Conservation Of Arboreal Marsupials Research Articles

The conservation of arboreal marsupials in the Albury‐Wodonga region of south‐eastern Australia

SummaryUrban expansion is a major cause of land use change and presents a significant threat to biodiversity worldwide. Agricultural land is often acquired by local councils and developers to expand urban growth boundaries and establish new housing estates. However, many agricultural landscapes support high biodiversity values, especially farmlands that feature mosaics of native vegetation and keystone habitat such as hollow‐bearing trees. In south‐eastern Australia, many arboreal marsupials including the threatened Squirrel Glider (Petaurus norfolcensis) have populations within peri‐urban zones of expanding rural cities. A key challenge to planners, developers and conservation organisations is the need to maintain habitat for locally rare and threatened species as land undergoes changes in management. Critical to the sustainable development of peri‐urban landscapes is a thorough understanding of the distribution, habitat requirements and resources available to maintain and improve habitat for species dependent on limited resources such as tree cavities. In this management report, we present background information on an integrated research programme designed to evaluate potential impacts of urban development on fauna in the Albury Local Government Area, NSW. We mapped hollow‐bearing trees, erected nest boxes and monitored arboreal marsupials. Information presented in this report provides a blueprint for monitoring arboreal marsupials, including threatened species in other developing regions, and will assist the Albury‐Wodonga local governments in future planning of sustainable living environments.

The status of hollow-bearing trees required for the conservation of arboreal marsupials in the dry sderophyll forests of south-east Queensland, Australia

At 38 sites in the dry sclerophylJ forests of south-east Queensland, Australia, hollow-bearing trees were studied to determine the effects of past forestry practices on their density, size and spatial distribution. The density of hollow-bearing trees was reduced at sites that had been altered by poisoning and ringbarking of unmerchantable trees. This was especially the case for living hollow-bearing trees that were now at densities too low to support the full range of arboreal marsupials. Although there are presently enough hollow-bearing stags (i.e., dead hollow-bearing trees) to provide additional denning and nesting opportunities, the standing life of these hollow-bearing stags is lower than the living counterparts which means denning and nesting sites may be limited in the near future. The mean diameter at breast height (DBH) of hollow-bearing stags was significantly less than that of living hollow-bearing trees. This indicated that many large hollow-bearing stags may have a shorter standing life than smaller hollow-bearing stags. Hollow-bearing trees appear to be randomly distributed throughout the forest in both silviculturally treated and untreated areas. This finding is at odds with the suggestion by some forest managers that hollow-bearing trees should have a clumped distribution in dry sclerophyll forests of south-east Queensland.

The conservation of arboreal marsupials in the montane ash forests of the central highlands of Victoria, south-eastern Australia. VIII. Landscape analysis of the occurrence of arboreal marsupials

We describe the results of landscape analysis of the occurrence of a suite of species of arboreal marsupials in the montane ash forests of the central highlands of Victoria, south-eastern Australia. The species targeted for study were: Yellow-bellied Glider ( Petaurus australis), Mountain Brushtail Possum ( Trichosurus caninus), Greater Glider ( Petauroides volans) and Leadbeater's Possum ( Gymnobelideus leadbeateri). Our analyses involved exploring statistical relationships between the presence/absence of these four species and compositional variables used to characterise the landscape within 20 and 80 ha circles surrounding each of 166, 3 ha, sites surveyed for arboreal marsupials. Many potential statistical models were examined for each of the four species targeted for analysis. With the exception of P. australis, the final model chosen was the null model; i.e. none of the landscape variables were statistically significant as predictors of the presence of animals at a site. In the case of P. australis, three measures of the landscape within the 80 ha circles surrounding our survey sites were found to be statistically significant: (1) the presence of old forest, (2) the steepness of the forest terrain, and, (3) the area of forest on different aspects. There was a significantly higher probability of detecting the species on northerly and westerly aspects, on either steep or flat terrain, and within circles supporting old growth montane ash forest. P. australis has a home range of 40–60 ha which is at least an order of magnitude larger than the other species of arboreal marsupials examined. Thus, the size of the 80 ha circle used to capture data on landscape composition matched the home range size of P. australis more closely than other species of arboreal marsupials examined in this study. This may, in part, explain why it was the only species for which landscape composition variables were found to be significant predictors of occurrence. Our findings tentatively suggest that changes in the spatial coverage of old growth forest that have resulted from past wildfires, post-fire salvage logging and more recent intensive and extensive clearfell logging operations, have created landscape patterns unsuitable for P. australis. The implications of our results for the conservation of the species are discussed. In addition, some difficulties were experienced in the use of landscape-scale data in our statistical analyses, such as identifying attributes of landscape composition that are biologically relevant to the taxa targeted for analysis. We briefly discuss the nature of these problems.

Potential impact of harvesting for the long-term conservation of arboreal marsupials

We used a simulation approach to study the trade-off between forest harvesting and the conservation of arboreal marsupials in managed eucalypt forests of south-eastern New South Wales (Australia). The EDEN gap model is used to predict tree biomass harvested and the resulting shifts in habitat quality (HQ) for arboreal marsupials under different harvesting scenarios. These harvesting scenarios generate a gradient of biomass harvested by varying rotation length and tree retention in different topographic positions. The results suggest that the shape of the curve of reduction of HQ along the harvesting gradient is very sensitive to topographic position and hence to the proportion of topographic units in the landscape. Consequently arboreal marsupial management in logged forests will be region-dependent as each region will have its own pattern of landscape complexity.

