Forests Of South-eastern Australia Research Articles

Wombat burrows are hotspots for small vertebrates in a landscape subject to gigafire

Abstract Ecosystem engineers modify their environment and influence the availability of resources for other organisms. Burrowing species, a subset of allogenic engineers, are gaining recognition as ecological facilitators. Burrows created by these species provide habitat for a diverse array of other organisms. Following disturbances, burrows could also serve as ecological refuges, thereby enhancing ecological resistance to disturbance events. We explored the ecological role of Common Wombat (Vombatus ursinus) burrows using camera traps in forests of southeastern Australia. We compared animal activity at paired sites with and without burrows, from the same fire severity class and habitat. We examined how animal activity at Common Wombat burrows was affected by the 2019–20 Black Summer bushfires in Australia. We predicted that burrows would serve as hotspots for animal activity and as refuges in burned areas. The activity of several species including Bush Rat (Rattus fuscipes), Agile Antechinus (Antechinus agilis), Lace Monitor (Varanus varius), Painted Button-quail (Turnix varius), and Grey Shrike-thrush (Colluricincla harmonica) increased at sites where Common Wombat burrows were present, while other species avoided burrows. Species that were more active at burrows tended to be smaller mammal and bird species that are vulnerable to predation, whereas species that avoided burrows tended to be larger mammals that might compete with Common Wombat for resources. Species composition differed between sites with and without burrows, and burrow sites had higher native mammal species richness. The association of several species with burrows persisted or strengthened in areas that burned during the 2019–20 Black Summer bushfires, suggesting that Common Wombat burrows may act as ecological refuges for animals following severe wildfire. Our findings have relevance for understanding how animals survive, persist, and recover following extreme wildfire events.

Incorporating burn heterogeneity with fuel load estimates may improve fire behaviour predictions in south-east Australian eucalypt forest

Background Simulations of fire spread are vital for operational fire management and strategic risk planning. Aims To quantify burn heterogeneity effects on post-fire fuel loads, and test whether modifying fuel load estimates based on the fire severity and patchiness of the last fire improves the accuracy of simulations of subsequent fires. Methods We (1) measured fine fuels in eucalypt forests in south-eastern Australia following fires of differing severity; (2) modified post-fire fuel accumulation estimates based on our results; and (3) ran different fire simulations for a case-study area which was subject to a planned hazard reduction burn followed by a wildfire shortly thereafter. Key results Increasing fire severity resulted in increased reduction in bark fuels. In contrast, surface and elevated fuels were reduced by similar amounts following both low-moderate and high-extreme fire severity. Accounting for burn heterogeneity, and fire severity effects on bark, improved the accuracy of fire spread for a case study fire. Conclusions Integration of burn heterogeneity into post-burn fuel load estimates may substantially improve fire behaviour predictions. Implications Without accounting for burn heterogeneity, patchy burns of low severity may mean that risk estimations are incorrect. This has implications for evaluating the cost-effectiveness of planned burn programmes.

Moisture thresholds for ignition vary between types of eucalypt forests across an aridity gradient

ContextQuantifying spatial and temporal variations in landscape flammability is important for implementing ecologically desirable prescribed burns and gauging the level of fire risk across a landscape. Yet there is a paucity of models that provide adequate spatial detail about landscape flammability for these purposes.ObjectivesOur aim was to quantify spatial and temporal variations in ignitability across a forested landscape. We asked: (1) How do fuel moisture and meteorological variables interact to affect ignitability? (2) Do fuel moisture thresholds for ignition vary across a gradient of forest types? (3) How does the spatial connectivity of ignitable fuel vary over time? (4) How could an ignitability model be used to inform fire management decision-making?MethodsWe conducted field-based ignition tests with flaming firebrands over three fire seasons. Ignitions were attempted across a range of moisture and meteorological conditions at 15 sites in eucalypt forest in south-eastern Australia. Structural equation modelling and generalized linear models were used to quantify relationships between ignitability, aridity, fuel moisture and weather.ResultsThe strongest predictors of ignitability were the moisture content of dead near surface fine fuel and in-forest vapour pressure deficit. Ignition thresholds for both varied across an aridity gradient. Dense forests (i.e., wet and damp eucalypt forests) needed drier fuel and drier in-forest atmospheric conditions to ignite than sparser forests (i.e., shrubby foothill forest).ConclusionOur modelling of ignitability could inform fire planning in south-eastern Australia and the methodology could be applied elsewhere to develop similar models for other regions. Days with consistently high ignitability across the landscape are more conducive to the development of large wildfires whereas days when ignitability is spatially variable are more suitable for prescribed burning.

