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Unburnt refugia support post-fire population recovery of a threatened arboreal marsupial, Leadbeater’s possum
Abstract
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.
... In a study on Leadbeater's Possum (Gymnobelideus leadbeateri) in South-Eastern Australia, Durkin et al. [85] found that population recovery depended mainly on in situ survival and not external recolonisation. A study in Victoria conducted by Berry et al. [86] found that refuges of unburnt peninsulas extending into burnt areas helped some species to persist within extensively burnt landscapes (including the mountain brushtail possum, Trichosurus cunninghami) but not others (such as the greater glider, Petauroides volans). ...
Habitat loss due to wildfire is an increasing problem internationally for threatened animal species, particularly tree-dependent and arboreal animals. The koala (Phascolartos cinereus) is endangered in most of its range, and large areas of forest were burnt by widespread wildfires in Australia in 2019/2020, mostly areas dominated by eucalypts, which provide koala habitats. We studied the impact of fire and three subsequent years of recovery on a property in South-East Queensland, Australia. A classified Differenced Normalised Burn Ratio (dNBR) calculated from pre- and post-burn Sentinel-2 scenes encompassing the local study area was used to assess regional impact of fire on koala-habitat forest types. The geometrically structured composite burn index (GeoCBI), a field-based assessment, was used to classify fire severity impact. To detect lower levels of forest recovery, a manual classification of the multitemporal dNBR was used, enabling the direct comparison of images between recovery years. In our regional study area, the most suitable koala habitat occupied only about 2%, and about 10% of that was burnt by wildfire. From the five koala habitat forest types studied, one upland type was burnt more severely and extensively than the others but recovered vigorously after the first year, reaching the same extent of recovery as the other forest types. The two alluvial forest types showed a negligible fire impact, likely due to their sheltered locations. In the second year, all the impacted forest types studied showed further, almost equal, recovery. In the third year of recovery, there was almost no detectable change and therefore no more notable vegetative growth. Our field data revealed that the dNBR can probably only measure the general vegetation present and not tree recovery via epicormic shooting and coppicing. Eucalypt foliage growth is a critical resource for the koala, so field verification seems necessary unless more-accurate remote sensing methods such as hyperspectral imagery can be implemented.
For many cryptic mammal species, limited distributional data restrict the scope or effectiveness of conservation actions, particularly in relation to habitat protection and/or management. The critically endangered Leadbeater’s possum illustrates this, with wet forests throughout its range impacted by logging and bushfire. The possum’s habitat has been subject to major disturbance and degradation over recent decades; however, the cryptic behaviour of the species has meant population trajectories have been difficult to monitor. Since 2012, surveys for the possum have been greatly expanded, predominantly based around camera trapping. This paper examines outcomes following a decade of targeted camera trapping for this high-profile threatened species. There have been 1143 camera trapping detections of Leadbeater’s possum since 2012, representing 57% of all detections over this period. For comparison, there were just 274 detections of the species over a comparable period during the preceding decade using all other survey techniques. The substantial increase in records reflects greater survey effort, but also the effectiveness of baited camera traps at detecting this cryptic mammal. As a consequence, we have greatly improved understanding of the species’ distribution within its core range following major bushfire in 2009. These detection data have informed some aspects of forest management, including the establishment of small logging exclusion areas. Other applications of camera traps have included directing them at dens, providing a non-invasive means of monitoring translocated individuals and reproductive success. Several important caveats regarding camera trapping surveys are discussed, particularly that detection/non-detection data may be insensitive at detecting population declines for communally-denning species such as Leadbeater’s possum, where abundance may change more readily than occupancy. A risk accompanying the proliferation of camera trapping is over-reliance on rapid, one-off camera surveys that fail to provide the in-depth insights on demography and population dynamics required to inform effective management of threatened species. This case study highlights the importance of robust survey and monitoring data to inform species conservation planning and management. The results also demonstrate that camera trapping can be as effective and efficient in determining occupancy for some arboreal mammals as it is for terrestrial species, where it is more commonly applied.
The loss of open habitats in Europe has led to severe declines in birds associated with these habitats. However, certain ecological disturbances reverse the trend towards afforestation and create appropriate conditions for open-habitat species. Yet, open-habitat bird occupancy dynamics after disturbance depend on a complex combination of as-yet poorly studied factors. We analysed the colonization patterns and post-fire time-window of occurrence of open-habitat species along 687 transects in 68 burnt areas over a period of 11 years. During the study, 8345 individuals belonging to 22 open-habitat birds were detected. Species richness was related to an increased time elapsed since the fire, fire severity and proximity of potential population sources. Many species changed across the 11 years post-fire. Some species like the tawny pipit and the ortolan bunting, showed time lags affecting the timing of local extinction. Water deficit played a significant role in bird occurrence and six species benefited from drier conditions. Open-habitat species were more frequently detected in burnt areas near previously occupied areas and in severely burnt areas. Our results support the hypothesis that fire plays a critical role in the distribution dynamics of open-habitat species. Peak number of species was reached rapidly, between two and 6 years after fire, although a few species showed their peak abundance later on. An appropriate strategy for favouring open-habitat specialists in these landscapes, while reducing the risk of large wildfires, should prioritize integrated fire management to generate patches of different fire ages.
Context Fire severity and frequency is predicted to increase over the remainder of the 21st century in Australia’s temperate forests; therefore, the effects of fire severity on forest-dependant species is of major conservation concern. Aims Determining the short-term (<1 year) effect of fire severity on a forest-dependant species, the greater glider, Petauroides volans, in Monga National Park, south-eastern New South Wales. Methods Three fire-severity classes were investigated, namely, low (canopy unburnt), moderate (partial canopy burn) and high (complete canopy consumption). Fifteen randomly allocated sites were visited in total, with five sites in each fire-severity class being visited on three separate occasions. Spotlighting of two off-track transects per site was completed over a 4-week period by using multi-covariate distance sampling (MCDS) to estimate greater glider densities at each fire-severity class. Key results An overall mean greater glider density estimate of 0.456 ha−1 (95% confidence interval (CI) 0.256–0.654 ha−1) was calculated across all sites in Monga National Park. Density estimates varied among fire-severity classes; low 0.779 ha−1 (95% CI 0.358–1.692 ha−1), moderate 0.472 ha−1 (95% CI 0.262–0.848 ha−1), and high 0.077 ha−1 (95% CI 0.0142–0.414 ha−1). Conclusions Distance sampling estimates suggested that areas affected by high-severity fire have lower densities of greater gliders. Implications The importance of areas experiencing low fire severity as a source of greater glider refugia during wildfire events is evident. Under a changing climate, frequent major wildfire events may significantly affect population viability of greater gliders if insufficient time between fires allow for population recovery.
Phone (03) 9450 8600 Website: www.depi.vic.gov.au/ari
Arboreal camera trapping is a burgeoning method providing a novel and effective technique to answer research questions across a variety of ecosystems, and it has the capacity to improve our understanding of a wide range of taxa. However, while terrestrial camera trapping has received much attention, there is little guidance for dealing with the unique challenges of working in the arboreal realm.
Our review draws on the expertise of researchers from six continents and the broader literature to investigate the advantages and disadvantages of arboreal camera trapping, and challenges to consider when using this technology. We also include mini‐guides with detailed information on the current arboreal camera trap literature, mounts used to install arboreal cameras, tree climbing pointers and safety tips, methods for deploying cameras without climbing, and tips for managing interference with camera function.
We find that arboreal camera traps have been most commonly used in the study of mammals in forests; however, there is potential for this method to be applied to a broad range of habitats including urban areas, and taxa such as birds, amphibians, invertebrates, and plants. Methods in arboreal camera trapping could be improved by developing a greater understanding of the factors affecting detection of species. The most common challenges of arboreal camera trapping are camera placement and camera site access. These can be overcome by understanding correct camera orientation, managing potential sources of interference in front of cameras, utilizing appropriate cameras mounts and training researchers properly.
