Jenny L. Nelson’s research while affiliated with Victoria State Government - Department of Environment, Land, Water and Planning and other places

Large wildfires have the potential to create heterogeneous landscapes in forest ecosystems. Range-restricted species in fire-prone regions have evolved to persist in the face of periodic disturbance due to wildfire. However , the factors that enable them to do so are often poorly understood. Whether post-fire population recovery is driven by survival of individuals within the burnt area (in situ recovery) or by recolonisation from unburnt habitat outside the fire perimeter (ex situ recovery), and over what timeframe this occurs, is valuable knowledge for conservation management. Understanding post-fire population dynamics is important when considering whether management interventions are required to prevent local extinctions. We examined the influence of fire-derived landscape context on site occupancy by the critically endangered Leadbeater's possum Gymnobelideus leadbeateri in southeastern Australia, 6-11 years after a large wildfire in 2009. Our aim was to assess whether site occupancy was influenced by fire extent in the local landscape, distance from unburnt habitat outside the fire perimeter, and/or pre-fire disturbance history. We used arboreal camera trapping to survey Leadbeater's pos-sums within the burnt area, using 732 cameras at 245 sites. We used occupancy modelling to estimate the effects on site occupancy of (1) unburnt habitat surrounding sites (500 m radius), (2) distance from unburnt habitat at the fire perimeter, and (3) whether the site had been disturbed by either fire or timber harvesting in the decades prior to the 2009 fire. Leadbeater's possums were detected at 78 of the 245 sites (32 %). Site occupancy was positively influenced by the presence of unburnt habitat within 500 m, and was higher at sites that had experienced disturbance between the 2009 fire and the previous major wildfire in 1939. Proximity to unburnt habitat outside the fire perimeter did not influence occupancy. Our results suggest that population recovery was driven primarily by in situ survival and recovery, rather than via recolonisation from source populations outside the burnt area. Our findings indicate that Leadbeater's possum populations are more likely to recover from fires that are more heterogeneous in their severity, leaving relatively more unburnt patches within their perimeter. Post-fire management interventions such as translocation to facilitate population recovery are likely unnecessary for this species, provided surviving individuals have spatial continuity of habitat to enable recolonisation. Management strategies aimed at the retention of unburnt patches within the footprint of future fires will likely promote the post-fire recovery of arboreal mammal species in fire-prone forests, particularly under a changing climate with increased frequency and intensity of wildfires.

Within its core highland range, Leadbeater’s possum (Gymnobelideus leadbeateri) occurs predominantly in tall montane ash forest dominated by Eucalyptus regnans, E. delegatensis and E. nitens. To improve predictive modelling of suitable habitat, we surveyed ash/non-ash ecotones and also explored the species’ recently extended eastern distribution. We detected Leadbeater’s possums at 19 sites, including six in non-ash forest dominated by E. dalrympleana, E. viminalis or E. kybeanensis. This extends its known distribution by 5.5 km and appears to delineate the north-eastern limit of its range. Our results add to previous findings indicating Leadbeater’s possums have slightly broader range limits and habitat flexibility than previously thought.

Indirect surveillance methods, such as remote cameras and acoustic monitoring, are increasingly used in ecological surveys. The time to deploy these devices includes initial setup, possible maintenance, retrieval and then a potentially large investment in the processing of the collected data. Thus, costs will increase with both the number of sites at which devices are deployed and the time they remain in the field, creating a trade-off between these factors when aiming to maximise the number of sites with detections. Here we examine a scenario in which a target species occupies a proportion of the possible survey sites(psi), establishing a new site has a fixed cost (c), each survey of a site entails a cost per unit of survey effort (t), there is imperfect detection of the species during each survey such that the probability of failing to detect the species with a unit of survey effort is when the species is present, and there is a total budget that can be allocated to establishing and surveying sites (B). We show that the expected number of sites with detections is maximised by surveying each site with a particular amount of survey effort (v) that depends only on q and c. This analytical result can be used by researchers to optimise their survey effort prior to field work and provide opportunities for optimal allocation of their survey budget. We illustrate the method with an application to surveys of the threatened Leadbeater’s Possum (Gymnobelidus leadbeateri).

