Fuel reduction is essential to mitigate the increasing risk of wildfire resulting from changes in land management and climate change. In Australia, planned burning is the predominant method employed to reduce surface fuels. Mechanical thinning offers an additional approach to reducing elevated fuels, albeit there has been little research into its efficacy in eucalypt forests. Here, we report the effects of commercial thinning on tree demography, aboveground fuel loads, microclimate, and modelled fire behaviour at three sites in Tasmanian tall eucalypt forest. Compared to unthinned forest, thinned coupes contained on average 75 % fewer live trees, 55 % less live stand basal area, 60 % less standing biomass and 14 % less above-ground biomass. Mechanical thinning redistributed biomass from standing biomass (average 206 Mg ha −1 more in unthinned) to surface fuels (152 Mg ha −1 more in thinned), with only 54 Mg ha −1 removed as harvested timber. Thinning increased daytime temperatures and lowered relative humidity, but effects on microclimate were small compared to the temporal fluctuations. Modelling under moderate fire weather suggests different fire behaviour between treatments, with thinned forests having more intense fires (fireline intensity 3.1 MW m −1 during moderate fire weather) and higher flames (4.3 m vs 3.4 m). In addition, large amounts of energy are embodied in localised debris piles with very high fuel loads. Application of the commercial thinning reported here does not reduce fire hazard. To do so demands drastically reducing debris through increased utilization of coarse woody debris and burning of fine residual fuels. • Thinning potentially reduces the fire hazard posed by dense forest regrowth. • We measured effect of thinning on biomass and surface fuels in eucalypt forest. • Thinning primarily redistributed biomass from standing biomass to surface fuels. • Utilising or burning debris following thinning is essential to reduce wildfire risk.

Elevated temperatures and extended drought periods are driving significant changes in the structure and function of forest ecosystems. High-elevation alpine ash forests (Eucalyptus delegatensis R.T. Baker) in Australia are an example of forests that are already impacted by climate change. These obligate seeder forests can shift to non-forest ecosystems following extreme drought and altered fire regimes, raising concern about their adaptation to a rapidly changing environment and long-term forest persistence. Plant functional traits play a major role in determining adaptive mechanisms to environmental conditions. While alpine ash forests are vulnerable to climate change, it is unclear if different provenances have adapted to the climatic conditions in which they grow. We therefore studied the variation in expression of functional traits related to drought tolerance in 21 provenances of alpine ash distributed across an environmental gradient. We investigated if functional traits varied between the provenances and were related to climate of origin in order to identify provenances that may be better adapted to drought. We measured the following traits in a common garden experiment under well-watered conditions: stomatal density, specific leaf area, minimum stomatal conductance and osmotic potential at full turgor. There was very little variation in trait expression between the 21 provenances for all functional traits related to drought tolerance. All provenances had medium-range stomatal density (170–300 stomata mm2) and specific leaf area (SLA, 50–70 cm2 g−1), a very low minimum stomatal conductance (2–4 mmol m2 s−1) and a high osmotic potential at full turgor (−0.6–0.7 MPa). There was no statistically significant correlation of trait expression with the climate of origin. Thus, there is very little evidence for genetically controlled differences in trait expression of drought tolerance traits in this species. It is likely that the high elevation and high rainfall environment of the species’ ecological niche has not been subjected to frequent and extensive drought periods that would elicit an evolutionary pressure selecting for drought-tolerant traits. We could not identify provenances that would have different drought-tolerant functional trait responses than others, potentially conferring an adaptive advantage under climate change. This has implications for using climate-adjusted provenancing to improve resilience in alpine ash forests predicted to experience more frequent and severe droughts in the future.

A significant increase in forest regeneration failure following logging is driven by climatic and management factors.

