Mountain Ash Forests Research Articles

The importance of managing and conserving large old trees: a case study from Victorian Mountain Ash forests

Large old trees are critical structures in the Mountain Ash forests of the Central Highlands of Victoria. They perform many critical ecological and other roles. Populations of these trees are also in serious decline. A range of key management strategies is needed to arrest the decline of existing populations of large old trees and instigate population recovery. In particular all existing large old trees need to be properly protected with adequate buffers of uncut forest. In addition, all stands of old-growth forest, irrespective of their size, need to be protected to ensure they are not logged. The size of the old-growth estate also must be expanded so that it encompasses at least 30%‒50% of the distribution of Mountain Ash. Finally, the recruitment of new cohorts of large old trees is critically important to replace existing trees when they are lost. To achieve this, large areas of existing regrowth forest that regenerated after the 1939 fires need to be excluded from logging and grown through to an old-growth stage. Implementation of altered management in Mountain Ash forests is urgent, as delays in policies will exacerbate the decline of this significant population of large old trees in south-eastern Australia.

The use of topographic fire refuges by the greater glider (Petauroides volans) and the mountain brushtail possum (Trichosurus cunninghami) following a landscape-scale fire

We examined the abundance of arboreal marsupials in topographic fire refuges after a major fire in a stand-replacing crown-fire forest ecosystem. We surveyed the abundance of arboreal marsupials across 48 sites in rainforest gullies burnt to differing extents by the 2009 fires in the mountain ash (Eucalyptus regnans) forests of the Victorian Central Highlands, Australia. The greater glider (Petauroides volans) was less abundant within the extent of the 2009 fire. The mountain brushtail possum (Trichosurus cunninghami) was more abundant within the extent of the 2009 fire, particularly within unburnt peninsulas protruding into burnt areas from unburnt edges. Our results indicate that fire refuges may facilitate the persistence of some species within extensively burnt landscapes. Additional work should seek to clarify this finding and identify the demographic mechanisms underlying this response.

Single large versus several small: The SLOSS debate in the context of bird responses to a variable retention logging experiment

The Variable Retention Harvest System (VRHS) is a silvicultural system designed to reduce logging impacts and enhance biodiversity conservation. VRHS has been widely applied worldwide but several important questions remain about its effectiveness for biodiversity conservation. A key issue is whether dispersed or aggregated retention is more effective for conservation, and hence what size of retained patches of forest should be maintained within logged areas. Many studies have indicated that increasing the amount of the original stand retained during harvesting increases the amount of biodiversity conserved. But in a form of the SLOSS (single large or several small areas for conservation) debate, a critical question is: does one large retained island better conserve forest biota than several small islands of the same aggregated area? We addressed this question in an experiment in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, south-eastern Australia. The experiment comprised seven blocks, each with four treatments – an unlogged control, a conventional 15–40ha clearfelled area, a 15–40ha harvest unit with a single 1.5ha retained “island”, and a 15–40ha harvest unit with three 0.5ha islands. A subset of the treatment plots and harvest units in our experiment were burned in a major wildfire in 2009. Given this, a subsequent further question we posed was: are there additional effects on birds resulting from logging operations that were followed by wildfires.We identified a significant gradient in species richness across treatments with lowest values in conventional clearfelled areas and highest values in unlogged controls. Unexpectedly, we identified no significant island size effects on bird species richness. We found no individual species that were significantly more likely to occur in a single large island than several small islands. Nonmetric multidimensional scaling revealed significant differences in the composition of the bird community between treatments, consistent with our findings for some of the more common species of birds. Several species were significantly less likely to be recorded in clearfelled areas, although the Flame Robin was more likely to be recorded in them. When we removed clearfelled areas from our analyses, some species were significantly less likely to occur in retained islands than unlogged controls. The application of VRHS did not appear to mediate bird responses to wildfire relative to effects for birds observed in clearfelled harvest units that were subsequently burned in 2009.Our results suggest that VRHS has positive effects on bird biota in Mountain Ash forests. However, this study found no advantage of setting aside a single large island versus several small islands within a given harvest unit for bird species richness nor the occurrence of individual bird species.

