Failing to conserve Leadbeater’s Possum and its Mountain Ash forest habitat

The conservation of the Critically Endangered Leadbeater’s Possum Gymnobelideus leadbeateri in Victoria’s Mountain Ash Eucalyptus regnans forests is one of the most controversial native mammal conservation issues in Australia. Much of the controversy results from long-running conflicts between the demands of the native forest logging industry and associated impacts on Leadbeater’s Possum and its Mountain Ash forest habitat. Here we argue that despite a legislative obligation to protect Leadbeater’s Possum and some limited recent improvements in management, conservation efforts for the species have gone backwards over the past decade. The key problems we identify include that the Victorian Government has: (1) maintained levels of wood production that are too high given the amount of the forest estate that was burned in 2009, (2) failed to substitute clearfell logging practices with more ecologically-sensitive Variable Retention Harvesting Systems, (3) ignored the science (including by its own researchers) on the need for a large protected area for Leadbeater’s Possum, (4) altered key definitions such as those for mature trees and old growth that have substantially weakened the ability to protect the species, and (5) overlooked the array of forest values beyond timber production (such as water and tourism) and which make a greater contribution to the economy. Our analyses suggest that populations of Leadbeater’s Possum are undergoing a substantial decline, as are other hollow-dependent species such as the Greater Glider Petauroides volans. Far more concerted efforts are needed to conserve not only Leadbeater’s Possum but also the Mountain Ash forests in which it presently occurs

The road to oblivion – quantifying pathways in the decline of large old trees

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.The work reported in this paper was funded by the Australian Research Council, The Australian Government (National Environmental Science Program Threatened Species Recovery Hub), and the Government of Victoria

The Leadbeater's Possum Review

This document reviews current science on Leadbeater’s Possum and its montane ash forest habitat in the Central Highlands of Victoria. The report comprises seven chapters on key topics related to the conservation and current management of Leadbeater’s Possum and the forest habitats on which the species depends. Chapter 1 gives a brief history of major events that effect Leadbeater’s Possum and its forest habitat in the Central Highlands of Victoria. Chapter 2 explores work on hollow-bearing trees, as they are the most critical habitat element that will dictate the species’ survival. Chapter 3 reviews some of the recent policies for the management of the species, while Chapters 4 and 5 provide a summary of some of the statistics and other information relating to Leadbeater’s Possum and the forests in which it is found. Chapter 6 explores information about and insights into the Mountain Ash ecosystem and why it is currently classified as Critically Endangered under IUCN Red List of Ecosystems criteria. Chapter 7 reviews many relevant government documents. Chapter 8 contains some general conclusions about the management of Leadbeater’s Possum and the forests in which it occurs. Throughout this report, unless otherwise specified, reference to ANU means the ANU scientists who have conducted research in the Victorian Central Highlands ecosystem over the past 34+ years, or the scientific work that they have produced. We examine the threats to Leadbeater’s Possum as well as critically appraise the effectiveness of management actions and protective measures designed to conserve the species. We examine the Critically Endangered listing of both Leadbeater’s Possum and the Mountain Ash ecosystem in which it lives, and why both are in a parlous state. The review looks back over the history of decisions and other factors that have led us to the current situation, and explores possible futures based on decisions currently being made. Our review relies heavily on the substantial scientific literature on Leadbeater’s Possum and Mountain Ash forest. Long term data and scientifically robust research will play an important role in rigorously assessing many current claims about the status of populations of Leadbeater’s Possum and its habitat and providing clarity on information to guide enhanced decision making. The area of remaining 1939 age forest in the Central Highlands is reaching low levels, and important decisions need to be made about how the forests of this age are managed. The next 5-10 years will be critical for how the Central Highlands ash forests and the species that inhabit them persist (or otherwise) over the next century

Can individual and social patterns of resource use buffer animal populations against resource decline?