Increases in forest disturbances have altered global forest demography rates, with many regions now characterized by extensive areas of early-successional forest. Heterogeneity in the structure, diversity, and composition of early-successional forests influence their inherent ecological values from immediately following disturbance to later successional stages, including values for biodiversity and carbon storage. Here, using 14 years of longitudinal data, we describe patterns in the structure, richness, and composition of early-successional forests subject to one of three different disturbance types: (1) clearcut logging followed by slash burn, (2) severe wildfire followed by salvage logging, and (3) severe wildfire only, in the Mountain Ash (Eucalyptus regnans) and Alpine Ash (Eucalyptus delegatensis) forests of southeastern Australia. We also documented the influence of disturbance intervals (short, medium, and long) on early-successional forests. Our analyses revealed several key differences between forests that regenerated from wildfire versus two different anthropogenic perturbations. Most ash-type plant communities were resilient to wildfire within historical fire-regimes (75-150 years), exhibiting temporal trends of recovery in plant structure, richness, and composition within the first decade. In contrast, the richness, occurrence, and abundance of some plant lifeforms and life history traits were negatively associated with clearcut logging and salvage logging, relative to forests disturbed by wildfire alone. These included resprouting species, such as tree ferns and ground ferns. However, Acacia spp. and shrubs were more abundant after clearcut logging. Our findings also provide evidence of the pronounced negative impact of salvage logging on early-successional plant communities, relative to that of both clearcut logging and wildfire. Notably, plant richness declined for over a decade after salvage logging, rather than increased as occurred following other disturbance types. Early-successional forests provide the template for the stand structure and composition of mature forests. Therefore, altered patterns of recovery with different disturbance types will likely shape the structure and function of later-successional stages. Predicted increases in wildfire will increase the generation of early-successional forests and subsequent salvage logging. Therefore, it is pertinent that management consider how different disturbance types can produce alternate states of forest composition and structure early in succession, and the implications for mature stands.

This research presents a random forest classification approach to map the response of the obligate-seeder Eucalyptus species, Mountain Ash (Eucalyptus regnans) and Alpine Ash (E. delegatensis), to disturbance from timber harvesting in the Victorian Central Highlands in south-eastern Australia. A Sentinel-2 MultiSpectral Instrument (MSI) composite image was classified and analysed using a random forest algorithm trained using field data collected within fifty-three sites. Training and validation datasets were produced by randomly sub setting using a 70:30 split. Validation was performed by producing a confusion matrix using the points which were excluded from model training. The random forest model demonstrated strong performance at distinguishing Eucalyptus regrowth from the dominant understory species, Silver Wattle (Acacia dealbata), achieving an F1-score of 97.3% and true skill statistic of 96.4%.This study showcases the operational insights that satellite remote sensing data and machine learning can provide for regional-scale monitoring and management of E. regnans and E. delegatensis dominant ecosystems following disturbance. Due to the high conservation value of these communities, and their sensitivity to frequent high intensity disturbance and low precipitation during regeneration, this research seeks to provide a means to assess the condition of regenerating forest and in doing so enhance our understanding of these ecologically significant ecosystems in response to changing environmental conditions.

Abstract Plant growth is influenced by interactions with neighbouring plants. The strength and direction of the cumulative neighbourhood effect on growth can depend on neighbour properties, such as their abundance, size and proximity, as well as the degree of similarity between interacting plants and their traits, which can be captured by the species identity of neighbours. Such interactions are also influenced by the local environmental conditions that are largely determined by climate. Because neighbour and climatic effects are typically explored in isolation, particularly in long‐lived species such as trees, it is unclear how the impacts of neighbours on plant growth shift in response to temporal variation in climatic conditions. Here, we explored how neighbouring plants impact the annual growth of two eucalypts, Eucalyptus delegatensis and Eucalyptus regnans , over three growing seasons in an experimental forest in south‐east Tasmania, Australia. We assessed whether eucalypt growth rates could be described by the number, size, proximity, and species identity of neighbours, and how the strength of this effect was influenced by the growing season climatic conditions. We found that climate and neighbouring plants had an interactive impact on eucalypt growth. Neighbours had a consistent, competitive effect on the growth of both eucalypts in all three growing seasons which was strongly related to the cumulative neighbourhood biomass. The identity of neighbours was important in determining E. regnans growth only, whereby distinguishing neighbours according to functional group best described growth. Over all three growing seasons, we predicted that, on average, neighbours reduced E. delegatensis and E. regnans mean annual growth by 60.5% and 48.4%, respectively. However, the strength of the competitive effect of neighbours on eucalypt growth was related to growing season climate, being strongest when conditions were hot and dry and weakest in cool, wet conditions. Synthesis : Given the consistent results observed in two co‐occurring eucalypts, our findings suggest that drier and hotter climatic conditions increase the strength of competitive effects on tree growth. This has implications for future forest productivity given projected increased temperatures and variation in rainfall patterns globally.