A succession of theories: purging redundancy from disturbance theory.

The topics of succession and post-disturbance ecosystem recovery have a long and convoluted history. There is extensive redundancy within this body of theory, which has resulted in confusion, and the links among theories have not been adequately drawn. This review aims to distil the unique ideas from the array of theory related to ecosystem change in response to disturbance. This will help to reduce redundancy, and improve communication and understanding between researchers. We first outline the broad range of concepts that have developed over the past century to describe community change in response to disturbance. The body of work spans overlapping succession concepts presented by Clements in 1916, Egler in 1954, and Connell and Slatyer in 1977. Other theories describing community change include state and transition models, biological legacy theory, and the application of functional traits to predict responses to disturbance. Second, we identify areas of overlap of these theories, in addition to highlighting the conceptual and taxonomic limitations of each. In aligning each of these theories with one another, the limited scope and relative inflexibility of some theories becomes apparent, and redundancy becomes explicit. We identify a set of unique concepts to describe the range of mechanisms driving ecosystem responses to disturbance. We present a schematic model of our proposed synthesis which brings together the range of unique mechanisms that were identified in our review. The model describes five main mechanisms of transition away from a post-disturbance community: (i) pulse events with rapid state shifts; (ii) stochastic community drift; (iii) facilitation; (iv) competition; and (v) the influence of the initial composition of a post-disturbance community. In addition, stabilising processes such as biological legacies, inhibition or continuing disturbance may prevent a transition between community types. Integrating these six mechanisms with the functional trait approach is likely to improve the predictive capacity of disturbance theory. Finally, we complement our discussion of theory with a case study which emphasises that many post-disturbance theories apply simultaneously to the same ecosystem. Using the well-studied mountain ash (Eucalyptus regnans) forests of south-eastern Australia, we illustrate phenomena that align with six of the theories described in our model of rationalised disturbance theory. We encourage further work to improve our schematic model, increase coverage of disturbance-related theory, and to show how the model may link to, or integrate with, other domains of ecological theory.

Ecosystem assessment of mountain ash forest in the Central Highlands of Victoria, south‐eastern Australia

AbstractWe applied an ecosystem risk assessment to the mountain ash forest ecosystem of the Central Highlands of Victoria (hereafter ‘mountain ash forest’), south‐eastern Australia, using the IUCN Red List of Ecosystems criteria. Using this methodology, we quantified: (i) key aspects of the ecosystem's historical, current and future decline in spatial distribution; (ii) the extent of occurrence and area of occupancy for the mountain ash ecosystem; and (iii) the decline in key abiotic and biotic processes and features for historical, current and future time periods. We developed a probabilistic model of tree growth stages to estimate the risk of ecosystem collapse within 50 to 100 years in the mountain ash forest. There was uncertainty in our estimates of risk under the various IUCN criteria, with two sub‐criteria being categorized as ‘Data Deficient’. Our overall ranking of risk of collapse for the ecosystem was Critically Endangered. We are confident that this risk category is appropriate because all 39 scenarios modelled indicated a ≥92% chance of ecosystem collapse by 2067. Our findings highlight the important need for timely policy reform to facilitate improved management of the mountain ash ecosystem in Victoria. In particular, there needs to be greater protection of remaining areas of unburned forest, and restoration activities in parts of the forest estate. Implementation of these strategies will require a significant reduction in logging pressure on the mountain ash ecosystem.