An instructional workflow for using terrestrial laser scanning (TLS) to quantify vegetation structure for wildlife studies

Vegetation structure is a crucial component of habitat suitability for wildlife, but methods traditionally used to quantify it can be costly, subjective, or difficult to replicate. There have been substantial advancements, and growing interest, in the use of terrestrial laser scanning (TLS) methods to measure fine-scale vegetation attributes in ecological research, but limited opportunities for ecologists and practitioners to learn how to incorporate these into applied research. Here, we provide a starting point for those who want to incorporate TLS methods into ecological research and monitoring, using a case study from a temperate forest in South-Eastern Australia. We scanned 24 sites at different stages of post-fire recovery as part of a larger project measuring the impact of fire on forest dwelling bats, using a FARO Focus 3DS. Using the data from these scans, we present an example workflow with accompanying R code to demonstrate how to process the point clouds and extract a range of vegetation structure metrics relevant to habitat structure for wildlife, including vegetation height, cover, density, and heterogeneity. We discuss how three-dimensional data obtained through TLS can be valuable to wildlife studies and opens up the potential to explore advanced ecological and conservation questions around how vegetation structure influences wildlife behaviours, distribution patterns, and responses to disturbance.

Acacia Density, Edaphic, and Climatic Factors Shape Plant Assemblages in Regrowth Montane Forests in Southeastern Australia

A fundamental requirement of sustainable forest management is that stands are adequately regenerated after harvesting. To date, most research has focused on the regeneration of the dominant timber species and to a lesser degree on plant communities. Few studies have explored the impact of the regeneration success of dominant tree species on plant community composition and diversity. In this study, we quantified the influence of variability in tree density and climatic and edaphic factors on plant species diversity in montane regrowth forests dominated by Eucalyptus regnans in the Central Highlands of Victoria in southeastern Australia. We found that Acacia density shaped plant biodiversity more than Eucalyptus density. Edaphic factors, particularly soil nutrition and moisture availability, played a significant role in shaping species turnover and occurrence. Our findings suggest that the density of Acacia is a key biotic filter that influences the occurrence of many understorey plant species and shapes plant community turnover. This should be considered when assessing the impacts of both natural and anthropogenic disturbances on plant biodiversity in the montane forests of southeastern Australia.

Interpreting water demands of forests and grasslands within a new Budyko formulation of evapotranspiration using percolation theory

The relationship between carbon cycle and water demand is key to understanding global climate change, vegetation productivity, and predicting the future of water resources. The water balance, which enumerates the relative fractions of precipitation P that run off, Q, or are returned to the atmosphere through evapotranspiration, ET, links drawdown of atmospheric carbon with the water cycle through plant transpiration. Our theoretical description based on percolation theory proposes that dominant ecosystems tend to maximize drawdown of atmospheric carbon in the process of growth and reproduction, thus providing a link between carbon and water cycles. In this framework, the only parameter is the fractal dimensionality df of the root system. Values of df appear to relate to the relative roles of nutrient and water accessibility. Larger values of df lead to higher ET values. Known ranges of grassland root fractal dimensions predict reasonably the range of ET(P) in such ecosystems as a function of aridity index. Forests with shallower root systems, should be characterized by a smaller df and, therefore, ET that is a smaller fraction of P. The prediction of ET/P using the 3D percolation value of df matches rather closely results deemed typical for forests based on a phenomenology already in common use. We test predictions of Q with P against data and data summaries for sclerophyll forests in southeastern Australia and the southeastern USA. Applying PET data from a nearby site constrains the data from the USA to lie between our ET predictions for 2D and 3D root systems. For the Australian site, equating cited “losses” with PET underpredicts ET. This discrepancy is mostly removed by referring to mapped values of PET in that region. Missing in both cases is local PET variability, more important for reducing data scatter in southeastern Australia, due to the greater relief.