ABSTRACT A population of Yellow-bellied Glider Petaurus australis on the Bago Plateau, on the NSW south-western slopes, was first surveyed across 126 sites in 1995 and this subsequently became the baseline for further population monitoring. A subset of 48 sites was resurveyed in 2010, and about one third of the sites (~40) were surveyed annually on a rotating panel between 2013–2019. Wildfire significantly impacted the Bago Plateau during 2020 and 51 sites were resurveyed post-fire in 2020/21. An occupancy modelling approach was used to estimate trends in occupancy between 1995 and 2020/21, including the influence of various covariates. Initial occupancy was positively associated with the extent of Montane Gums and mixed Wet Peppermint/Montane Gum forest types within a 450 m radius of the survey site. Supported models revealed that colonisation over time was positively associated with the density of hollow-bearing trees at a site, while extinction was positively associated with the extent of high severity wildfire at a site. Despite wide confidence intervals, the long-term occupancy trend showed a stable to slight increase between 1995 and 2019, but a ~26% reduction following wildfire. The increasing trend occurred despite a long-term rainfall deficit that was punctuated by occasional above average years during the survey period. There was no evidence that timber harvesting influenced occupancy by the gliders, although harvesting is predominantly focused within stands containing Alpine Ash Eucalyptus delegatensis, with monospecific stands generally avoided by the glider.

Quantifying the factors associated with the presence and abundance of species is critical for conservation. Here, we quantify the factors associated with the occurrence of the Southern Greater Glider in the forests of the Central Highlands of Victoria, south-eastern Australia. We gathered counts of animals along transects and constructed models of the probability of absence, and then the abundance if animals were present (conditional abundance), based on species' associations with forest type, forest age, the abundance of denning sites in large old hollow-bearing trees, climatic conditions, and vegetation density. We found evidence of forest type effects, with animals being extremely uncommon in Alpine Ash and Shining Gum forest. In Mountain Ash forest, we found a negative relationship between the abundance of hollow-bearing trees and the probability of Southern Greater Glider absence. We also found a forest age effect, with the Southern Greater Glider completely absent from the youngest sites that were subject to a high-severity, stand-replacing wildfire in 2009. The best fitting conditional abundance model for the Southern Greater Glider included a strong positive effect of elevation; the species was more abundant in Mountain Ash forests at higher elevations. Our study highlights the importance of sites with large old hollow-bearing trees for the Southern Greater Glider, although such trees are in rapid decline in Mountain Ash forests. The influence of elevation on conditional abundance suggests that areas at higher elevations will be increasingly important for the conservation of the species, except where Mountain Ash forest is replaced by different tree species that may be unsuitable for the Southern Greater Glider.

Vulnerability to xylem cavitation is a strong predictor of drought-induced damage in forest communities. However, biotic features of the community itself can influence water availability at the individual tree-level, thereby modifying patterns of drought damage. Using an experimental forest in Tasmania, Australia, we determined the vulnerability to cavitation (leaf P50 ) of four tree species and assessed the drought-induced canopy damage of 2944 6-yr-old trees after an extreme natural drought episode. We examined how individual damage was related to their size and the density and species identity of neighbouring trees. The two co-occurring dominant tree species, Eucalyptus delegatensis and Eucalyptus regnans, were the most vulnerable to drought-induced xylem cavitation and both species suffered significantly greater damage than neighbouring, subdominant species Pomaderris apetala and Acacia dealbata. While the two eucalypts had similar leaf P50 values, E. delegatensis suffered significantly greater damage, which was strongly related to the density of neighbouring P. apetala. Damage in E. regnans was less impacted by neighbouring plants and smaller trees of both eucalypts sustained significantly more damage than larger trees. Our findings demonstrate that natural drought damage is influenced by individual plant physiology as well as the composition, physiology and density of the surrounding stand.

Abstract AimMany species are adapted to a particular fire regime and major deviations from that regime may lead to localized extinction. Here, we quantify immaturity risks to an obligate‐seeder forest tree using an objectively designed climate model ensemble and a probabilistic fire regime simulator to predict future fire regimes.LocationAlpine ash (Eucalyptus delegatensis) distribution, Victoria, south‐eastern Australia.MethodsWe used a fire regime model (FROST) with six climate projections from a climate model ensemble across 3.7 million hectares of native forest and non‐native vegetation to examine immaturity risks to obligate‐seeder forests dominated by alpine ash (Eucalyptus delegatensis), which has a primary juvenile period of approximately 20 years. Our models incorporated current and future projected climate including fuel feedbacks to simulate fire regimes over 100 years. We then used Random Forest modelling to evaluate which spatial characteristics of the landscape were associated with high immaturity risks to alpine ash forest patches.ResultsSignificant shifts to the fire regime were predicted under all six future climate projections. Increases in both wildfire extent (total area burnt, area burnt at high intensity) and frequency were predicted with an average increase of up to 110 hectares burnt annually by short‐interval fires (i.e., within the expected minimum time to reproductive maturity). The immaturity risk posed by short‐interval fires to alpine ash forest patches was well explained by Random Forest models and varied with both location and environmental variables.Main conclusionsAlpine ash forests are predicted to be burned at greater intensities and shorter intervals under future fire regimes. About 67% of the current alpine ash distribution was predicted to be at some level of immaturity risk over the 100‐year modelling period, with the greatest risks to those patches located on the periphery of the current distribution, closer to roads or surrounded by a drier landscape at lower elevations.