Nonlinear Effects of Stand Age on Fire Severity

AbstractWe quantify the relationship between forest stand age and fire severity using a detailed case study of Mountain Ash (Eucalyptus regnans Muell) forest burned in south‐eastern Australia in 2009. We focused on two important areas of Mountain Ash forest that feature a range of growth stages and disturbance histories. Using probit regression analysis, we identified a strong relationship between the age of a Mountain Ash forest and the severity of damage that the forest sustained from the fires under extreme weather conditions. Stands of Mountain Ash trees between the ages of 7 to 36 years mostly sustained canopy consumption and scorching, which are impacts resulting from high‐severity fire. High‐severity fire leading to canopy consumption almost never occurred in young stands (<7 years) and also was infrequent in older (>40 years) stands of Mountain Ash. We discuss the significant forest conservation and management implications of these results for Mountain Ash forests as well as other similar biomes, where high‐severity fire is a common form of disturbance.

Silvicultural recovery in ash forests following three recent large bushfires in Victoria

SummaryThe contrasting regeneration outcomes of alpine ash (Eucalyptus delegatensis) and mountain ash (E. regnans) forests (collectively called ash) after the extensive and severe 2003, 2006/07 and 2009 bushfires in Victoria demonstrate the complexity of factors that influence the establishment of ash regeneration after bushfire. About 189 000 ha of ash forest was killed or severely damaged by the three bushfires, which burnt a land area totalling over 2.6 million ha. Silvicultural recovery work included aerial sowing of about 7100 ha of fire-killed regrowth in state forests with about 6400 kg of seed. This regrowth was less than 15–20 years of age and thus too immature to bear effective quantities of seed to achieve natural self-regeneration.This article includes a brief description of ash regeneration silviculture, a summary of relevant statistics for each of the three fires under consideration and the silvicultural recovery programs. Aspects of the recovery programs for the fires, including strategic seed-crop assessments, seedbed assessments, seed collection and management and aerial sowing operations are described, and their results are provided and discussed. The concept of ‘ecological stocking’, where regeneration levels are less than those required for commercial timber production, is also discussed.The natural seedling stocking levels resulting from the 2003 bushfires, which affected mostly alpine ash forests, were generally very satisfactory in stands of seed-bearing age. In contrast, after the bushfires of 2006/07, both natural and artificially sown eucalypt regeneration levels were often below commercial forestry standards. Natural stocking levels after the 2009 fires were again very satisfactory.

The long term effects of thinning treatments on vegetation structure and water yield

Forest thinning has the potential to be used as a water supply augmentation strategy through the reduction of sapwood and leaf areas that also decreases stand evapotranspiration. This study investigated the long term effects of a range of thinning treatments (patch-cutting, uniform thinning, strip-thinning, understorey removal) on the vegetation structure and water yield of mountain ash (Eucalyptus regnans) forests in south eastern Australia. The paired catchment method and Light Detection and Ranging (LiDAR) data were utilised to assess the post-thinning changes in water yield and vegetation structure respectively. The first post-treatment phase started at the end of the treatments in the late 1970s/early 1980s until the suspension of measurements in 1997, the second post-treatment phase started when the measurements resumed in 2007/2008 until a wildfire in February 2008. Up to 36% increase in annual water yield was detected during the first post-treatment phase. Strip-thinning produced the largest cumulative increase in water yield (up to 1813mm), followed by uniform thinning and patch-cutting. The magnitude of the treatment effect appeared to be amplified during a very wet/dry period, which may be due to post-thinning changes in the runoff generation processes. During the second post-treatment phase, a trend of decreased water yield was detected at several treated catchments. Canopy height profiles (CHPs) and mean effective leaf area index (LAI) that were derived from LiDAR data, along with recent forest inventory data, indicated a recovery of vegetation cover. This may partially explain the decrease in water yield. Meanwhile, the decade-long drought (1997–2008) that coincided with this period of decreased water yield might have exacerbated its magnitude. Thinning may not be a net water gain over the long term if the recent trend of decreasing water yield continues.