Given the benefits and opportunities presented by arboreal camera trapping, it is likely to become an ever‐more popular method of studying arboreal species and systems. The information synthesized in this review provides guidance for future studies to help direct more reliable and robust ecological inferences from arboreal camera trapping.
Aim
As climate change intensifies and wildfire frequency and scale increase, it is critical we develop a robust understanding of how species recover from these major disturbances. Here, we aim to determine whether source populations for recovery following large‐scale intense wildfires are derived from either in situ survival, or immigration from surrounding unburnt areas (ex situ). Secondly, we sought to determine whether habitat elements (e.g., logs) within the landscape facilitate in situ survival of small mammals during fires.
Location
Grampians National Park, south‐eastern Australia.
Methods
We used long‐term post‐fire small mammal monitoring to investigate sources of recovery for small mammals, and camera trapping and habitat surveys immediately following large intense wildfires to assess evidence for and drivers of post‐fire survival.
Results
We found no relationship between distance to unburnt vegetation and the occurrence of any native species, suggesting that in situ survival is the probable mechanism for recovery of post‐fire mammal populations, compared with immigration from external unburnt areas. We also show that key habitat elements such as rocks and large trees were associated with the occurrence of several species immediately post‐fire, suggesting a role for these features in facilitating the survival of species during and following fire.
Main conclusions
We present evidence for post‐fire recovery being driven by in situ survival. In situ survival is facilitated by small unburnt patches and habitat elements in burnt areas. These surviving individuals become the founders for subsequent post‐fire population recovery. Given that globally we are seeing increasingly frequent large‐scale wildfires driven by climate change, the capacity for in situ survival will help mitigate some of the fire‐related impacts of climate change.
Fire drives animal population dynamics across many ecosystems. Yet, we still lack an understanding of how most species recover from fire and the effects of fire severity and patchiness on recovery processes. This information is crucial for fire‐mediated biodiversity conservation, particularly as fire regimes change globally.
We conducted an experiment to test whether post‐fire recovery is driven by in situ survival or recolonisation, and to determine whether this varies with fires of increasing percentage area burnt (burn cover) and severity. We used the pale field rat Rattus tunneyi as a model, because it represents the extinction process for a suite of mammal species suffering population collapse across Australia's northern savannas. Our treatments spanned a gradient from patchy, low severity fires (simulating early dry season management burns) to thorough, high severity fires (simulating wildfires). We performed capture–mark–recapture, vegetation and aerial surveys before, 6 weeks after and 1 year after fire.
Six weeks after fire, pale field rats were only captured in unburnt patches of vegetation, and capture rates were proportional to the amount of unburnt habitat. One year later, both vegetation and pale field rat populations recovered across all sites. However, population recovery after low severity fires was likely achieved through in situ survival and reproduction in unburnt micro‐refuges, compared to recolonisation driving recovery after high severity fires.
Synthesis and applications. Pale field rat persistence is strongly dependent on the retention of unburnt habitat patches within fire‐affected areas. Management strategies that increase micro‐refugia within burnt areas may facilitate pale field rat population recovery. Globally, building recovery mechanisms into fire management will be vital for supporting the long‐term persistence of fire‐affected species.
Fire's growing impacts on ecosystems
Fire has played a prominent role in the evolution of biodiversity and is a natural factor shaping many ecological communities. However, the incidence of fire has been exacerbated by human activity, and this is now affecting ecosystems and habitats that have never been fire prone or fire adapted. Kelly et al. review how such changes are already threatening species with extinction and transforming terrestrial ecosystems and discuss the trends causing changes in fire regimes. They also consider actions that could be taken by conservationists and policy-makers to help sustain biodiversity in a time of changing fire activity.
Science , this issue p. eabb0355
Quantifying the long‐term population trajectory of species and the factors affecting these trends is a fundamental part of animal conservation. We describe the results of a long‐term investigation of temporal changes in the occurrence of arboreal marsupials in the wet eucalypt forests of south‐eastern Australia. The assemblage includes habitat specialists such as the vulnerable greater glider Petauroides volans and the critically endangered Leadbeater’s possum Gymnobelideus leadbeateri, as well as common and widespread taxa. Using data gathered between 1997 and 2018, we quantified relationships between site occupancy of four marsupial species and spatio‐temporal site and landscape‐level variables, including the number of hollow‐bearing trees at a site, and the extent of fire and logging in the surrounding landscape. We found evidence that: (1) The number of hollow‐bearing trees (which are critical den sites for arboreal marsupials) has declined substantially in the past two decades. (2) There was a decline in all species of arboreal marsupials. (3) The presence of all species of arboreal marsupials was positively linked to the number of large old hollow‐bearing trees at a site. (4) The extent of logging disturbance in the landscape surrounding a site had a positive impact on the sugar glider Petaurus breviceps but a negative effect on Leadbeater’s possum. This suggests that ongoing logging will have further negative impacts on Leadbeater’s possum. (5) The presence of the greater glider and sugar glider declined with increasing amounts of fire in the landscape. Negative fire effects are a concern as montane ash forests are increasingly susceptible to high‐severity wildfires. Stronger efforts are needed to reduce the extent and frequency of logging and fire disturbance in mountain ash forests to protect arboreal marsupial populations.
Vegetation fires are an essential component of the Earth system but can also cause substantial economic losses, severe air pollution, human mortality and environmental damage. Contemporary fire regimes are increasingly impacted by human activities and climate change, but, owing to the complex fire–human–climate interactions and incomplete historical or long-term datasets, it is difficult to detect and project fire-regime trajectories. In this Review, we describe recent global and regional trends in fire activity and examine projections for fire regimes in the near future. Although there are large uncertainties, it is likely that the economic and environmental impacts of vegetation fires will worsen as a result of anthropogenic climate change. These effects will be particularly prominent in flammable forests in populated temperate zones, the sparsely inhabited flammable boreal zone and fire-sensitive tropical rainforests, and will contribute to greenhouse gas emissions. The impacts of increased fire activity can be mitigated through effective stewardship of fire regimes, which should be achieved through evidence-based fire management that incorporates indigenous and local knowledge, combined with planning and design of natural and urban landscapes. Increasing transdisciplinary research is needed to fully understand how Anthropocene fire regimes are changing and how humans must adapt.
Background
Wildfires affect vegetation structure, functions, and other attributes of forest ecosystems. Among these attributes, bird assemblages may be influenced by the distance from undisturbed to fire-disturbed forests. Information about this influence is essential for designing management plans aimed at conserving birds’ diversity in undisturbed forests, which contributes to their sustainability. In Northwest Argentina, timber extraction and man-caused fires threaten the sustainability of Southern Andean Yungas forests. In this region, we evaluated, in relation to a reference unburned forest, the effects of close and distant fire-disturbed patches on bird assemblages, exploring also relationships between burned and unburned forest structures on bird assemblages. On each site, we determined forest structural variables, and twice per year, from 2015 to 2017, we recorded birds seen or heard on every site, from dawn to 1000 hours, at 30 0.5 ha counting points.
Results
Abundance and richness of bird species were lower in the unburned reference site than in close- and distant-burned sites; the farther the distance of burned sites to the unburned site, the less similarity in bird assemblages. Bird assemblage abundance appeared to be associated with snag height and basal area. However, bird species in mature forests were present at all sites and outnumbered those typically found in forest edges, or secondary or disturbed forests.
Conclusions
Connected areas between unburned and burned forest patches provide habitat for birds living in both environments. Preventing forest fragmentation by reducing the number and size of wildfires, promoting selective timber logging, and banning post-fire snag removal will help promote suitable habitat for different bird assemblages and contribute to Yungas forests’ sustainability. This study is the first step toward understanding how fire-patch distances to unburned forests may affect bird assemblages in subtropical Southern Andean Yungas forests in South America and provide a basis for comparison with other subtropical ecosystems around the world.