ContextDetermining population size or density is often fundamental for wildlife conservation. For nocturnal species, indices are commonly used in place of abundance estimates, with spotlighting indices (e.g. sighting rate per km) being prevalent. Distance sampling is a collection of techniques that provide estimates of wildlife abundance from line-transect data, by correcting raw counts for imperfect detection. These methods have rarely been used to assess the abundance of nocturnal arboreal mammals. AimsTo develop and evaluate a method for estimating the abundance and density of nocturnal arboreal mammals using double-observer distance sampling, and to apply the approach to a survey of the southern greater glider (Petauroides volans) in the Strathbogie Ranges, Victoria, Australia. Methods Two observers, 15–20 min apart, surveyed 25 randomly located 500 m transects, and recorded greater gliders using spotlights and binoculars. Densities and abundances were derived from the line-transect data by using mark–recapture distance sampling (MRDS) models and were compared with conventional distance sampling analysis (CDS). Key resultsUsing the double-observer approach, we estimated an overall density of 0.96 gliders ha−1 (95% CI 0.60–1.50), giving a population estimate of 24 575 greater gliders across the Strathbogie Ranges (25 865 ha, 95% CI 15 620–38 661). The corresponding estimates for the study area derived using CDS applied to either both observers’ observations or to the first observer’s observations only, were 87% and 53% respectively, of the MRDS estimate. The analysis confirmed that the probability of detection of gliders along the transect line was less than one, justifying the use of the double-observer method to obtain accurate estimates of abundance. Conclusions The low detectability of greater gliders means that uncorrected spotlight counts will underestimate abundance, as will CDS. The double-observer method corrects for the negative bias associated with raw counts, enabling more accurate estimation of abundance for survey, monitoring and management purposes. ImplicationsWe recommend that double-observer distance sampling is adopted as a standard technique for estimating the abundance of greater gliders. The double-observer method potentially has wider relevance for assessing population size of other arboreal mammals, providing the assumptions of the approach can be met.

Increasing impacts of climatic change and anthropogenic disturbances on natural ecosystems are leading to population declines or extinctions of many species worldwide. In Australia, recent climatic change has caused population declines in some native fauna. The projected increase in mean annual temperature by up to 4°C by the end of the 21st century is expected to exacerbate these trends. The greater glider (Petauroides volans), Australia’s largest gliding marsupial, is widely distributed along the eastern coast, but has recently experienced drastic declines in population numbers. Its association with hollow‐bearing trees, used for nesting, has made it an important species for the conservation of old‐growth forest ecosystems. Fires and timber harvesting have been identified as threats to the species. Greater gliders have disappeared however from areas that have experienced neither raising questions about the role of other factors in their decline. A unique physiology and strict Eucalyptus diet make them vulnerable to high temperatures and low water availability. As such, climatic conditions may drive habitat selection and recent climatic trends may be contributing to observed population declines. Using presence:absence data from across its distribution in Victoria, coupled with high spatial and temporal resolution climatic data and machine‐learning modeling, we tested the influence of climatic, topographic, edaphic, biotic, and disturbance variables on greater glider occupancy and habitat suitability. We found that climatic variables, particularly those related to aridity and extreme weather conditions, such as number of nights warmer than 20°C, were highly significant predictors of greater glider occurrence. Climatic conditions associated with habitat suitability have changed over time, with increasing aridity across much of its southeastern distribution. These changes in climate are closely aligned with observed population declines across this region. At higher elevation, some areas where the greater glider is observed at high densities, conditions have become wetter, which is improving habitat quality. These areas are of growing significance to greater glider conservation as they will become increasingly important as climatic refugia in the coming decades. Protecting these areas of habitat will be critical for facilitating the conservation of greater gliders as the broader landscape becomes less hospitable under future climatic change.