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 : D. B. Lindenmayer & H. P. Possingham, Biological Conservation, 73(3), 1995, pp 239–257

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 : D. B. Lindenmayer & H. P. Possingham, Biological Conservation, 73(3), 1995, pp 239–257

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.

The conservation of arboreal marsupials in the montane ash forests of the central highlands of Victoria, south-eastern Australia, VI. The performance of statistical models of the nest tree and habitat requirements of arboreal marsupials applied to new survey data

Statistical models are widely used as a tool to provide a concise description of data by identifying and quantifying relationships between key explanatory variables. The adequacy of the fit of such models to the data can be gauged by various diagnostic procedures. However, the performance of statistical models, when applied to new datasets, can yield valuable insights about the various assumptions that underpin such models and may identify potentially important new explanatory variables. In this study we describe the results of a field survey that was undertaken specifically to assess the performance of previously developed statistical models of the nest tree and habitat requirements of arboreal marsupials inhabiting the montane ash forests of the central highlands of Victoria, south-eastern Australia. The study involved comparing logit and Poisson regression models developed from surveys at 152 sites completed between 1983 and 1989 with a new dataset comprised of 55 sites that was gathered in 1992–1993. Our analyses demonstrated that most of the models developed in earlier studies performed reasonably well when they were applied to the recently collected data. Thus, for the two datasets, there were similarities in the statistical relationships between characteristics of trees with hollows and their occupancy by various species of arboreal marsupials. Similar results were recorded from assessments of the performance of the habitat models. Notably, for some species such as Leadbeater's possum, Gymnobelideus leadbeateri McCoy, there was greater congruence between the results of the two surveys than recorded in similar comparisons with data collected from retained linear strips (wildlife corridors). This finding further emphasizes previous observations that the species appears to be disadvantaged in narrow areas of linear habitat.

The conservation of arboreal marsupials in the montane ash forests of the central highlands of Victoria, South-Eastern Australia V. Patterns of use and the microhabitat requirements of the mountain brushtail possum Trichosurus caninus ogilby in retained linear habitats (wildlife corridors)

Hairtubing, a technique for detecting mammals, was used to census arboreal marsupials at 70 sites in the timber production montane ash forests of the central highlands of Victoria, south-eastern Australia. Of these sites, 41 were located in linear strips or wildlife corridors and the remaining 29 were in stands of contiguous montane ash forest. Four species of arboreal marsupials were detected in the hairtubing surveys but only one, the mountain brushtail possum Trichosurus caninus Ogilby, was recorded in sufficient numbers to allow subsequent analysis. Data derived for T. caninus from hairtubing studies were compared with those from earlier surveys where stagwatching was used to determine the presence and abundance of the species in retained linear strips. T. caninus was found to be absent from many retained strips during stagwatching surveys but was subsequently detected by hairtubing. Movement by animals into retained linear strips from surrounding areas of contiguous forest, probably whilst foraging, was the most logical explanation for this result. Statistical analyses revealed that T. caninus was most likely to move into strips that supported few trees with hollows and thus areas of poor habitat suitability where there were few resident animals. Such forays may represent an adoption of a retained area as part of an animal's home range. These findings suggest possible functional differences in the use of retained linear strips by T. caninus where some sites provide habitat for resident animals and others, of poorer habitat quality, are used by individuals that do not live in the strip. Within the survey sites, T. caninus was most likely to be detected by hairtubing in those plots where there were numerous tree ferns, Dicksonia antarctica and Cyathea australis, and where the trees Acacia dealbata and A. melanoxylon were present. Thus, some microhabitat features may influence the patterns of use by T. caninus within areas of retained forest. The implications of our results for wildlife conservation in timber production montane ash forests are discussed.

The conservation of arboreal marsupials in the montane ash forests of the central highlands of Victoria, South-east Australia, IV. The presence and abundance of Arboreal marsupials in retained linear habitats (wildlife corridors) within logged forest