Species in many ecosystems are facing declines of key resources. If we are to understand and predict the effects of resource loss on natural populations, we need to understand whether and how the way animals use resources changes under resource decline. We investigated how the abundance of arboreal marsupials varies in response to a critical resource, hollow-bearing trees. Principally, we asked what mechanisms mediate the relationship between resources and abundance? Do animals use a greater or smaller proportion of the remaining resource, and is there a change in cooperative resource use (den sharing), as the availability of hollow trees declines? Analyses of data from 160 sites surveyed from 1997 to 2007 showed that hollow tree availability was positively associated with abundance of the mountain brushtail possum, the agile antechinus and the greater glider. The abundance of Leadbeater's possum was primarily influenced by forest age. Notably, the relationship between abundance and hollow tree availability was significantly less than 1:1 for all species. This was due primarily to a significant increase by all species in the proportional use of hollow-bearing trees where the abundance of this resource was low. The resource-sharing response was weaker and inconsistent among species. Two species, the mountain brushtail possum and the agile antechinus, showed significant but contrasting relationships between the number of animals per occupied tree and hollow tree abundance. The discrepancies between the species can be explained partly by differences in several aspects of the species' biology, including body size, types of hollows used and social behaviour as it relates to hollow use. Our results show that individual and social aspects of resource use are not always static in response to resource availability and support the need to account for dynamic resource use patterns in predictive models of animal distribution and abundance.This research was supported by grants from the Hermon Slade Foundation (HSF 08-4; www.hermonslade.org.au) and the Australian Research Council (www.arc.gov.au), including an APD fellowship to Sam Banks (ARC DP 0984876)

Accounting for biomass carbon stock change due to wildfire in temperate forest landscapes in Australia

Carbon stock change due to forest management and disturbance must be accounted for in UNFCCC national inventory reports and for signatories to the Kyoto Protocol. Impacts of disturbance on greenhouse gas (GHG) inventories are important for many countries with large forest estates prone to wildfires. Our objective was to measure changes in carbon stocks due to short-term combustion and to simulate longer-term carbon stock dynamics resulting from redistribution among biomass components following wildfire. We studied the impacts of a wildfire in 2009 that burnt temperate forest of tall, wet eucalypts in south-eastern Australia. Biomass combusted ranged from 40 to 58 tC ha(-1), which represented 6-7% and 9-14% in low- and high-severity fire, respectively, of the pre-fire total biomass carbon stock. Pre-fire total stock ranged from 400 to 1040 tC ha(-1) depending on forest age and disturbance history. An estimated 3.9 TgC was emitted from the 2009 fire within the forest region, representing 8.5% of total biomass carbon stock across the landscape. Carbon losses from combustion were large over hours to days during the wildfire, but from an ecosystem dynamics perspective, the proportion of total carbon stock combusted was relatively small. Furthermore, more than half the stock losses from combustion were derived from biomass components with short lifetimes. Most biomass remained on-site, although redistributed from living to dead components. Decomposition of these components and new regeneration constituted the greatest changes in carbon stocks over ensuing decades. A critical issue for carbon accounting policy arises because the timeframes of ecological processes of carbon stock change are longer than the periods for reporting GHG inventories for national emissions reductions targets. Carbon accounts should be comprehensive of all stock changes, but reporting against targets should be based on human-induced changes in carbon stocks to incentivise mitigation activities.The funder provided support in the form of salaries for the authors [HK, SO], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript

Where do animals come from during post-fire population recovery? Implications for ecological and genetic patterns in post-fire landscapes

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.Th is research was funded by an Australian Research Council Future Fellowship to Sam Banks (FT130100043)

Complex responses of birds to landscape-level fire extent, fire severity and environmental drivers

Aim: To quantify bird responses to a large unplanned fire, taking into consideration landscape-level fire severity and extent, pre-fire site detection frequency and environmental gradients. Location: South-eastern Australia. Methods: A major wildfire in 2009 coincided with a long-term study of birds and provided a rare opportunity to quantify bird responses to wildfire. Using hierarchical Bayesian analysis, we modelled bird species richness and the detection frequency of individual species in response to a suite of explanatory variables, including (1) landscape-level fire severity and extent (2) pre-fire detection frequency, (3) site-level vegetation density and (4) environmental variables (e.g. elevation and topography). Results: Landscape-level fire severity had strong effects on bird species richness and the detection frequency of the majority of bird species. These effects varied markedly between species; most responded negatively to amount of severely burned forest in the landscape, one negatively to the amount of moderately burned forest and one responded negatively to the total area of burned forest. Only one species - the Flame Robin - responded positively to the amount of burned forest. Relationships with landscape-scale fire extent changed over time for one species - the Brown Thornbill - with initially depressed rates of detection recovering after just 2 years. The majority of species were significantly more likely to be detected in burned areas if they have been recorded there prior to the fire. Main conclusions: Birds responded strongly to the severity and spatial extent of fire. They also exhibited strong site fidelity even after severe wildfire which causes profound changes in vegetation cover - a response likely influenced by environmental features such as elevation and topography