Hydrological response to wildfire, integrated logging and dry mixed species eucalypt forest regeneration: The Yambulla experiment

Eucalypts are commonly planted hardwoods worldwide and Eucalyptus dominated forests naturally grow in the headwaters of many Australian water supply catchments. The hydrological effects of disturbances have been extensively reported for one species, E. regnans (Mountain Ash). The typical response to disturbance is unusual in that following an initial increase, with heavy seed dispersal and rapid regeneration, streamflow from these forests is greatly reduced. In New South Wales (NSW), native forests are dominated by different Eucalyptus species that typically grow in mixed-species and mixed-age stands that regenerate less vigorously. In this study the long term streamflow records from the six Yambulla catchments in southeastern NSW were analysed to assess the relative effects of wildfires, integrated logging operations and subsequent mixed species eucalypt forest regeneration on catchment hydrology.In all five treated catchments an increase in total streamflow, baseflow and stormflow was detected following the 1979 wildfire and/or integrated logging activities that occurred at various intervals. A subsequent reduction of streamflow to below that of a mature stand was not detected in three of the catchments but was detected in the two that had been subjected to integrated logging followed by a wildfire, and a wildfire followed by salvage logging, respectively. The reduction, however, was minor and short-lived in each case meaning that overall there was a cumulative increase in streamflow in the post-disturbance period. These results contribute to a growing body of evidence indicating that catchment-scale hydrological responses to disturbance of mixed species eucalypt forests do not follow the unusual response often reported in wet Mountain Ash forests. This has important implications for the modelling and management of mixed species eucalypt hydrology.

Adapting Urban Water Systems to a Changing Climate: Lessons from the Millennium Drought in Southeast Australia

Feature pubs.acs.org/est Adapting Urban Water Systems to a Changing Climate: Lessons from the Millennium Drought in Southeast Australia Stanley B. Grant,* ,†,‡ Tim D. Fletcher, ⊥ David Feldman, § Jean-Daniel Saphores, †,§ Perran L. M. Cook, # Mike Stewardson, ‡ Kathleen Low, † Kristal Burry, ∇ and Andrew J. Hamilton ∥ Department of Civil and Environmental Engineering, E4130 Engineering Gateway, University of California, Irvine, Irvine, California 92697-2175, United States Department of Infrastructure Engineering, Melbourne School of Engineering, Engineering Block D, The University of Melbourne, Parkville 3010, Victoria, Australia Department of Planning, Policy, and Design, 300G Social Ecology I, University of California, Irvine, Irvine, California 92697-7075, United States Department of Agriculture and Food Systems, The University of Melbourne, 940 Dookie−Nalinga Road, Dookie College, Victoria 3647, Australia Melbourne School of Land and Environment, The University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Victoria 3121, Australia Water Studies Centre, School of Chemistry, Monash University, Victoria 3800, Australia Melbourne School of Land and Environment, The University of Melbourne, Parkville Campus, 207 Bouverie Street, Victoria 3052, Australia the way Melburnians source and use their water resources and discuss what these changes may portend for other large cities in water-scarce and climate-change-vulnerable regions of the world, in particular, the Southwest region of the United States. MELBOURNE’S WATER SUPPLY Melbourne sources most of its water from protected stream catchments located in uninhabited mountain ash (Eucalyptus regnans) forests to the north and northeast of the city (Figure 1). Runoff from these protected catchments flows by gravity into ten harvesting reservoirs and, from there, through a network of aqueducts and pipelines to storage reservoirs where it is distributed, after minimal treatment, to local service reservoirs. Since the first harvesting reservoir was built in the mid-1800s, Melbourne’s protected catchments have provided the city with a safe, low-energy, and mostly reliable source of high quality drinking water. However, they have also left the city vulnerable to water shortages during periods of very low precipitation. 5 To buffer against water shortages, Melbourne recently invested in various water supply augmentation schemes, including an interbasin transfer pipeline (the North−South or Sugarloaf Pipeline) and the largest desalination plant in the Southern Hemisphere (the Wonthaggi Desalination Plant) (Figure 1). These two projects were built at a capital cost of approximately AU$700 million 6 and AU$6 billion, 7 respec- tively, and can deliver annually up to 75 and 150 GL of water to Melbourne; combined, that equates to about 40% of the city’s present day municipal water demand. However, since their completion in 2010 (Sugarloaf Pipeline) and 2012 (Wonthaggi Desalination Plant), neither A LONG HISTORY OF DROUGHT IN MELBOURNE Australia is the world’s driest inhabited continent, and its population is one of the most urban. As of 2010, 89% of Australia’s 21 million inhabitants lived in urban areas. 1 Finding adequate water resources to sustain Australia’s cities is an ongoing challenge. 2 Nowhere is that more apparent than in Melbourne, a coastal city of approximately 4 million people located on the country’s southeastern coast. Over its 166-year history, Melbourne has experienced eight major droughts. The most recent one, known as the Millennium Drought, started in 1997 and lasted more than a decade. By 2009, below-average precipitation and above-average temperatures drained the city’s drinking-water reservoirs and stoked bush fires, including the “Black Saturday” fire that damaged 30% of the city’s water supply catchment and claimed 173 lives. 3 The Millennium Drought also altered public perceptions about global climate change, water conservation, and water-use behaviors, and energized city managers and politicians to adopt a wide range of approaches for augmenting water supplies and conserving water resources, although the contribution of climate change to the Millennium drought, while plausible, remains unproven. 4 In this paper, we explore how the Millennium Drought changed © 2013 American Chemical Society Special Issue: Design Options for More Sustainable Urban Water Environment Published: May 3, 2013 dx.doi.org/10.1021/es400618z | Environ. Sci. Technol. 2013, 47, 10727−10734