Aim
Over the past several decades, wildfires have become larger, more frequent, and/or more severe in many areas. Simultaneously, anthropogenic ignitions are steadily growing. We have little understanding of how increasing anthropogenic ignitions are changing modern fire regimes.
Location
Conterminous United States.
Time period
1984–2016.
Major taxa studied
Vegetation.
Methods
We aggregated fire radiative power (FRP)‐based fire intensity, event size, burned area, frequency, season length, and ignition type data from > 1.8 million government records and remote sensing data at a 50‐km resolution. We evaluated the relationship between fire physical characteristics and ignition type to determine if and how modern U.S.A. fire regimes are changing sensu stricto given increased anthropogenic ignitions, and how those patterns vary over space and time.
Results
At a national scale, wildfires occur over longer fire seasons (17% increase) and have become larger (78%) and more frequent (12%), but not necessarily more intense. Further, human ignitions have increased 9% proportionally. The proportion of human ignitions has a negative relationship with fire size and FRP and a positive relationship with fire frequency and season length. Areas dominated by lightning ignitions experience fires that are 2.4 times more intense and 9.2 times larger. Areas dominated by human ignitions experience fires that are twice as frequent and have a fire season that is 2.4 times longer. The effect of human ignitions on fire characteristics varies regionally. Ecoregions in the eastern U.S.A. and in some parts of the coastal western U.S.A. have no areas dominated by lightning ignitions. For the remaining ecoregions, more intense and larger fires are associated with lightning ignitions, and longer season lengths are associated with human ignitions.
Main conclusions
Increasing anthropogenic ignitions – in tandem with climate and land cover change – are contributing to a ‘new normal’ of fire activity across continental scales.
Fire refugia are landscape elements that remain unburned or minimally affected by fire, thereby supporting postfire ecosystem function, biodiversity, and resilience to disturbances. Although fire refugia have been studied across continents, scales, and affected taxa, they have not been characterized systematically over space and time, which is crucial for understanding their role in facilitating resilience in the context of global change. We identify four dichotomies that delineate an overarching conceptual framework of fire refugia: unburned versus lower severity, species-specific versus landscape-process characteristics, predictable versus stochastic, and ephemeral versus persistent. We outline the principal concepts underlying the ecological function of fire refugia and describe both the role of fire refugia and uncertainties regarding their persistence under global change. An improved understanding of fire refugia is crucial to conservation given the role that humans play in shaping disturbance regimes across landscapes.
On interannual to decadal time scales, the climate mode with many of the strongest societal impacts is the El Niño–Southern Oscillation (ENSO). However, quantifying ENSO's changes in a warming climate remains a formidable challenge, due to both the noise arising from internal variability and the complexity of air-sea feedbacks in the tropical Pacific Ocean. In this work, we use large (≥30-member) ensembles of climate simulations to show that anthropogenic climate change can produce systematic increases in ENSO teleconnection strength over many land regions, driving increased interannual variability in regional temperature extremes and wildfire frequency. As the spatial character of this intensification exhibits strong land-ocean contrasts, a causal role for land-atmosphere feedbacks is suggested. The identified increase in variance occurs in multiple model ensembles, independent of changes in sea surface temperature variance. This suggests that in addition to changes in the overall likelihoods of heat and wildfire extremes, the variability in these events may also be a robust feature of future climate.
Rodent populations respond quickly to changes in habitat structure and composition resulting from disturbances such as wildfires. Rodents may recolonise burnt areas from individuals that survived the wildfire in ‘internal refuges’ orfrom the surrounding unburnt area (i.e. external colonisation). With the aim of assessing the relative role of both hypotheses on rodent abundance and foraging behaviour after fire, four Mediterranean burnt areas were studied using sampling stations at increasing distances from the perimeter of the burnt area. In the first 18 months after fire, the abundance of wood mice (Apodemus sylvaticus) and seed removal activity were highest near the perimeter. This suggests the weight of external sources (i.e. from unburnt areas) in the recolonisation process is higher than that of internal refuges. Algerian mice (Mus spretus) colonised the burnt areas from external sources. Vegetation cover was the most important variable affecting the relative abundance of rodents in recently burnt areas. After some months of vegetation recovery, rodent individualsthat had dispersed from the unburnt area were likely to take advantage ofsparsely occupied habitat with sufficient resources and, at this time, might use internal refuges. Therefore, understanding recolonisation dynamics is fundamental to anticipate biodiversity patterns and promote adaptive management.
Edges are ecologically important environmental features and have been well researched in agricultural and urban landscapes. However, little work has been conducted in flammable ecosystems where spatially and temporally dynamic fire edges are expected to influence important processes such as recolonization of burnt areas and landscape connectivity. We review the literature on fire, fauna, and edge effects to summarize current knowledge of faunal responses to fire edges and identify knowledge gaps. We then develop a conceptual model to predict faunal responses to fire edges and present an agenda for future research. Faunal abundance at fire edges changes over time, but patterns depend on species traits and resource availability. Responses are also influenced by edge architecture (e.g., size and shape), site and landscape context, and spatial scale. However, data are limited and the influence of fire edges on both local abundance and regional distributions of fauna is largely unknown. In our conceptual model, biophysical properties interact with the fire regime (e.g., patchiness, frequency) to influence edge architecture. Edge architecture and species traits influence edge permeability, which is linked to important processes such as movement, resource selection, and species interactions. Predicting the effect of fire edges on fauna is challenging, but important for biodiversity conservation in flammable landscapes. Our conceptual model combines several drivers of faunal fire responses (biophysical properties, regime attributes, species traits) and will therefore lead to improved predictions. Future research is needed to understand fire as an agent of edge creation; the spatio‐temporal flux of fire edges across landscapes; and the effect of fire edges on faunal movement, resource selection, and biotic interactions. To aid the incorporation of new data into our predictive framework, our model has been designed as a Bayesian Network, a statistical tool capable of analyzing complex environmental relationships, dealing with data gaps, and generating testable hypotheses.
Wildfires play a determining role in the composition and structure of many plant and animal communities. On the other hand, climate change is considered to be a major driver of current and future fire regime changes. Despite increases in drought in many areas of the world, the effects of aridity on post-fire colonization by animals have been rarely addressed. This study aims to analyse how a regional aridity gradient affects post-fire recovery of vegetation, bird species richness and the numbers of four early to middle-successional warbler species associated with the shrub cover. The database contains bird relative abundance and environmental variables from 3072 censuses in 695 transects located in 70 recently burnt areas (1 to 11 years after wildfire) in Catalonia (Spain), which were sampled between 2006 and 2013. Generalized linear mixed models (GLMMs) showed that plant cover was affected by time since fire, aridity and forest management. However, only the highest vegetation height layer (>100 cm) recovered slower in arid areas after fire. Time since fire positively influenced bird species richness and the relative abundance of the four focal species. The post-fire recovery of Melodious (Hippolais polyglotta) and Subalpine warblers (Sylvia cantillans) was hampered by aridity. Although this was not demonstrated for Dartford (S. undata) and Sardinian warblers (S. melanocephala), their occurrence was low in the driest areas during the first three years after fire. Overall, this study suggests that future increases in aridity can affect plant regeneration after fire and slow down the recovery of animal populations that depend on understorey and shrublands. Given the recently highlighted increases in aridity and fire frequency in Mediterranean-climate regions, improved knowledge on how aridity affects ecological succession is especially necessary.