Relationships between tree size and occupancy by cavity-dependent arboreal marsupials

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

An empirical assessment and comparison of species-based and habitat-based surrogates: a case study of forest vertebrates and large old trees

A holy grail of conservation is to find simple but reliable measures of environmental change to guide management. For example, particular species or particular habitat attributes are often used as proxies for the abundance or diversity of a subset of other taxa. However, the efficacy of such kinds of species-based surrogates and habitat-based surrogates is rarely assessed, nor are different kinds of surrogates compared in terms of their relative effectiveness. We use 30-year datasets on arboreal marsupials and vegetation structure to quantify the effectiveness of: (1) the abundance of a particular species of arboreal marsupial as a species-based surrogate for other arboreal marsupial taxa, (2) hollow-bearing tree abundance as a habitat-based surrogate for arboreal marsupial abundance, and (3) a combination of species- and habitat-based surrogates. We also quantify the robustness of species-based and habitat-based surrogates over time. We then use the same approach to model overall species richness of arboreal marsupials. We show that a species-based surrogate can appear to be a valid surrogate until a habitat-based surrogate is co-examined, after which the effectiveness of the former is lost. The addition of a species-based surrogate to a habitat-based surrogate made little difference in explaining arboreal marsupial abundance, but altered the co-occurrence relationship between species. Hence, there was limited value in simultaneously using a combination of kinds of surrogates. The habitat-based surrogate also generally performed significantly better and was easier and less costly to gather than the species-based surrogate. We found that over 30 years of study, the relationships which underpinned the habitat-based surrogate generally remained positive but variable over time. Our work highlights why it is important to compare the effectiveness of different broad classes of surrogates and identify situations when either species- or habitat-based surrogates are likely to be superior.This study has been funded by the Australian Research Council, Parks Victoria, the Department of Sustainability and Environment (and its predecessor departments), Melbourne Water, the Earthwatch Institute, the Thomas Foundation and Lindenmayer’s personal funds

Empirical relationships between tree fall and landscape-level amounts of logging and fire

Large old trees are critically important keystone structures in forest ecosystems globally. Populations of these trees are also in rapid decline in many forest ecosystems, making it important to quantify the factors that influence their dynamics at different spatial scales. Large old trees often occur in forest landscapes also subject to fire and logging. However, the effects on the risk of collapse of large old trees of the amount of logging and fire in the surrounding landscape are not well understood. Using an 18-year study in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, we quantify relationships between the probability of collapse of large old hollow-bearing trees at a site and the amount of logging and the amount of fire in the surrounding landscape. We found the probability of collapse increased with an increasing amount of logged forest in the surrounding landscape. It also increased with a greater amount of burned area in the surrounding landscape, particularly for trees in highly advanced stages of decay. The most likely explanation for elevated tree fall with an increasing amount of logged or burned areas in the surrounding landscape is change in wind movement patterns associated with cutblocks or burned areas. Previous studies show that large old hollow-bearing trees are already at high risk of collapse in our study area. New analyses presented here indicate that additional logging operations in the surrounding landscape will further elevate that risk. Current logging prescriptions require the protection of large old hollow-bearing trees on cutblocks. We suggest that efforts to reduce the probability of collapse of large old hollow-bearing trees on unlogged sites will demand careful landscape planning to limit the amount of timber harvesting in the surrounding landscape.This work was supported by an Australian Research Council Discovery Grant DP1097170 (DBL) http://www.arc.gov.au/; the Victorian Government Department of Environment, land, water and Planning (DBL) https://www2.delwp.vic.gov.au/; Parks Victoria (DBL) http://parkweb.vic.gov.au/ Long Term Ecological Research Network (DBL) http://www.ltern.org.au/; and National Environmental Science Programme Threatened Species Recovery Hub (DBL) http://www.nespthreatenedspecies.edu.au/