Canopy Composition and Spatial Configuration Influences Beta Diversity in Temperate Regrowth Forests of Southeastern Australia

Structural features of the overstorey in managed and unmanaged forests can significantly influence plant community composition. Native Acacia species are common in temperate eucalypt forests in southeastern Australia. In these forests, intense disturbances, such as logging and wildfire, lead to high densities of regenerating trees, shrubs, and herbs. The tree layer is dominated by Acacia and Eucalyptus, that compete intensely for resources in the first decades after stand establishment. The relative abundance and size of Acacia and Eucalyptus varies widely due to stochastic factors such as dispersal, microsite variability, and weather and climatic conditions. This variability may influence the structure and composition of the herbaceous and shrub species. In the temperate forests of southeastern Australia, understorey plant diversity is assumed to be influenced by Acacia species density, rather than Eucalyptus density. To quantify the influence of Acacia and Eucalyptus density on plant community composition, we used remote sensing and machine learning methods to map canopy composition and then compare it to understorey composition. We combined unoccupied aerial vehicle (UAV or drone) imagery, supervised image classifications, and ground survey data of plant composition from post-logging regrowth forests in the Central Highlands of southeastern Australia. We found that aggregation and patch metrics of Eucalyptus and Acacia were strongly associated with understorey plant beta diversity. Increasing aggregation of Acacia and the number of Acacia patches had a significant negative effect on plant beta diversity, while the number of Eucalyptus patches had a positive influence. Our research demonstrates how accessible UAV remote sensing can be used to quantify variability in plant biodiversity in regrowth forests. This can help forest managers map patterns of plant diversity at the stand-scale and beyond to guide management activities across forested landscapes.

The characteristics of regeneration failure and their potential to shift wet temperate forests into alternate stable states

Under the current trajectory of accelerated climatic and environmental change, many forests are at risk of regeneration failure and subsequent transition to alternate stable states including non-forests or grassland. These regimes shifts can have severe ecological impacts and compromise carbon stores, undermine climate change mitigation, and create conditions incompatible with the survival of biodiversity. However, detailed empirical-based understanding of the alternative states associated with disturbance regime shifts is limited. Here, using a manipulative experiment, and controlling for seed application, we document temporal patterns of vegetation structure and composition associated with regeneration failure after clearcut logging in the ash-type eucalypt forests in south-eastern Australia. Our findings clearly demonstrate that in the absence of direct seed input, frequent stand-replacing disturbance can result in regeneration failure in these forests leading to them being replaced by low species diversity Acacia woodland. These insights can be extrapolated to scenarios of post-fire regeneration failure, where frequent fire precludes the development of adequate seed-stores (<21 years). Such shifts to alternative stable states can have severe ecological implications which require management intervention to circumvent and conserve the functional integrity of these forests. Our case study demonstrates the value of manipulative empirical experiments in quantifying the potential aftermath of forest regeneration failure. Such experiments may be useful to support theories and models in quantifying the ecological implications of regeneration failure, and to guide the application of management interventions for restoration where empirical-based knowledge of these states is limited.

First records of Tumerozetidae and Nodocepheidae from Australia, with descriptions of new taxa and a re-assessment of the Polypterozetoidea (Oribatida, Brachypylina)

New species and a new genus of polypterozetoid oribatid mite are described from wet habitats in forests in south-eastern Australia: Tumerozetes roughleyi sp. nov. (Tumerozetidae), Nodocepheus luxtoni sp. nov. and Sacculella yarra gen. et sp. nov. (Nodocepheidae). The superfamily Polypterozetoidea has not been recorded previously from Australia. Tumerozetes roughleyi sp. nov. and Sacculella yarra gen. et sp. nov. were recorded from temperate Nothofagus cunninghami rainforest in central Victoria. Nodocepheus luxtoni sp. nov. was recorded from temperate rainforest in Tasmania and eastern Victoria. Tumerozetes was known previously only from New Zealand, and Nodocepheus from New Zealand, southern Africa and south-central America. The definitions of Tumerozetidae and Nodocepheidae are revised in the light of observations on the morphology of these new species, and their phylogenetic and biogeographical affinities with other members of the Polypterozetoidea are considered.