Temporal patterns of vegetation recovery after wildfire in two obligate seeder ash forests

Abstract Large, high‐severity wildfires are an important component of disturbance regimes around the world and can influence the structure and function of forest ecosystems. Climatic changes and anthropogenic disturbances have altered global disturbance patterns and increased the frequency of high‐severity wildfires worldwide. While the recovery of plant communities at different successional stages after fire is well known, the influence of prior disturbances and stand age is poorly understood. Despite this, high‐intensity wildfires can produce long‐lasting legacy effects, which can influence the resistance and resilience of ecosystems. Here, we quantified the influence of prior stand age and disturbance history on the recovery of plant communities in the Mountain Ash and Alpine Ash forests of south‐eastern Australia after high‐severity wildfire. Specifically, controlling for stand age, we compared the abundance (percent cover) of different plant life forms and reproductive strategies in forests that were, at the time of high‐severity wildfire in 2009, “young” (28–35 yr old and previously logged), “mixed” age (26, 70–83, >150 yr old), “mature” (70–83 yr old), and “old‐growth” (>150 yr old). We uncovered evidence that the legacy of prior disturbance and stand age at the time of high‐severity wildfire can influence the recovery of plant communities in early successional forests. Specifically, we found that “young” forests burnt in 2009 had a higher abundance of ruderal and graminoid species, but had a lower abundance of persistent, onsite seeders, includingAcaciaand eucalypt species, relative to “old‐growth” forests burnt in 2009. “Mature” aged forests burnt in 2009 also had a lower abundance ofAcacia, eucalypt, and shrub species, relative to “old‐growth forests” burnt in 2009. Our findings provide evidence of advanced recovery in forests that were older when burnt by high‐severity wildfire, relative to younger forests burnt by the same wildfire. Further, we also demonstrate the influence of different environmental conditions on plant communities. In a period of rapid, global, environmental change, our study provides insights into the recovery of plant communities post‐wildfire with implications for forest management. Further, our findings suggest that predicted increases in the frequency of high‐severity wildfires may have consequences for forest regeneration.

Abstract Increased fire frequency can result in a decline of obligate seeding plants, which rely on re‐seeding for population persistence following canopy scorching fire. The resilience of obligate seeding plants to fire at any point in time depends on plant maturity and the size of plants in relation to potential fire scorch height. We investigated variation in the resilience of post‐fire regenerating Eucalyptus delegatensis subsp. delegatensis (alpine ash) to a short inter‐fire interval at its boundaries with E. fastigata (brown barrel) stands. The resilience of post‐fire E. delegatensis regeneration was modelled across these stand boundaries as a function of the height of the plants, their reproductive maturity and predicted fire behaviour derived from local fuel characteristics. We measured these attributes 14 years following the Canberra 2003 wildfires and stratified study sites by fire severity. The height and reproductive maturity of post‐fire E. delegatensis saplings decreased at stand boundaries with E. fastigata, while fuel was uniformly abundant and capable of supporting canopy scorching fire under mild fire weather conditions. This suggests that E. delegatensis is less resilient to frequent fire in the presence of interspecific competition and other environmental conditions that occur at stand boundaries, which represent the edge of the species’ realised niche. With forecasts for increased fire frequency in south eastern Australia, persistence of E. delegatensis may be greatest in pure stands corresponding to the core of the species’ realised niche, and in moist and sheltered topographic areas that are less prone to frequent canopy scorching fire. Our findings suggest the importance of considering fine‐scale spatial variation in important obligate seeding plant traits when predicting and managing the response of obligate seeding species to frequent fire.

Birds are high profile elements of the vertebrate biota in almost all terrestrial ecosystems worldwide. Many studies have uncovered evidence of a decline in bird biodiversity, but temporal patterns of change vary among ecosystems and among bird species with different life history traits. Ecosystem-specific, long-term studies are critical for identifying patterns of temporal change in bird biodiversity and the drivers of that change. Here we present a case study of drivers of temporal change in the bird fauna of the Mountain Ash and Alpine Ash eucalypt forests of south-eastern Australia. Using insights from observational studies and experiments conducted over the past 18 years, we discuss the direct and interactive effects of fire and logging on birds. The extent and severity of wildfires have major negative effects on almost all bird species, and have persisted for more than a decade after the last major conflagration (in 2009). Logging has markedly different effects on birds than those quantified for fire, and may have resulted in elevated levels of site occupancy in remaining uncut areas in the landscape. Both fire and logging have led to marked losses in the extent of old growth forest in Mountain Ash and Alpine Ash ecosystems. This is a concern given the strong association of most species of birds with old forest relative to younger age cohorts. Based on an understanding of the effects of fire and logging as drivers of change, we propose a series of inter-related management actions designed to enhance the conservation of avifauna in Mountain Ash and Alpine Ash ecosystems. A particular focus of management must be on increasing the interval between fires and limiting the spatial extent of wildfires and, in turn, significantly expanding the extent of old growth forest. This is because old growth forest is where most bird species are most likely to occur, and in the event of future wildfires, where fire severity will be lowest. Expansion of the old growth estate will require commercial logging operations to be excluded from large parts of Mountain Ash and Alpine Ash forests.