Reserve systems are part of biodiversity conservation planning. However, reserves are rarely assessed for their contribution to population persistence. Here we address knowledge gaps on reserve effectiveness by developing a new approach to model protected area efficacy as a function of habitat suitability and natural disturbance regimes. We demonstrate the utility of the model through a detailed case study of the critically endangered Leadbeater’s possum (Gymnobelideus leadbeateri) in south–eastern Australia. We defined reserve effectiveness for the species to be when there was no more than 5% probability of populations falling to (or below) 500 adult females in 40 generations. A reserve system established specifically for Leadbeater’s possum was found inadequate to ensure population persistence for the next 40 generations, given historical disturbance, habitat decline, and future fires. Simulation modelling of potential areas of reserve suggests that, depending on management risk tolerance, between 30% to 100% of current forest extent within the range of the species may be required to ensure population persistence. This study exemplifies the need to consider the size of reserves prior to their establishment to ensure an adequate reserve design that will be effective against future disturbance for conserving threatened species.
Camera trapping is a widely applied method to study mammalian biodiversity and is still gaining popularity. It can quickly generate large amounts of data which need to be managed in an efficient and transparent way that links data acquisition with analytical tools.
We describe the free and open‐source R package camtrapR , a new toolbox for flexible and efficient management of data generated in camera trap‐based wildlife studies. The package implements a complete workflow for processing camera trapping data. It assists in image organization, species and individual identification, data extraction from images, tabulation and visualization of results and export of data for subsequent analyses. There is no limitation to the number of images stored in this data management system; the system is portable and compatible across operating systems.
The functions provide extensive automation to minimize data entry mistakes and, apart from species and individual identification, require minimal manual user input. Species and individual identification are performed outside the R environment, either via tags assigned in dedicated image management software or by moving images into species directories.
Input for occupancy and (spatial) capture–recapture analyses for density and abundance estimation, for example in the R packages unmarked or secr , is computed in a flexible and reproducible manner. In addition, survey summary reports can be generated, spatial distributions of records can be plotted and exported to gis software, and single‐ and two‐species activity patterns can be visualized.
camtrapR allows for streamlined and flexible camera trap data management and should be most useful to researchers and practitioners who regularly handle large amounts of camera trapping data.
In fire-prone regions, wildfire influences spatial and temporal patterns of landscape heterogeneity. The likely impacts of climate change on the frequency and intensity of wildfire highlights the importance of understanding how fire-induced heterogeneity may affect different components of the biota. Here, we examine the influence of wildfire, as an agent of landscape heterogeneity, on the distribution of arboreal mammals in fire-prone forests in south-eastern Australia. First, we used a stratified design to examine the role of topography, and the relative influence of fire severity and fire history, on the occurrence of arboreal mammals 2-3 years after wildfire. Second, we investigated the influence of landscape context on the occurrence of arboreal mammals at severely burnt sites. Forested gullies supported a higher abundance of arboreal mammals than slopes. Fire severity was the strongest influence, with abundance lower at severely burnt than unburnt sites. The occurrence of mammals at severely burned sites was influenced by landscape context: abundance increased with increasing amount of unburnt and understorey-only burnt forest within a 1 km radius. These results support the hypothesis that unburnt forest and moist gullies can serve as refuges for fauna in the post-fire environment and assist recolonization of severely burned forest. They highlight the importance of spatial heterogeneity created by wildfire and the need to incorporate spatial aspects of fire regimes (e.g., creation and protection of refuges) for fire management in fire-prone landscapes.
Leadbeaters possum was monogamous with a matriarchal pattern of social organisation and life history. A social unit for this species most frequently consists of a breeding pair, one or more generations of offspring and up to 2 additional unrelated adult males. Each group occupies a bark nest in a hollow tree, close to the centre of a 1-2 ha defended territory. The maintenance of population density and spacing appears to be facilitated by inter-female aggression and dispersal of juvenile females. Female offspring disperse at an earlier age (10 months) than males (15 months) and suffer a high mortality due to their exclusion from established colonies. Dispersing male offspring in contrast may be absorbed as non-breeding residents in neighbouring colonies while awaiting mating opportunities. High male survival contributes to a population surplus after favourable years which may lead to reproductive failure in subsequent seasons.-Author
Wildfires in southern California chaparral burn at high intensities and often cover thousands of hectares. Some small mammals survive the fire, while others colonize from scattered unburned islands and from intact vegetation bordering the main fire perimeter. For ten years (2002–2011) we live-trapped two grids and used the number of captures to examine post-fire small mammal use of a narrow 65-m zone straddling the high-contrast edge between burned and unburned chaparral on the perimeter of a high-intensity wildfire. Results indicate that agile kangaroo rats (Dipodomys agilis) were captured more often in open, burned areas than in unburned chaparral. Deer mice (Peromyscus maniculatus) were captured equally in burned and unburned chaparral but did not show an affinity for either habitat or the edge of the burn. Pinyon mice (Peromyscus truei) were captured most often in unburned chaparral throughout the study but were prevalent on the burn edge in years one and four. In the first year post-fire, California mice (Peromyscus californicus) were captured more frequently in unburned than burned chaparral but in years four and five, captures shifted toward the edge and then into the burn areas in year nine. We did not find evidence that any of the four species were dedicated edge specialists in this study. Neither pinyon mice nor California mice appeared to be permanent residents of the burns in the first ten years post-fire. We suggest that future research on post-fire small mammal succession in chaparral would benefit from chronosequence studies that give a more comprehensive, long term picture of succession.
The impact of time since fire after two consecutive wildfires 44 years apart (1939 and 1983) within the same area, and the distance from the fire boundary (<100 m or 500-2000 m), were investigated in relation to the distribution and abundance of arboreal marsupials in 1994. Arboreal marsupials were censused by stagwatching and spotlighting in two relatively young age classes of mountain ash (Eucalyptus regnans) dominated forest in the Central Highlands of Victoria. Five species of arboreal marsupial were detected, but only three were detected in sufficient numbers to determine habitat preferences. Petauroides volans (greater glider) was statistically more abundant in 1939 regrowth forests, while Trichosurus caninus (mountain brushtail possum) showed no significant preference for either age class of forest. All but one record of Gymnobelideus leadbeateri (Leadbeater's possum) came from young forest, though the effect of age-class was not statistically significant. Distance from fire boundary explained little or no variation in mammal distribution or abundance. While the actual number of hollow-bearing trees was similar in both age classes of forest, the long-term lifespan of hollow-bearing trees in more recently burnt forest is predicted to be lower than in unburnt or not recently burnt forest. Post-fire salvage logging following the 1983 wildfires appears to have reduced the number of hollow-bearing trees at sites burnt in 1983.
Unburnt patches within a fire boundary may act as refuges for fauna, facilitating their survival and persistence within fire-prone landscapes. Unburnt patches can arise due to various processes, including topographic variation, fire behaviour, and fuel reduction from recent burning. However, the value of unburnt patches of differing characteristics to the post-fire persistence of faunal communities has rarely been examined. In this study, we examined the relative importance of fire history and severity in predicting the occurrence of birds in a burnt forest landscape. We conducted surveys in mixed eucalypt forest of south-east Australia, 2–3 years after a high intensity, landscape-scale wildfire (>200,000 ha). Sites (n = 91) were selected to encompass fire severity ranging from unburnt patches to stands of crown-burnt forest. Fire history prior to the wildfire was defined as short (<3 years) or long (>20 years) time-since-fire. Unburnt patches of long time-since-fire were important avian refuges, harbouring 20–40% more species, up to 56% more individuals and an assemblage that was distinct from that at all sites burnt by the wildfire, including low severity ground fire. No difference in species richness or composition was detected between sites in unburnt patches of short or long time-since-fire; but bird abundance was ∼20% lower in patches of short time-since-fire. Unburnt and ground-burnt patches of short time-since-fire provided habitat for more species and had distinct assemblages from that of severely burnt sites. For sites severely burnt in the wildfire, there was no difference in avifaunal richness, abundance or composition between those burnt twice in rapid succession and those not burnt for >20 years. Together, these results highlight: (1) the particular importance of unburnt vegetation remaining within fire-affected areas as faunal refuges, and (2) the potential for recent planned burns to contribute to refuge habitat if it avoids severe burning in a subsequent wildfire.