Disturbance causes variation in sub-canopy fire weather conditions

Disturbance history is known to affect fire risk by altering fuel dynamics, but the effects of disturbance on micro-meteorological conditions that influence fire are poorly understood. Logging and wildfire can significantly alter the height and density of vegetation in forests. These structural attributes can influence aspects of the sub-canopy microclimate that may influence forest flammability. We used portable weather stations to measure the effects of time since logging and time since wildfire on air temperature, relative humidity, vapour pressure deficit and windspeed at 119 sites in coastal forest in south-eastern Australia. These data were used to calculate fuel moisture and within forest Forest Fire Danger Index (FFDI). Data were collected on 345 days (12 days per site on average), over three consecutive fire seasons. Temperature, vapour pressure deficit, windspeed and forest FFDI all decreased with time since logging, while relative humidity and fuel moisture content increased. Windspeeds also decreased with time since wildfire. These effects continued for at least 60 years after disturbance. Over the duration of our study, fuel was available to burn (below 16% fuel moisture content) 1.4 times more often in recently logged sites (zero years since logging) compared to sites that had not been logged for 71 years. Recently logged sites were also predicted to have a high Fire Danger Rating (FFDI = 12–24) on 24 days, compared to just two days at sites last logged 71 years ago. Our findings indicate that the changes in vegetation associated with logging and to a lesser extent wildfire, increase the risk of fire. This research provides new insights into the effects of antecedent logging and wildfire on forest flammability that can be used to inform the management of fire prone forests.

Predicting ignitability from firebrands in mature wet eucalypt forests

Forest ignitability varies spatially and temporally across landscapes as a function of fuel moisture. Wetter forests are often more difficult to ignite and therefore act as a barrier to the spread of wildfire. However, when these forests dry out and transition to an ignitable-state, the landscape is primed for large wildfires. Fire managers require information about forest ignitability to predict the timing of this switch. Yet, an understanding of the drivers and thresholds for ignitability in wetter forests remains incomplete. Our study sought to address this knowledge gap by evaluating a range of in-forest and landscape variables as predictors of ignitability in wet eucalypt forests. We conducted ignition experiments over two fire seasons at six sites in mature wet and damp eucalypt forest in south-eastern Australia. Each experiment involved 30 ignition attempts within each site on a single day using two types of flaming firebrands with different heats of combustion. The success and sustainability of each ignition attempt was recorded and this process repeated 8–9 times per site culminating in 1590 ignition attempts across a range of fuel moisture conditions. Ignition results were evaluated against 21 different in-forest and landscape variables. In-forest variables were generally stronger predictors of ignition and sustained ignition than landscape variables. The more energetic firebrand yielded more successful ignitions and sustained ignitions, but rankings for the predictor variables were similar for both types of firebrand. The strongest predictor of ignition and sustained ignition was in-forest vapour pressure deficit (VPD) (R2 = 0.65 for ignition and R2 = 0.55 sustained ignition), which is a measure of atmospheric dryness that is strongly associated with dead fuel moisture content. Past studies have identified strong links between VPD, burned area and fire severity at broader spatial and temporal scales. Our results show that VPD is also important at the time of ignition and could be used to predict wildfire risk in wet eucalypt forests.

Post-fire pickings: Large herbivores alter understory vegetation communities in a coastal eucalypt forest.

Fire and herbivores alter vegetation structure and function. Future fire activity is predicted to increase, and quantifying changes in vegetation communities arising from post‐fire herbivory is needed to better manage natural environments. We investigated the effects of post‐fire herbivory on understory plant communities in a coastal eucalypt forest in southeastern Australia. We quantified herbivore activity, understory plant diversity, and dominant plant morphology following a wildfire in 2017 using two sizes of exclosures. Statistical analysis incorporated the effect of exclusion treatments, time since fire, and the effect of a previous prescribed burn. Exclusion treatments altered herbivore activity, but time since fire did not. Herbivory reduced plant species richness, diversity, and evenness and promoted the dominance of the most abundant plants within the understory. Increasing time since fire reduced community diversity and evenness and influenced morphological changes to the dominant understory plant species, increasing size and dead material while decreasing abundance. We found the legacy effects of a previous prescribed burn had no effect on herbivores or vegetation within our study. Foraging by large herbivores resulted in a depauperate vegetation community. As post‐fire herbivory can alter vegetation communities, we postulate that management burning practices may exacerbate herbivore impacts. Future fire management strategies to minimize herbivore‐mediated alterations to understory vegetation could include aggregating management burns into larger fire sizes or linking fire management with herbivore management. Restricting herbivore access following fire (planned or otherwise) can encourage a more diverse and species‐rich understory plant community. Future research should aim to determine how vegetation change from post‐fire herbivory contributes to future fire risk.