Arboreal marsupials were censused in 49 retained linear habitats (wildlife corridors) that were excluded from timber harvesting in mountain ash Eucalyptus regnans F. Muell. and alpine ash E. delegatensis R. T. Bak. forests in the Central Highlands of Victoria, south-eastern Australia. The study sites varied in mean width from 30 to 264 m and were bounded by clearfelled and regenerated forests that were aged four years or younger. Of the 402 large trees with hollows that were measured and censused on the 49 study sites, a total of 69 animals was observed from 54 occupied trees, giving one occupied tree per 7·4 trees that were watched. The species of arboreal marsupials recorded during the study included greater glider Petauroides volans Kerr, mountain brushtail possum Trichosurus caninus Ogilby, feather-tail glider Acrobates pygmaeus Shaw, common ringtail possum Pseudocheirus peregrinus Boddaert, yellow-bellied glider Petaurus australis Shaw, sugar glider Petaurus breviceps Waterhouse and Leadbeater's possum Gymnobelideus leadbeateri McCoy. P. volans and T. caninus were the most commonly observed species and accounted for 78% of the animals seen. These species may survive better, at least in the short term, than others in linear strips that are retained after timber harvesting. Colonial and social species of arboreal marsupials that consume widely dispersed food such as saps and gums were uncommon, as predicted by the theory of central place foraging. The presence and abundance of arboreal marsupials in retained linear strips were compared with predictions from models of the habitat requirements of these species developed from sites in contiguous forest. These comparisons revealed that the presence of P. volans, P. breviceps and P. australis in retained linear strips was not significantly different from predictions derived from measures of the suitability of habitat in such areas. T. caninus was recorded at fewer sites than predicted, although the abundance of the species when present was not different from expected values. The endangered G. leadbeateri was recorded only once during the study, despite many sites providing apparently suitable habitat. Retained linear strips supported a significantly lower total abundance of arboreal marsupials than predicted from measures of habitat suitability. A combination of habitat parameters and other measured attributes of retained linear strips such as width and length were used to explain the variation in the presence and abundance of arboreal marsupials. The presence of T. caninus was influenced significantly by the number of trees with hollows and by the length of the site. P. volans was most likely to occur on sites with many trees with hollows, a westerly aspect and where there was no watercourse. Sites with the highest probability of supporting any species of arboreal marsupial occurred in E. regnans forests with numerous trees with hollows and which spanned the topographic sequence (e.g connected a ridge to a gully). The implications of our findings for the use, design and location of strips of retained linear habitat in timber production forests are discussed.

The conservation of arboreal marsupials in the montane ash forests of the Central Highlands of Victoria, South-East Australia: III. The habitat requirements of leadbeater's possum Gymnobelideus leadbeateri and models of the diversity and abundance of arboreal marsupials

Factors influencing the presence and abundance of leadbeater's possum Gymnobelideus leadbeateri McCoy and the diversity and abundance of other species of arboreal marsupials in montane ash forests were determined from logistic and Poisson regression analyses. The presence of G. leadbeateri was related to the number of trees with hollows and the basal area of Acacia spp. There was a positive correlation between the abundance of the animal and the number of trees with hollows, the quantity of decorticating bark and a negative correlation with the number of shrubs and the slope of the site. The diversity of arboreal marsupials was greatest on sites with a large number of trees with hollows, a high basal area of Acacia spp., a large quantity of decorticating bark and south- or east-facing sites. A model containing similar variables was developed for the abundance of arboreal marsupials. This model also produced a significant negative correlation with the number of stumps resulting from timber harvesting operations. Our findings highlight the deficiencies of current measures to conserve arboreal marsupials which are dependent on hollows in trees, when these forests are harvested by clear-felling.

The conservation of arboreal marsupials in the montane ash forests of the Central Highlands of Victoria, south-east Australia: II. The loss of trees with hollows and its implications for the conservation of leadbeater's possum Gymnobelideus leadbeateri McCoy (marsupialia: petauridae)

Leadbeater's possum, Gymnobelideus leadbeateri McCoy, a rare and endangered arboreal marsupial inhabiting the montane ash forests of the Central Highlands of Victoria, is dependent on hollows in mature and dead trees. The number of trees with hollows that had collapsed between 1983 and 1988 was assessed at 32 sites located in ash-type forests in the Central Highlands of Victoria, south-eastern Australia. The extent of decay amongst standing trees with hollows was also determined. A simple stochastic model of the decline and collapse of these trees was calculated from the data. The model was applied to data on trees with hollows collected from 497 other sites within the study region to predict their future abundance and availability over the next 75 years. Almost 18% of the total measured population of trees had collapsed in the 5-year interval between assessments. A subjective categorization of the form of the trees was the best predictor of the susceptibility to collapse. More senescent trees were those most vulnerable to collapse and they also exhibited the highest rates of decay. Stochastic models based on transition probabilities of trees with hollows predict that very few of the sites surveyed will support such trees in 50 years time and imply a severe future shortage of trees containing suitable nest hollows for wildlife until at least the end of the next century. Silvicultural practices which result in ash-type forests being clear-felled on a short-term (80–120 year) rotation will further accelerate and exacerbate the anticipated shortage. The implications of these effects for wildlife, particularly G. leadbeateri, are discussed.

The conservation of arboreal marsupials in the Montane ash forests of the central highlands of Victoria, Southeast Australia: I. Factors influencing the occupancy of trees with hollows

A total of 1125 trees with hollows on 152 sites in the montane ash forests of the Central Highlands of Victoria was observed for the presence of arboreal marsupials. One of every 3 trees was occupied by an arboreal marsupial and < 1% of these were inhabited by more than 1 species. Occupancy of the trees was significantly influenced by their characteristics and spacing, and by the aspect of the site and other measures of the suitability of forest habitat surrounding the tree. Timber harvesting practices result in montane ash forests being clear-felled on an 80–120 year rotation. Our results indicate that such silvicultural practices will have a detrimental impact on arboreal marsupials inhabiting montane ash forests.