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.
Large quantities of dead wood can be generated by disturbances such as wildfires. Dead trees created by disturbances play many critical ecological roles in forest ecosystems globally. The ability of deadwood to serve its ecological roles is contingent, in part, on the length of time trees remain standing following disturbance. Here, we briefly outline the results of a 10‐year study that aimed to quantify the rate of collapse of trees killed in a major wildfire in the wet ash forests of mainland south‐eastern Australia. We also quantified the factors associated with dead tree collapse. Our analyses revealed that 23% of 417 measured trees collapsed between 2011 and 2021. The most parsimonious model of the factors influencing tree collapse revealed a strong effect of diameter; smaller diameter trees were more likely to collapse over the 10 years of our study than larger diameter trees. In addition, trees in small and large patches were more likely to collapse than trees in contiguous forest (where there had been no logging in the surrounding area). If current rates of tree fall are maintained, then many of trees initially measured will have collapsed by 2030. Such losses of dead trees will have major negative effects on key values of ash‐type forests such as biodiversity conservation.
Many forest species are adapted to long-interval, high-severity fires, but the intervals between severe fires are decreasing with changes in climate, land use, and biological invasions. Although the effects of changing fire regimes on some important recovery processes have previously been considered, the consequences for the dispersal of propagules (plant seeds and fungal spores) in forest communities have not. We characterize three mechanisms by which changing fire regimes disrupt propagule dispersal in mesic temperate, boreal, and high-elevation forests: reduced abundance and altered spatial distributions of propagule source populations, less effective dispersal of propagules by wind, and altered behavior of animal dispersers and propagule predators. We consider how disruptions to propagule dispersal may interact with other factors that are also influenced by fire regime change, potentially increasing risk of forest conversion. Finally, we highlight urgent research topics regarding how dispersal limitation may shape twenty-first century forest recovery after stand-replacing fire.
Fire is a major ecological driver in many Australian ecosystems, and large-scale wildfires can impact on faunal assemblages at a landscape scale. Monitoring the response of the avian community and individual bird species following a 92 039 ha wildfire in the Pilliga Forest, in temperate inland south-eastern Australia, showed an initial decline in species richness and changes in community composition, followed by gradual recovery. Recovery was not complete by the end of the seven-year study. Eighteen species (including Speckled Warbler Chthonicola sagittata and Eastern Yellow Robin Eopsaltria australis) were identified as likely to be fire sensitive and nine species (including Australian Magpie Cracticus tibicen and Red-capped Robin Petroica goodenovii) as likely to respond positively to fire at the time scale of this study. Another 11 species (including Dusky Woodswallow Artamus cyanopterus and Jacky Winter Microeca fascinans) appeared to favour burnt areas close to the fire edge. Guild-level patterns included an overall negative response to fire by insectivores, granivores/frugivores and declining woodland birds and a positive response by predators. The avian community recovered more quickly at burnt sites close to (within 2 km of) the fire edge compared to more remote sites more than 4 km from unburnt habitat, suggesting that proximity to unburnt areas (and therefore fire extent) is likely to be a key consideration in understanding the post-fire recovery of birds.
The midstorey is a critical structural component of many forests globally. Using statistical models, we quantified the influence of two sets of variables on the percentage cover and basal area of two dominant Acacia spp. (Montane Wattle [Acacia frigescens] and Silver Wattle [Acacia dealbata]) in the midstorey of Mountain Ash (Eucalyptus regnans) forests in mainland south‐eastern Australia. Specifically, we focused on the influence of (1) the age of the overstorey eucalypts (corresponding to the time since the last stand‐replacing disturbance), and (2) environmental drivers (aspect, topographic wetness index, slope, elevation). We found evidence for generally non‐linear relationships between stand age and the percentage cover and the basal area of both Silver Wattle and Montane Wattle. Silver Wattle had the highest values for percentage cover, and Montane Wattle the lowest, in stands regenerating from fire in 2009. The basal area of Silver Wattle was highest in stands that regenerated after the 2009 wildfires and after disturbance that occurred between 1960 and 1990s. For Montane Wattle, basal area was lowest in stands that regenerated in 2009 but values did not differ among stands of other ages. Both Acacia species were a midstorey component in old‐growth Mountain Ash forest. No environmental covariates influenced the percentage cover of Montane Wattle or Silver Wattle. However, our model for the basal area of Montane Wattle contained evidence of a positive relationship with topographic wetness. The general paucity of environmental drivers in most of the models we constructed is likely due to the fact that both tree species occur well beyond our study region. Hence, the set of environmental conditions modelled may not be limiting the percentage cover or basal area of these midstorey tree species. Disturbance appears to be the key driver of dynamics of Montane Wattle and Silver Wattle in Mountain Ash forests.
The catastrophic 2009 wildfires in the Mountain Ash (Eucalyptus regnans) forests of the Central Highl&s of Victoria provided an opportunity to gain new insights into the responses to fire by various elements of the biota. Ongoing long-term monitoring at a large number of permanent field sites for up to 25 years prior to the fire, together with 10 years of post-fire monitoring, has provided an unparalleled series of datasets on mammal, bird, & plant responses on burned & unburned sites. The empirical studies briefly summarized in this paper show patterns of steep declines in large old trees & declines in site occupancy by arboreal marsupials & birds. These changes contrast markedly with the responses of the two most common species of small mammals (the Agile Antechinus [Antechinus agilis] & Bush Rat [Rattus fuscipes]), which recovered within two generations after the fire. Declines in arboreal marsupials, birds & large old trees have also occurred on unburned sites, indicating an ecosystem-wide trend. In general, logging had a greater impact than fire on the majority of groups of birds & plants, particularly post-fire salvage logging that occurred in some areas following the 2009 wildfires. Beyond interactions between fire & post-fire (salvage) logging & their effects on forest biota, we have uncovered evidence of other kinds of interactions in Mountain Ash forests. These include interactions between: (1) the severity of fires & logging history, (2) post-fire bird population recovery & long-term climate & short-term weather conditions, & (3) impacts on forest soils. The structure & l&scape composition of the Mountain Ash ecosystem has been radically altered over the last century. This has resulted from the combined impact of several large fires, including the 2009 fires as well as widespread clearfell logging that has been conducted within state forests over the last 50 years. The ecosystem now supports old growth cover that is 1/30th to 1/60th of what it was estimated to have been prior to European settlement. The ongoing decline of key components of the Mountain Ash ecosystem has led to it being classified as Critically Endangered & at high risk of ecosystem collapse. We argue that current forest policy & practices need to better mitigate the effects of fire on this already highly disturbed forest & enhance the possible persistence of species in this ecosystem. Several key strategies are required to do this. First, there is a need to significantly exp& the extent of old growth within the Mountain Ash forest estate. This is because fire severity is diminished in such areas. Spatial contagion across old-growth dominated l&scapes also may be suppressed relative to l&scapes composed primarily of young forest. Allied management strategies include the protection of more mesic parts of Mountain Ash l&scapes as these are less likely to burn or at least burn at high severity. Such enhanced protection should include an exp&ed network of buffers around drainage lines & waterways as these are where fire severity is likely to be lowest & also where old growth elements like large old hollow-bearing trees are more abundant. In addition, all existing living & dead hollow-bearing trees need to be protected by buffers of unlogged forest within wood production forests to promote their st&ing life & better conserve cavity-dependent fauna such as the Critically Endangered Leadbeater’s Possum (Gymnobelideus leadbeateri) & other declining taxa like the Greater Glider (Petauroides volans).