Stand age related differences in forest microclimate

Quantifying spatio-temporal variation in forest microclimate is important to understand the habitat associations of some species, identify potential refugia, and manage forests in a changing climate. We quantified relationships between microclimatic conditions and stand age using a detailed case study of the Mountain Ash (Eucalyptus regnans) forests in south-eastern Australia. We deployed sensor buttons to capture data on day-time and night-time seasonal (Julian Day) temperature profiles in even-aged stands that were 12-years-old, 30–40-years-old, ∼82–95-years-old, and 200+ -years-old. We constructed Bayesian generalised linear models (GLMs) to quantify the main and interacting effects of stand age and topographic factors and foliage cover on seasonal profiles for: median, maximum and variability in day-time and night-time temperature.The most parsimonious model for median day-time temperature included a main effect of midstory and overstory cover, both of which were inversely related to median day-time temperature. The most parsimonious model for median night-time temperature measures included an additive effect of forest age and seasonality. Temperatures for the youngest forests (that were 12-years-old) were different from other age classes and were characterised by the lowest median and minimum night-time temperatures.The most parsimonious model for day-time maximum temperature and day-time interquartile range included an interaction between forest age and Julian day. Day-time maximum temperatures were warmest in 12-year-old forest. The coolest maximum day-time temperatures in summer were generally in old growth stands (200+ -year-old). The greatest variability in maximum day-time temperatures was in 12-year-old forest whereas, in general, old growth stands experienced the least variable day-time temperatures. Our sensor data also showed that old growth forests were characterised by fewer days above 30, 35 and 40 degrees than 12-year old forest. Our empirical data contain compelling evidence that the youngest forests were characterised by the hottest day-time temperatures, the coldest night-time temperatures, and the most variable day-time and night-time temperature regimes. Age class differences in stand structure (e.g. canopy height, prevalence of large old trees and dense wet understorey) may explain stand age related seasonal differences in local microclimatic conditions.

Species and Competition Interact to Influence Seasonal Stem Growth in Temperate Eucalypts

Insights on tree species and competition effects on seasonal stem growth are critical to understanding the impacts of changing climates on tree productivity, particularly for eucalypts species that occur in narrow climatic niches and have unreliable tree rings. To improve our understanding of climate effects on forest productivity, we examined the relative importance of species, competition and climate to the seasonal stem growth of co-occurring temperate eucalypts. We measured monthly stem growth of three eucalypts (Eucalyptus obliqua, E. radiata, and E. rubida) over four years in a natural mixed-species forest in south-eastern Australia, examining the relative influences of species, competition index (CI) and climate variables on the seasonal basal area increment (BAI). Seasonal BAI varied with species and CI, and was greatest in spring and/or autumn, and lowest in summer. Our study highlights the interactive effects of species and competition on the seasonal stem growth of temperate eucalypts, clearly indicating that competitive effects are strongest when conditions are favourable to growth (spring and autumn), and least pronounced in summer, when reduced BAI was associated with less rainfall. Thus, our study indicates that management to reduce inter-tree competition would have minimal influence on stem growth during less favourable (i.e., drier) periods.

A Predictive Model of Leaf Flammability Using Leaf Traits and Radiant Heat Flux for Plants of Fire-Prone Dry Sclerophyll Forest

The differential flammability of individual plant species in landscape-scale fire behaviour is an important consideration, but one that is often overlooked. This is in part due to a relative dearth in the availability of plant flammability data. Here, we present a highly accurate predictive model of the likelihood of plant leaves entering flaming combustion as a function of leaf mass per area (LMA), leaf area (LA) and radiant heat flux using species of fire-prone dry sclerophyll forests of south-eastern Australia. We validated the performance of the model on two separate datasets, and on plant species not included in the model building process. Our model gives accurate predictions (75–84%) of leaf flaming with potential application in the next generation of fire behaviour models. Given the global wealth of species’ data for LMA and LA, in stark contrast to leaf flammability data, our model has the potential to improve understanding of forest flammability in the absence of leaf flammability information.