Bryophyte persistence following major fire in eucalypt forest of southern Australia

The significance of variation in fire severity is not well understood for bryophyte species richness and composition. This is despite fire being a major factor in determining bryophyte richness and composition in temperate forests. We documented the species richness of mosses and liverworts in 42 sites of Mountain Ash (Eucalyptus regnans) forest in eastern Australia. We compared two age classes: long unburned stands and 72year old stands following a major fire in February 2009. Within these two age classes, we surveyed sites of contrasting fire severity: (1) unburned, (2) subject to moderate severity fire (intact canopy) and (3) subject to high severity fire (burned canopy). At each site, we surveyed bryophytes in 10m×100m transects, which was large enough to include a variety of microhabitats. Roughly 60% of the variation in species richness (r2=0.61, p<0.001) and composition (R=0.57, p<0.001) was explained by fire severity. High severity fire removed all bryophytes and only pioneer species were present 2years later. In contrast, the moderate severity fire sites were often species rich because they harboured pioneer bryophytes and species associated with long unburned forest. A key finding was the importance of small unburned patches that contained understorey trees and logs for boosting bryophyte richness. Practices such as salvage logging that remove biological legacies are inconsistent with the conservation of bryophyte diversity in this landscape.

Principles and practices for biodiversity conservation and restoration forestry: a 30 year case study on the Victorian montane ash forests and the critically endangered Leadbeater's Possum

We present a detailed case study of conservation and restoration of the Australian arboreal marsupial Leadbeater's Possum (Gymnobelideus leadbeateri) and its Mountain Ash forest habitat to illustrate the important intersection between forest restoration principles and the general principles for forest biodiversity conservation. Mountain Ash forests have been extensively modified through a century of intensive logging, recurrent wildfires and post-fire salvage logging. These disturbances have led to a reduction in old growth forest to 1/30th-1/60th of the extent of historical levels, a rapid collapse followed by a prolonged (≯30-year) shortage of populations of hollow-bearing trees throughout the Mountain Ash forests (which are critical habitat elements for many species of cavity-dependent vertebrates), and an increased risk of re-burning of landscapes dominated by young, regrowth forest. The consequences of the severe decline and consequent ‘temporary extinction’ of large old trees will be the potential g...