In forests subject to stand-replacing disturbances, early successional stands can provide important habitats for a range of species not typically present in long-undisturbed areas. Compared to old-growth forests, the habitat values of – and key ecological processes in – early successional forests have been less studied, perhaps due to a perception that early successional forests revert to a homogenous “clean slate” following stand-replacing disturbances. In this paper, we draw on 36 years of long-term research in the Mountain Ash (Eucalyptus regnans) and Alpine Ash (Eucalyptus delegatensis) forests of south-eastern Australia, together with examples from elsewhere around the world, to show that not all kinds of early successional forests are created equal. We argue that the ecological values of early successional forests can be profoundly affected by six inter-related factors: (1) The evolutionary context and environmental domain of a given ecosystem. (2) Successional stage and condition of a forest stand prior to disturbance. (3) Disturbance intensity, severity and type (e.g. wildfire versus clearcutting). (4) Post-disturbance conditions including climate and weather. (5) Post-disturbance management (e.g. salvage logging) which can have significant impacts on biological legacies. And, (6) The relative spatial extent and spatial arrangement of early and late successional forest across a landscape. These factors can influence ecological values directly, or through effects on the types, amount and spatial patterns of biological legacies present in early successional forest. We present a conceptual model highlighting the inter-relationships between these factors and illustrate its use through a detailed case study.
Strategies to improve the management of early successional forests include: (1) Identifying the species associated with post-disturbance environments and the reasons why they occur in such environments. (2) Understanding the types, numbers, and spatial patterns of biological legacies that remain after natural disturbance. (3) Identifying critical areas that should be excluded from logging or other human disturbance. (4) Limiting the extent of post-disturbance activities like salvage logging that undermine the ecological values of, and ecosystem processes in, early successional forests. And, (5) Balancing the relative amounts of early successional versus late successional forest in a given landscape or region to ensure that a variety of forest types are present at any given time, and that critical biological legacies are retained. Paradoxically, ensuring that landscapes support extensive areas of late successional forest is critical so that future early successional forests are not devoid of the biological legacies necessary for ecosystem function and recovery.
Wildfire refugia (unburnt patches within large wildfires) are important for the persistence of fire-sensitive species across forested landscapes globally. A key challenge is to identify the factors that determine the distribution of fire refugia across space and time. In particular, determining the relative influence of climatic and landscape factors is important in order to understand likely changes in the distribution of wildfire refugia under future climates. Here, we examine the relative effect of weather (i.e. fire weather, drought severity) and landscape features (i.e. topography, fuel age, vegetation type) on the occurrence of fire refugia across 26 large wildfires in south-eastern Australia. Fire weather and drought severity were the primary drivers of the occurrence of fire refugia, moderating the effect of landscape attributes. Unburnt patches rarely occurred under 'severe' fire weather, irrespective of drought severity, topography, fuels or vegetation community. The influence of drought severity and landscape factors played out most strongly under 'moderate' fire weather. In mesic forests, fire refugia were linked to variables that affect fuel moisture, whereby the occurrence of unburnt patches decreased with increasing drought conditions and were associated with more mesic topographic locations (i.e. gullies, pole-facing aspects) and vegetation communities (i.e. closed-forest). In dry forest, the occurrence of refugia was responsive to fuel age, being associated with recently burnt areas (<5 years since fire). Overall, these results show that increased severity of fire weather and increased drought conditions, both predicted under future climate scenarios, are likely to lead to a reduction of wildfire refugia across forests of southern Australia. Protection of topographic areas able to provide long-term fire refugia will be an important step towards maintaining the ecological integrity of forests under future climate change.
We report spotlight and camera-trap observations of Leadbeater's possum (Gymnobelideus leadbeateri) at six locations up to 15 km east of its described range. Half of our records occurred in fire-affected, mixed-species forest, with a tree species and seral stage composition that differs markedly from its predominant habitat: late-mature forests dominated by Eucalyptus regnans, E. delegatensis and E. nitens.
The severe impacts of the Black Saturday bushfires in 2009 on Leadbeater’s Possum Gymnobelideus leadbeateri populations has escalated the urgency to implement effective conservation measures for this species. This has been reflected in the positions of both the Victorian and Australian Governments, where more actions are being implemented for the species than at any previous time. However, significant debate still surrounds the most effective suite of actions required to conserve the species, and several reports highlight the need to implement stronger protection measures. The following paper provides a short outline of key developments over recent years and the major actions currently underway to conserve Leadbeater’s Possum. Appendix 1 provides a bibliography listing key publications from 2012-2016. © 2016, Field Naturalists Club of Victoria. All rights reserved.
Large old hollow-bearing trees have a wide range of key ecological roles in forest and other ecosystems globally. Patterns and rates of mortality and decay of these trees had profound effects on the size and composition of their populations. Using an 18-year empirical study of large old trees in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, we sought to determine if there are particular patterns of decline that are shared by a proportion of the trees in a tree population. We also sought to identify drivers of decline of these trees by quantifying relationships between the condition state of trees (viz: tree form) and a range of covariates. We found that time, stand age and fire can individually and in combination, strongly affect the decay (and eventual collapse) of large old trees. In particular, we found compelling evidence that patterns of tree decline were markedly different in old growth forest (stands dating from ∼1850) relative to three other younger age classes examined. Trees in older forest decayed less rapidly than trees of equivalent tree form in younger forest. Old growth stands also were characterized by trees in an overall much lower (more intact) form category than the other age classes of forest. A key pattern in our study was the rapid deterioration of large old trees in the youngest aged stands (viz: those regenerating after fires in 1939 and following disturbance between 1960 and 1990). In these forests, a very high proportion of large old trees were either in the most advanced state of tree decay (form 8) or had collapsed (form 9). This is a major concern given that 98.8% of the Mountain Ash forest ecosystem supports forest belonging to these (or even younger) age cohorts. Our investigation highlights the need for forest management to: (1) increase levels of protection for all existing large old hollow-bearing trees, (2) expand the protection of existing regrowth forest so there is the potential to significantly expand the currently very limited areas of remaining old growth forest.
Many species of arboreal marsupials move regularly between den sites in hollow-bearing trees. We show, based on short-term radio-tracking data, that the Critically Endangered Leadbeater's Possum (Gymnobelideus leadbeateri) can move 100 m (and sometimes up to 600 m) between den sites in hollow-bearing trees. These movement data have significant implications for the design of buffers of unlogged forest to protect colonies of Leadbeater's Possum as well as for crude estimates of the species' population size. © 2018 Royal Zoological Society of New South Wales. All rights reserved.
We studied the decay and collapse of trees with hollows in the montane ash forests of the Central Highlands of Victoria, southeastern Australia. We monitored the condition of >1400 trees for varying periods of time between 1983 and 1993 on 181 sites that varied considerably in stand age, tree species composition, slope, aspect, disturbance history, and a wide range of other parameters. The data analyzed in this study were from: (1) 302 trees on 32 sites, each of 3 ha, measured first in 1983 and then again in 1988 and 1993; (2) 1006 trees on 132 3-ha sites surveyed both in 1988 and 1993; and (3) 399 trees, measured in 1990 and again 1993, that occurred within 49 wildlife corridors where the surrounding forest recently had been clearcut. Our results revealed that >40% of the 302 trees first measured during 1983 had collapsed and fallen to the forest floor by 1993. The annual rate of collapse of trees was more rapid between 1988 and 1993 (4.8%) than between 1983 and 1988 (3.6%). Transition matrices constructed for the probability of tree collapse during each of these 5-yr sampling periods did not differ significantly (P < 0.05) between sampling periods or groups of sites.
We used logit regression modeling to estimate the likelihood of collapse of hollow-bearing trees in relation to their physical characteristics and the attributes of the sites on which they occurred. The collapse of trees with hollows was significantly (P < 0.05) influenced by a range of factors, including tree form and diameter as well as the aspect of the site on which they occurred. These parameters were different from those in wildlife corridors, where tree collapse was related to factors such as aspect and the size of the adjacent logged area.