Dingoes have greater suppressive effect on fox populations than poisoning campaigns

The mesopredator release hypothesis predicts that abundance of smaller predators should increase in the absence of larger predators due to release from direct killing and competition. However, the effects of top predators on mesopredators are unlikely to operate in isolation but interact with other factors such as primary productivity of the landscape and human activities. We investigate factors influencing activity indices of a top predator (dingo) and an introduced mesopredator (red fox) in forests of south-eastern Australia. We used generalised linear models to investigate the effects that net primary productivity, proximity to freehold land and poison baiting campaigns directed at dingoes had on fox and dingo activity. Baiting was the best predictor of activity for both dingoes and foxes. Dingo activity was variable but typically lower at baited sites. Fox activity varied within a lower range at a majority of sites compared to the dingo but was typically higher at the baited sites. Positive responses of foxes to dingo control are consistent with the mesopredator release hypothesis and suggest in this region dingoes may have greater suppressive effect on fox populations than poisoning campaigns directed towards dingoes. Our results suggest that removal of dingoes may be counter-productive for biodiversity conservation because it may lead to higher activity of foxes.

Mapping canopy nitrogen-scapes to assess foraging habitat for a vulnerable arboreal folivore in mixed-species Eucalyptus forests.

Herbivore foraging decisions are closely related to plant nutritional quality. For arboreal folivores with specialized diets, such as the vulnerable greater glider (Petauroides volans), the abundance of suitable forage trees can influence habitat suitability and species occurrence. The ability to model and map foliar nitrogen would therefore enhance our understanding of folivore habitat use at finer scales. We tested whether high‐resolution multispectral imagery, collected by a lightweight and low‐cost commercial unoccupied aerial vehicle (UAV), could be used to predict total and digestible foliar nitrogen (N and digN) at the tree canopy level and forest stand‐scale from leaf‐scale chemistry measurements across a gradient of mixed‐species Eucalyptus forests in southeastern Australia. We surveyed temperate Eucalyptus forests across an elevational and topographic gradient from sea level to high elevation (50–1200 m a.s.l.) for forest structure, leaf chemistry, and greater glider occurrence. Using measures of multispectral leaf reflectance and spectral indices, we estimated N and digN and mapped N and favorable feeding habitat using machine learning algorithms. Our surveys covered 17 Eucalyptus species ranging in foliar N from 0.63% to 1.92% dry matter (DM) and digN from 0.45% to 1.73% DM. Both multispectral leaf reflectance and spectral indices were strong predictors for N and digN in model cross‐validation. At the tree level, 79% of variability between observed and predicted measures of nitrogen was explained. A spatial supervised classification model correctly identified 80% of canopy pixels associated with high N concentrations (≥1% DM). We developed a successful method for estimating foliar nitrogen of a range of temperate Eucalyptus species using UAV multispectral imagery at the tree canopy level and stand scale. The ability to spatially quantify feeding habitat using UAV imagery allows remote assessments of greater glider habitat at a scale relevant to support ground surveys, management, and conservation for the vulnerable greater glider across southeastern Australia.

Differing regeneration patterns after catastrophic fire and clearfelling: Implications for future stand dynamics and forest management