Interacting Factors Driving a Major Loss of Large Trees with Cavities in a Forest Ecosystem

Large trees with cavities provide critical ecological functions in forests worldwide, including vital nesting and denning resources for many species. However, many ecosystems are experiencing increasingly rapid loss of large trees or a failure to recruit new large trees or both. We quantify this problem in a globally iconic ecosystem in southeastern Australia – forests dominated by the world's tallest angiosperms, Mountain Ash (Eucalyptus regnans). Tree, stand and landscape-level factors influencing the death and collapse of large living cavity trees and the decay and collapse of dead trees with cavities are documented using a suite of long-term datasets gathered between 1983 and 2011. The historical rate of tree mortality on unburned sites between 1997 and 2011 was >14% with a mortality spike in the driest period (2006–2009). Following a major wildfire in 2009, 79% of large living trees with cavities died and 57–100% of large dead trees were destroyed on burned sites. Repeated measurements between 1997 and 2011 revealed no recruitment of any new large trees with cavities on any of our unburned or burned sites. Transition probability matrices of large trees with cavities through increasingly decayed condition states projects a severe shortage of large trees with cavities by 2039 that will continue until at least 2067. This large cavity tree crisis in Mountain Ash forests is a product of: (1) the prolonged time required (>120 years) for initiation of cavities; and (2) repeated past wildfires and widespread logging operations. These latter factors have resulted in all landscapes being dominated by stands ≤72 years and just 1.16% of forest being unburned and unlogged. We discuss how the features that make Mountain Ash forests vulnerable to a decline in large tree abundance are shared with many forest types worldwide.

Differences in water use between mature and post-fire regrowth stands of subalpine Eucalyptus delegatensis R. Baker

We estimated plot level water use from sap flux measurements over a 9-month period, in post-fire regrowth and mature plots of Eucalyptus delegatensis R. Baker (Alpine ash) in high elevation catchments near Falls Creek, Victoria, Australia, seven years after a major stand-replacing bushfire. Water use was more than double (460±100mmyear−1 more) in regrowth as compared to mature plots, whereas sap flux was similar between age classes. This difference in water use reflected 72% greater sapwood area index and 35% greater leaf area index in regrowth than in mature plots. A small part of the difference in water use can be attributed to nocturnal transpiration, which was greater in regrowth than in mature plots (10.3±0.8% vs 7.3±0.8% of diel totals). As evaporative demand was 41% greater in mature than in regrowth plots, these data suggest mean transpiration rate and stomatal conductance per unit leaf area were approximately 1.6 and 2.3 times greater, respectively, in the regrowth. However, mid-day leaf water potential and photosynthetic capacity were similar in both age classes. Evaporative demand was the primary environmental driver of water use in all cases, whereas soil moisture was not a strong driver of either water use or canopy conductance (estimated as sap flux/evaporative demand). Together, our results suggest (a) stand water use rapidly recovers after fire in these high elevation forests and quickly surpasses rates in mature stands, confirming projections by Kuczera (1987) for lower-elevation Mountain Ash (E. regnans) forests and highlighting the potential impact of tree water use on water yield in the first decade of forest regeneration after fires, and (b) stomatal conductance and sapwood area/leaf area ratio are both less in tall, older Alpine ash trees, whereas leaf water status and photosynthetic capacity appear to be sustained – consistent with predictions from optimisation theory but not Pipe-Model Theory.

