts to suppress wildfires should be maintained as even the largest remaining areas of old growth forest may be susceptible to being burnt by repeated widespread wildfires that could result in localised and/or global extinction of the species. (2) Because the probability of population persistence is greatest in those areas that support more extensive stands of old growth forest, it will be important to grow relatively large patches of existing regrowth forest (over 50 ha) through to ecological maturity. This will be particularly important in some wood production forest blocks where there are only limited areas of old growth forest. (3) Patches that are set aside for the conservation of G. leadbeateri should be spatially separated to minimise the risk that all of the reserved areas in a region are destroyed in a single major fire event. (4) Salvage logging operations should be excluded from stands of old growth forest and reserved areas that are burnt in a wildfire. This is because such activities can have a major negative impact of the development of suitable habitat for G. leadbeateri

Proposed recommendations : Mallee study area /

0724109242 (paperback) (ISBN). "March 1976".; Index indicating National Library of Australia holdings, in an online version at: http://nla.gov.au/nla.map-vn2766744; Library's NL copy does not contain maps.Mallee study are