Silvicultural systems in native forests typically attempt to mimic natural disturbance regimes to ensure that the dominant tree species and associated biodiversity persist. Where the disturbance regime is driven by catastrophic, stand-replacing disturbances, such as fire and windstorms, even-aged (or single-cohort) silvicultural systems such as clearfelling (clearcutting) are commonly applied. However, there are important differences between stand-replacing natural disturbances and clearfelling. Considerable attention has focused on the biological legacies that persist after these disturbances (e standing dead trees, coarse woody debris). However, the inherent variability in regeneration patterns, which will drive long-term stand development patterns over the coming decades and centuries, has been largely overlooked. In this study we take advantage of a catastrophic fire event to compare patterns of regeneration for a dominant tree species after a high-intensity natural disturbance and after clearfelling. We focused on the mountain ash (Eucalyptus regnans F. Muell.) forests of southeastern Australia that were burned in the 2009 Black Saturday fire complex and are typically managed through clearfelling. We surveyed mountain ash seedling density in 24,200 quadrats across 121 plots (35 clearfelled, 86 burnt). We developed a statistical model to characterise the abundance and variability of seedling density. Our results demonstrated that natural regeneration density after the 2009 fires was nearly two times greater than regeneration at clearfelled sites that was aerially sown by helicopter. More importantly, however, the over-dispersion parameter in our model was nearly four times greater in the clearfelled sites than in the fire sites, meaning that regeneration in the clearfelled sites was much more spatially uniform than in the fire-affected sites. More than 50% of the surveyed quadrats in the fires sites had no mountain ash seedlings. The highly patchy distribution of natural regeneration has important implications for future stand development. Over time, patchy regeneration leads to structural variability that can benefit wildlife habitat and forest resilience to disturbances. A comparison of diameter distributions of stands that established at very different initial densities after the catastrophic 1939 fires shows the importance of early density on future stand structure. Our results provide an ecological basis for modifying current regeneration practices to better align contemporary forest management with natural disturbance regimes.

Temporal patterns of forest seedling emergence across different disturbance histories.

Forest ecosystems experience a myriad of natural and anthropogenic disturbances that shape ecological communities. Seedling emergence is a critical, preliminary stage in the recovery of forests post​ disturbance and is triggered by a series of abiotic and biotic changes. However, the long‐term influence of different disturbance histories on patterns of seedling emergence is poorly understood.Here, we address this research gap by using an 11‐year dataset gathered between 2009 and 2020 to quantify the influence of different histories of natural (wildfire) and anthropogenic (clearcut and postfire salvage logging) disturbances on emerging seedlings in early‐successional Mountain Ash forests in southeastern Australia. We also describe patterns of seedling emergence across older successional forests varying in stand age (stands that regenerated in <1900s, 1939, 1970–90, and 2007–11).Seedling emergence was highest in the first three years post disturbance. Stand age and disturbance history significantly influenced the composition and abundance of plant seedlings. Specifically, in salvage‐logged forests, plant seedlings were the most different from similarly aged forests with other disturbance histories. For instance, relative to clearcut and unlogged, burnt forests of the same age, salvage logging had the lowest overall richness, the lowest counts of Acacia seedlings, and an absence of common species including Acacia obliquinervia, Acacia frigescens, Cassinia arcuealta, Olearia argophylla, Pimelea axiflora, Polyscias sambucifolia, and Prosanthera melissifolia over the survey period. Synthesis: Our findings provide important new insights into the influence of different disturbance histories on regenerating forests and can help predict plant community responses to future disturbances, which may influence forest recovery under altered disturbance regimes.

Quantitative Analysis of Forest Fires in Southeastern Australia Using SAR Data

Prescribed burning is a common strategy for minimizing forest fire risk. Fire is introduced under specific environmental conditions, with explicit duration, intensity, and rate of spread. Such conditions deviate from those encountered during the fire season. Prescribed burns mostly affect surface fuels and understory vegetation, an outcome markedly different when compared to wildfires. Data on prescribed burning are crucial for evaluating whether land management targets have been reached. This research developed a methodology to quantify the effects of prescribed burns using multi-temporal Sentinel-1 Synthetic Aperture Radar (SAR) imagery in the forests of southeastern Australia. C-band SAR datasets were specifically used to statistically explore changes in radar backscatter coefficients with the intensity of prescribed burns. Two modeling approaches based on pre- and post-fire ratios were applied for evaluating prescribed burn impacts. The effects of prescribed burns were documented with an overall accuracy of 82.3% using cross-polarized backscatter (VH) SAR data under dry conditions. The VV polarization indicated some potential to detect burned areas under wet conditions. The findings in this study indicate that the C-band SAR backscatter coefficient has the potential to evaluate the effectiveness of prescribed burns due to its sensitivity to changes in vegetation structure.