Societal challenges in understanding and responding to regime shifts in forest landscapes

Many natural landscapes have undergone dramatic permanent alterations as a result of human activities, including conversion to cultural landscapes; such changes are readily observed and understood. However, extensive ecological change can also occur in regional landscapes that are maintained in a seminatural state, changes that go largely unrecognized because the regional landscape retains an approximation of its dominant physiognomic cover, such as forest or grassland. In PNAS, Lindenmayer et al. (1) describe the concept of regime shifts in forest landscapes that represent landscape traps in that “entire landscapes are shifted into a state in which major functional and ecological attributes are compromised [and] lead to feedback processes that either maintain an ecosystem in a compromised state or push it into a further regime shift in which an entirely new type of vegetation cover develops.” Such state changes can result in dramatic reductions in functionality (e.g., carbon sequestration, water yields) and biodiversity, as with their primary example of mountain ash forests (Eucalyptus regnans) in southeastern Australia.

Newly discovered landscape traps produce regime shifts in wet forests

We describe the "landscape trap" concept, whereby entire landscapes are shifted into, and then maintained (trapped) in, a highly compromised structural and functional state as the result of multiple temporal and spatial feedbacks between human and natural disturbance regimes. The landscape trap concept builds on ideas like stable alternative states and other relevant concepts, but it substantively expands the conceptual thinking in a number of unique ways. In this paper, we (i) review the literature to develop the concept of landscape traps, including their general features; (ii) provide a case study as an example of a landscape trap from the mountain ash (Eucalyptus regnans) forests of southeastern Australia; (iii) suggest how landscape traps can be detected before they are irrevocably established; and (iv) present evidence of the generality of landscape traps in different ecosystems worldwide.

Extracting LiDAR indices to characterise multilayered forest structure using mixture distribution functions

Discrete Light Detection and Ranging (LiDAR) data is used to stratify a multilayered eucalyptus forest and characterise the structure of the vertical profile. We present a methodology that may prove useful for a very broad range of forest management applications, particularly for timber inventory evaluation and forest growth modelling. In this study, we use LiDAR data to stratify a multilayered eucalyptus forest and characterise the structure of specific vegetation layers for forest hydrology research, as vegetation dynamics influence a catchment's streamflow yield. A forest stand's crown height, density, depth, and closure, influence aerodynamic properties of the forest structure and the amount of transpiring leaf area, which in turn determine evapotranspiration rates. We present a methodology that produces canopy profile indices of understorey and overstorey vegetation using mixture models with a wide range of theoretical distribution functions. Mixture models provide a mechanism to summarise complex canopy attributes into a short list of parameters that can be empirically analysed against stand characteristics. Few studies have explored theoretical distribution functions to represent the vertical profile of vegetation structure in LiDAR data. All prior studies have focused on a Weibull distribution function, which is unimodal. In a complex native forest ecosystem, the form of the distribution of LiDAR points may be highly variable between forest types and age classes. We compared 44 probability distributions within a two component mixture model to determine the most suitable bimodal distributions for representing LiDAR density estimates of Mountain Ash forests in south-eastern Australia. An elimination procedure identified eleven candidate distributions for representing the eucalyptus component of the mixture model. We demonstrate the methodology on a sample of plots to predict overstorey stand volumes and basal area, and understorey basal area of 18-, 37-, and 70-year old Mountain Ash forest with variable density classes. The 70-year old forest has been subjected to a range of treatments including: thinning of the eucalyptus layer with two distinct retention rates, removal of the understorey, and clear felling of patches that have 37 year old regenerating forest. We demonstrate that the methodology has clear potential, as observed versus predicted values of eucalyptus basal area and stand volume were highly correlated, with bootstrap based r 2 ranging from 0.61 to 0.89 and 0.67 to 0.88 respectively. Non-eucalyptus basal area r 2 ranged from 0.5 to 0.91.