Hollow-bearing trees are keystone structures in many ecosystems worldwide and they play critical habitat roles for a vast array of fauna through providing denning and/or nesting sites. We quantified empirical relationships between the diameter of hollow-bearing trees and probability of occupancy of these trees by cavity-dependent arboreal marsupials in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, south-eastern Australia. We also quantified the effects of other variables such as stand age and elevation on tree occupancy. Finally, we compared the diameter of occupied and unoccupied hollow-bearing trees with non-hollow-bearing trees in 77-year old forest that regenerated after fires in 1939 and which form the dominant age cohort of trees in our study region.
Hollow-bearing trees occupied by arboreal marsupials had a larger diameter than unoccupied hollow-bearing trees. The mean diameter of both occupied and unoccupied hollow-bearing trees was almost three times that of 1939-aged trees that did not contain hollows. Our analyses contained evidence of inter-specific differences in the diameter of hollow-bearing trees occupied by different species of arboreal marsupials. Beyond the influence on occupancy of tree-level factors such as diameter, we also found that the probability of occupancy of a hollow-bearing tree was affected by the age of the surrounding forest and landscape attributes such as elevation. The probability of occupancy of an individual hollow-bearing tree was highest when that tree was located in regrowth forest, most likely because of the scarcity of these critical nesting and denning resources in such stands.
Populations of large hollow-bearing trees, including those typically selected for occupancy by arboreal marsupials, are in rapid decline in Mountain Ash forests. This decline, coupled with the prolonged period until current cohorts of existing younger trees eventually reach an age (and therefore diameter) that are suitable for occupancy by arboreal marsupials, underscores the critical need to protect all existing hollow-bearing trees from practices that can otherwise destroy them, including industrial clearfelling operations. Better protection is important not only in the small remaining areas of old growth Mountain Ash forest but also in regrowth forest where such trees are scarce and have high marginal value as nesting sites, as reflected by high rates of per tree occupancy rates in stands of this age.
Identifying where animals come from during population recovery can help to understand the impacts of disturbance events and regimes on species distributions and genetic diversity. Alternative recovery processes for animal populations affected by fire include external recolonization, nucleated recovery from refuges, or in situ survival and population growth. We used simulations to develop hypotheses about ecological and genetic patterns corresponding to these alternative models. We tested these hypotheses in a study of the recovery of two small mammals, the Australian bush rat and the agile antechinus, after a large (> 50 000 ha), severe wildfire.
The abundance of both species was severely reduced by fire and recovered to near or above pre‐fire levels within two generations, yet we rejected a hypothesis of recovery by external recolonization. While the agile antechinus showed genetic evidence for far greater dispersal capacity than the bush rat, neither species showed gradients in abundance or genetic diversity with distance from unburnt forest during population recovery.
Population recovery was driven by local‐scale processes. However, the mechanisms differed between species, resulting from the spatial impacts of fire on habitat suitability. Agile antechinus populations recovered through population growth from in situ survivors. The bush rat followed a model of nucleated recovery, involving local recolonization from micro‐refuges in topographic drainage lines.
Nucleated recovery by the bush rat was associated with changes in dispersal, and fine‐scale patterns of genetic admixture. We identified increased dispersal by females during recovery, contrasting with male‐biased dispersal in unburnt forest. Such flexibility in dispersal can potentially increase recovery rates compared to expectations based on dispersal behavior within undisturbed populations.
Our study shows how the initial distribution of survivors, determined by fire effects on resource distribution, determines the subsequent scaling of population recovery patterns, and the sensitivity of population distribution and genetic diversity to changing disturbance regimes.
Ecological memory is central to how ecosystems respond to disturbance and is maintained by two types of legacies – information and material. Species life-history traits represent an adaptive response to disturbance and are an information legacy; in contrast, the abiotic and biotic structures (such as seeds or nutrients) produced by single disturbance events are material legacies. Disturbance characteristics that support or maintain these legacies enhance ecological resilience and maintain a “safe operating space” for ecosystem recovery. However, legacies can be lost or diminished as disturbance regimes and environmental conditions change, generating a “resilience debt” that manifests only after the system is disturbed. Strong effects of ecological memory on post-disturbance dynamics imply that contingencies (effects that cannot be predicted with certainty) of individual disturbances, interactions among disturbances, and climate variability combine to affect ecosystem resilience. We illustrate these concepts and introduce a novel ecosystem resilience framework with examples of forest disturbances, primarily from North America. Identifying legacies that support resilience in a particular ecosystem can help scientists and resource managers anticipate when disturbances may trigger abrupt shifts in forest ecosystems, and when forests are likely to be resilient.
Large old trees are keystone structures in numerous ecosystems globally. They play a wide range of critical ecological roles and therefore quantifying the factors influencing their distribution and abundance therefore has significant management implications. Yet, there are few ecosystems worldwide for which quantitative statistical models of the factors affecting large old tree distribution and abundance have been produced. We constructed a suite of such models using cross-sectional data on the occurrence of large old hollow-bearing trees gathered in 2015 on 166 sites, each of 1 ha in size within the montane ash forests of the Central Highlands of Victoria, south-eastern Australia. Our analyses included two broad groups of models, those for: (1) the overall abundance of large old hollow-bearing trees at a site, and (2) the abundance of large old hollow-bearing trees in four different morphological states of decay. These were large old living trees, large old hollow-bearing trees deemed potentially suitable for marsupial gliders, large old hollow-bearing trees deemed potentially suitable for non-gliding marsupial possums, and large old collapsed hollow-bearing trees.
Most of the models we built encompassed a combination of covariates encompassing environmental factors (such as elevation and topographic wetness), human disturbance (e.g. land tenure), and natural disturbance (wildfire). The overall total abundance of large old hollow-bearing trees (irrespective of morphological form) was greatest at unburned sites, within stands of old-growth forest, within reserves, and on wet sites (as reflected by a topographic wetness index). Conversely, sites in young forests and sites subject to moderate or high severity fire supported the highest abundance of collapsed large old hollow-bearing trees.
Our results demonstrate that different sets of environmental factors and attributes reflecting human disturbance, and natural disturbance affect the abundance of different morphological forms of large old hollow-bearing trees. Therefore, different parts of landscapes are most suitable for different kinds of large old hollow-bearing trees. The findings of this study can help direct management toward places where actions to recover populations of large old hollow-bearing trees are needed and/or are most likely to be effective, such as for conserving cavity-dependent animals.
The first edition of this book has established itself as one of the leading references on generalized additive models (GAMs), and the only book on the topic to be introductory in nature with a wealth of practical examples and software implementation. It is self-contained, providing the necessary background in linear models, linear mixed models, and generalized linear models (GLMs), before presenting a balanced treatment of the theory and applications of GAMs and related models. The author bases his approach on a framework of penalized regression splines, and while firmly focused on the practical aspects of GAMs, discussions include fairly full explanations of the theory underlying the methods. Use of R software helps explain the theory and illustrates the practical application of the methodology. Each chapter contains an extensive set of exercises, with solutions in an appendix or in the book’s R data package gamair, to enable use as a course text or for self-study.
Effects of sharp edges induced by timber harvesting and diffuse edges induced by wildfire on the distribution of arboreal marsupials, were investigated by spotlight surveys in the ash forests of the Victorian Central Highlands. Edges were examined between three age-classes of forest (165+, 55-year-old fire regrowth and logging regrowth 5-20 years after loggging), with sites at 200m intervals up to 900m from the edge. The edge itself appeared to have little effect on the distribution and abundance of the arboreal marsupials recorded in this study; the distribution of species appeared related to features of the adjoining forest patches of differing age including their structure, and the distribution of food resources and hollow-bearing trees. Greater Gliders occured in all ageclasses but were most common in old forest with numbers declining across edges and into 55-year-old fire regrowth. This trend was correlated with the distribution of hollow-bearing trees, particularly live hollow-bearing trees. Yellow-bellied Gliders were mainly recorded from old forest. Fewer individuals were recorded in 55-year-old fire regrowth up to 500m from the adjoining old forest edges. Leadbeater's Possum was recorded in all age-classes but was most commonly recorded in young logging regrowth adjacent to old and 55-year-old forest. Mountain Brushtail Possums were more commonly recorded in old forest and 55-year-old fire regrowth than in the young logging regrowth. The proportion of sites occupied by this species increased significantly in the 55-year-old fire regrowth as the distance from the edge with old forest increased. Common Ringtail Possums were only recorded from 55-year-old fire regrowth, where numbers were too low to identify any relationship with distance from the edge of the other age-classes. The implications of these results for silvicultural and landscape planning are discussed.