Understanding the factors controlling productivity is crucial for modelling current and predicting future forest growth and carbon sequestration potential. Although abiotic conditions exert a strong influence on productivity, it is becoming increasingly evident that plant community composition can dramatically influence ecosystem processes. However, much of our understanding of these processes in forests comes from correlative studies or field experiments in short-statured, short-lived vegetation. Here, we present the background, design and implementation success of the Australian Forest Evenness Experiment (AFEX), which was designed to investigate the influence of community composition on the processes that contribute to forest productivity. Eighty 25 × 25-m plots, covering 5 ha in a logged, burnt forest coupe in south-eastern Tasmania were sown with four tree species, namely Eucalyptus delegatensis R.T.Baker, E. regnans F.Muell., Acacia dealbata Link and Pomaderris apetala Labill., in varying combinations to provide a range of evenness levels with each of the four species as target dominant. Despite some differences between sown composition and realised composition 1 year after sowing, a substantial range of community evenness and local neighbourhood densities and compositions existed in the experiment. Thus, this site provides a unique opportunity to determine the influence of local neighbourhood composition on a range of ecological processes.

Occurrence points of Eucalyptus obliqua and Eucalyptus delegatensis in Tasmania from the Atlas of Living Australia (ALA) at March 2019, cleaned to remove suspected erroneous data and preserved specimens.

Variation in Eucalyptus delegatensis post-fire recovery strategies: The Tasmanian subspecies is a resprouter whereas the mainland Australian subspecies is an obligate seeder

Abstract Landscape change and habitat fragmentation is increasingly affecting forests worldwide. Assessments of patterns of spatial cover in forests over time can be critical as they reveal important information about landscape condition. In this study, we assessed landscape patterns across the Mountain Ash (Eucalyptus regnans) and Alpine Ash (Eucalyptus delegatensis) forests in the Central Highlands of Victoria between 1999 and 2019. These forests have experienced major disturbance over the past 20 years through a major fire (in 2009) and extensive industrial logging. We found that around 70% and 65% of the Mountain Ash and Alpine Ash forest areas, respectively, were either disturbed or within 200 m of a disturbed area. Inclusion of planned logging increased these disturbance categories to 72% and 70%, respectively. We also found that the isolation of Mountain Ash core areas (patches of undisturbed forest >1000 ha) increased significantly (P < 0.05) over our study period, with the proximity between disturbed areas conversely increasing significantly (P < 0.05). This means that continued and planned disturbance through industrial logging will have an amplified adverse effect on remaining undisturbed ash forest patches, which will become smaller and more dispersed across the landscape.

Key perspectives on early successional forests subject to stand-replacing disturbances

The aim of this study was to investigate the process of drying Eucalyptus delegatensis in a greenhouse solar kiln. Specific objectives were to assess stress formation, moisture gradients and timber distortion, the moisture content distribution within various sections of the timber stack, and internal checking and collapse development within the boards. The maximal temperature and relative humidity (RH) in the daytime were set at 43 °C/72% RH. At night time, the temperature was at ambient condition with 90% RH. The strain measurements were undertaken before and after the samples were sliced. The timber quality at the end of drying was assessed based on Australian and New Zealand standard (AS/NZS 4787:2001). The moisture content values in the three different sections (front, middle and end) of 2400 mm long boards were compared by Analysis of Variance. The results showed that the mean compressive strain was − 2 × 10− 4 mm/mm in the core layers and the tensile strain was 14 × 10− 4 mm/mm in the outer layers. All sample boards were within the acceptable limits for cupping, spring and bow, even though the relative humidity level did not reach the set value. However, the amount of twist in three out of twelve sample boards was above the acceptable limit. Mean moisture gradient was 0.6%. There was a significant difference in moisture content at the end section compared to the front and middle sections. Internal checking, collapse and residual stress were graded as Class “C” (class A is the highest grade and D is the lowest).