Small mammals and retention islands: An experimental study of animal response to alternative logging practices

The integration of forest biodiversity conservation with wood production is a key part of ecologically sustainable forest management. This can be a particular challenge at the stand-level when high-intensity silvicultural systems like clearfelling are employed. Alternative logging practices to clearfelling that result in partial stand retention are being widely promoted in many parts of the world. We present new findings from a replicated block experiment designed to examine the responses of small terrestrial mammals to the retention of islands of forest within otherwise clearfelled harvest units. Our experiment was conducted in the Mountain Ash ( Eucalyptus regnans F. Muell) forests of the Central Highlands of Victoria, south-eastern Australia. We quantified the effects of four treatments on small terrestrial mammal abundance: (1) an uncut (‘control’) area of forest; (2) a 1.5 ha retained island within an otherwise clearfelled area; (3) three 0.5 ha retained ‘islands’ within an otherwise clearfelled area; and (4) a traditionally clearfelled area of forest, over the different stages of harvesting operations from pre-cut to post-cut to post-burn. We expected to find a gradient in animal abundance from controls to large islands to small islands to clearfelled areas. Our data revealed no difference in the small animal abundance in the controls and in the islands, but significantly lower numbers of animals in clearfelled areas, particularly after regeneration burning. We believe the reason for the strong negative effect of logging is associated with the near complete removal of vegetation cover immediately following traditional clearfelling operations. We expected that large islands (1.5 ha) would support more animals than small islands (0.5 ha), but we found no significant difference in animal abundance between large and small islands. Our results demonstrate that retained islands support populations of small mammals despite their abundance being very low in surrounding clearfelled areas. They also suggest that residual populations in islands may promote the process of post-disturbance ecological recovery in logged landscapes.

Comparing bird species richness and assemblage composition between montane ash eucalypt forest and cool temperate rainforests—an empirical study from Victoria, south-eastern Australia

Patterns of avian species richness and assemblage composition may change markedly between and within vegetation types. We compared bird species richness and assemblage composition in cool temperate rainforest and Mountain Ash (Eucalyptus regnans) forest in the Central Highlands of Victoria, south-eastern Australia. We quantified the effects of the age of stands of Mountain Ash on the extent of forest-type differences with cool temperate rainforest. We also explored the influence of the shape of stands of cool temperate rainforest on bird species richness and the composition of the bird assemblage. We found no significant differences in bird species richness between cool temperate rainforests and Mountain Ash forest. This result was consistent with subtle differences in the composition of the bird assemblage, with few bird taxa being totally excluded from either of the two forest types. Some species (e.g. Pink Robin (Petroica rodinogaster)) were significantly more likely to be recorded in cool temperate rainforest but were not uncommon in Mountain Ash forest. We found no evidence of significant effects of stand shape in cool temperate rainforest, which was consistent with analyses of bird assemblages given that most species occurred in both forest types. Hence, we uncovered no evidence of specialist taxa confined to cool temperate rainforest.

Long-term patterns in the decay, collapse, and abundance of trees with hollows in the mountain ash (Eucalyptus regnans) forests of Victoria, southeastern Australia

Large trees with hollows are an important component of stand structural complexity worldwide. Understanding their population dynamics is needed to manage cavity-dependent biota. We quantified long-term rates of collapse of 302 measured trees with hollows in 1939-aged regrowth mountain ash ( Eucalyptus regnans F. Muell.) forest in southeastern Australia. We identified time-dependent dynamics in which the collapse rates of trees slowed from ∼4% annually between 1983 and 1993 to ∼2.2% between 1993 and 2007. Transitions of trees between different decay states (forms) also slowed over time. Nevertheless, during the 24-year period of our study, over half of our marked and measured trees had fallen, but there was no recruitment of new trees with hollows. Under current projections, few trees with hollows will occur on our field sites by ∼2050, although more had been forecast in earlier investigations. Such a paucity of trees with hollows in extensive areas of regrowth mountain ash forests will lead to a shortage of nesting and sheltering sites for cavity-dependent biota. We suggest a short–medium (10- to 100-year) focus on the conservation of old growth and multi-aged stands will be needed to maintain populations of those species strongly associated with trees with hollows in mountain ash forests.