Ecological disturbance and climate are key drivers of temporal dynamics in the demography and genetic diversity of natural populations. Micro-scale refuges are known to buffer species' persistence against environmental change, but the effects of such refuges on demographic and genetic patterns in response to short-term environmental variation are poorly understood. We quantified demographic and genetic responses of mountain brushtail possums (Trichosurus cunninghami) to rainfall variability (1992-2013) and to a major wildfire. We hypothesized that there would be underlying differences in demographic and genetic processes between an unburnt mesic refuge and a topographically-exposed zone that was burnt in 2009. Fire caused a two-year decrease in survival in the burnt zone, but the population grew after the fire due to immigration, leading to increased expected heterozygosity. We documented a fire-related behavioural shift, where the rate of movement by individuals in the unburnt refuge to the burnt zone decreased after fire. Irrespective of the fire, there were long-term differences in demographic and genetic parameters between the mesic/unburnt refuge and the non-mesic/burnt zone. Survival was high and unaffected by rainfall in the refuge, but lower and rainfall-dependent in the non-mesic zone. Net movement of individuals was directional, from the mesic refuge to the non-mesic zone, suggesting fine-scale source-sink dynamics. There was higher expected heterozygosity (HE ) and temporal genetic stability in the refuge, but lower HE and marked temporal genetic structure in the exposed habitat, consistent with reduced generational overlap caused by elevated mortality and immigration. Thus, fine-scale refuges can mediate the short-term demographic and genetic effects of climate and ecological disturbance. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
The increasing frequency of large, high‐severity fires threatens the survival of old‐growth specialist fauna in fire‐prone forests. Within topographically diverse montane forests, areas that experience less severe or fewer fires compared with those prevailing in the landscape may present unique resource opportunities enabling old‐growth specialist fauna to survive. Statistical landscape models that identify the extent and distribution of potential fire refuges may assist land managers to incorporate these areas into relevant biodiversity conservation strategies.
We used a case study in an Australian wet montane forest to establish how predictive fire simulation models can be interpreted as management tools to identify potential fire refuges. We examined the relationship between the probability of fire refuge occurrence as predicted by an existing fire refuge model and fire severity experienced during a large wildfire. We also examined the extent to which local fire severity was influenced by fire severity in the surrounding landscape. We used a combination of statistical approaches, including generalized linear modeling, variogram analysis, and receiver operating characteristics and area under the curve analysis (ROC AUC).
We found that the amount of unburned habitat and the factors influencing the retention and location of fire refuges varied with fire conditions. Under extreme fire conditions, the distribution of fire refuges was limited to only extremely sheltered, fire‐resistant regions of the landscape. During extreme fire conditions, fire severity patterns were largely determined by stochastic factors that could not be predicted by the model. When fire conditions were moderate, physical landscape properties appeared to mediate fire severity distribution.
Our study demonstrates that land managers can employ predictive landscape fire models to identify the broader climatic and spatial domain within which fire refuges are likely to be present. It is essential that within these envelopes, forest is protected from logging, roads, and other developments so that the ecological processes related to the establishment and subsequent use of fire refuges are maintained.
Most wildlife studies using camera traps have targeted ground-dwelling mammals. Hence, little is known about the effectiveness of camera traps at detecting arboreal species. The objective of this investigation was to test the effectiveness of camera traps at determining site occupancy for a cryptic arboreal marsupial, Leadbeater’s possum (Gymnobelideus leadbeateri). Motion-sensing cameras were installed facing bait stations at a height of 4 m in 15 active G. leadbeateri territories in the Victorian Central Highlands. A pilot study compared the effectiveness of cameras mounted in the standard position to take landscape photographs with that of cameras rotated 90° to take portrait images (so motion-detection bands ran vertically up the tree trunk rather than across the trunk). Cameras in the latter position took 6.5 times more images of the most commonly encountered species (agile antechinus, Antechinus agilis) than those mounted vertically. Thus, cameras were oriented horizontally in all subsequent tests. Cameras were deployed for 1519 trap nights resulting in a total of 4637 trigger events for five arboreal/scansorial mammal species. A total of 1110 trigger events were obtained for G. leadbeateri, and the species was detected at 13 of the 15 sites surveyed. These results confirm that camera traps are an effective technique for detecting some arboreal mammals, including cryptic species such as G. leadbeateri. The method has considerable potential to increase our capacity to undertake targeted surveys for G. leadbeateri over wider areas than is currently feasible, albeit further work is required on the identification of an effective bait to attract G. leadbeateri into the view of camera traps.
Small-mammal dynamics after a wildfire were analysed in Serra Calderona Natural Park (Valencian Community, Spain) over a 11-year period. Burned and unburned sites were surveyed seasonally and the trapping success for Apodemus sylvaticus, Mus spretus and Crocidura russula was analysed. Trapping success in both areas, burned and unburned, is influenced by certain climatic variables, namely minimum, average and maximum temperatures, precipitation and relative humidity. Moreover, in the case of A. sylvaticus, the most captured species along the entire study period, the influence on capture success of each type of site and the capture period were analysed. Twelve years after the wildfire, both areas presented the same qualitative and quantitative small-mammal composition. However, trapping success for A. sylvaticus was greater at the burned sites in 6 out of 11 study years, although with similar annual fluctuations in the two areas. The effect of the considered climatic variables on small-mammal species populations seems to be stronger in the burned area than in the unburned area, which is probably due primarily to the regeneration process after a wildfire.
Although fire is a major form of natural disturbance worldwide, both fire-derived landscape context effects and the impacts of fire severity are poorly known for many species. To address this knowledge gap, we quantified the response of Australian arboreal marsupials to: (1) the spatial effects of fire, (2) fire severity, and (3) fire impacts on the availability of critical nesting resources – hollow-bearing trees. We identified substantial differences among species in response to fire severity and landscape-scale fire. The Sugar Glider (Petaurus breviceps) and the endangered Leadbeater’s Possum (Gymnobelideus leadbeateri) were extremely rare on burned sites irrespective of fire severity. In addition, these two species declined with the amount of burned forest in the surrounding landscape even when their habitat remained unburnt. The Mountain Brushtail Possum (Trichosurus cunninghami) and the Greater Glider (Petauroides volans) both occurred on burned and unburned sites. The Greater Glider responded negatively to fire severity at the site level and also negatively to the amount of forest burned in the surrounding landscape. The abundance of the Mountain Brushtail Possum was lowest on sites subject to moderate severity fire. On unburned sites, the presence and abundance of virtually all species was characterised by a common positive response to the availability of nesting resources in hollow-bearing trees. Our findings underscore the importance of management practices to better protect species that decline after fire. These include conserving areas of unburned forest, particularly those with hollow-bearing trees which are critical nest sites for arboreal marsupials. These recommendations are currently the opposite of existing management practices.
The Department of Natural Resources and Environment of Victoria, Australia, has embarked on a major inventory project, which will provide the first comprehensive, standardized statement of the state's native forest resources. The Statewide Forest Resource Inventory (SFRI) will provide forest managers with resource information for making informed and consistent sustainable yield forecasts, and decisions on forest land-use planning and resource allocation. The SFRI project features detailed stand mapping from aerial photographs combined with model based, variable probability sampling of trees for stem size and defects, tree ring analysis for yield curve development and collection of data on tree hollows and other forest stand information for biodiversity and habitat modelling.