School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemThe influence of spatial patterns in foraging habitat on the abundance and home range size of a vulnerable arboreal marsupial in southeast Australia(WILEY, 2021-12)Abstract Wildlife can persist in a range of landscape configurations, but population densities can vary due to resource availability. Resources and environmental conditions shaping habitat suitability may be spatially dispersed or clumped, which can drive habitat availability. We explored how spatial configuration and aggregation of favorable feeding resources and climatic conditions affect populations of the greater glider (Petauroides volans), an arboreal marsupial in southeast Australia, vulnerable to climate change and disturbances. We hypothesized home‐range functionality from literature and field observations and used a generalized spatial framework based on neutral landscape models to test how spatial aggregation influences home‐range sizes and population structure. At the landscape scale, any decrease in climatic suitability also decreased potential population density, independent of the initial spatial configuration of the feeding landscape. At the stand scale however, the spatial configuration of feeding habitat drove population density. Dispersed resources required increased home‐range sizes for individual greater gliders to obtain feeding resources and resulted in smaller populations. Clumped resources supported larger populations, even when only small fractions of the stand contained feeding habitat. Disturbances to these resources could either retain populations or lead to extinction, depending on spatial aggregation and disturbance intensity. Increasingly severe dispersed disturbances caused potential home ranges to disappear more rapidly and remaining home ranges to become larger and contain less feeding habitat. The ability of greater gliders to establish populations and persist under disturbance was therefore highly dependent on the spatial aggregation of habitat resources and the type and severity of disturbance. Changes in climate act at a different scale and may override favorable habitat conditions at the stand level. Our results have implications for the conservation and retention of critical feeding habitat for greater gliders and provide insights into important factors to ensure population persistence under climate change and forest management.
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ItemEvaluating the dendroclimatological potential of blue intensity on multiple conifer species from Tasmania and New Zealand(COPERNICUS GESELLSCHAFT MBH, 2021-12-14)Abstract. We evaluate a range of blue intensity (BI) tree-ring parameters in eight conifer species (12 sites) from Tasmania and New Zealand for their dendroclimatic potential, and as surrogate wood anatomical proxies. Using a dataset of ca. 10–15 trees per site, we measured earlywood maximum blue intensity (EWB), latewood minimum blue intensity (LWB), and the associated delta blue intensity (DB) parameter for dendrochronological analysis. No resin extraction was performed, impacting low-frequency trends. Therefore, we focused only on the high-frequency signal by detrending all tree-ring and climate data using a 20-year cubic smoothing spline. All BI parameters express low relative variance and weak signal strength compared to ring width. Correlation analysis and principal component regression experiments identified a weak and variable climate response for most ring-width chronologies. However, for most sites, the EWB data, despite weak signal strength, expressed strong coherence with summer temperatures. Significant correlations for LWB were also noted, but the sign of the relationship for most species is opposite to that reported for all conifer species in the Northern Hemisphere. DB results were mixed but performed better for the Tasmanian sites when combined through principal component regression methods than for New Zealand. Using the full multi-species/parameter network, excellent summer temperature calibration was identified for both Tasmania and New Zealand ranging from 52 % to 78 % explained variance for split periods (1901–1950/1951–1995), with equally robust independent validation (coefficient of efficiency = 0.41 to 0.77). Comparison of the Tasmanian BI reconstruction with a quantitative wood anatomical (QWA) reconstruction shows that these parameters record essentially the same strong high-frequency summer temperature signal. Despite these excellent results, a substantial challenge exists with the capture of potential secular-scale climate trends. Although DB, band-pass, and other signal processing methods may help with this issue, substantially more experimentation is needed in conjunction with comparative analysis with ring density and QWA measurements.
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ItemMapping canopy nitrogen-scapes to assess foraging habitat for a vulnerable arboreal folivore in mixed-species Eucalyptus forests(WILEY, 2021-12)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.
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ItemCompound climate extremes driving recent sub-continental tree mortality in northern Australia have no precedent in recent centuries(NATURE PORTFOLIO, 2021-09-15)Compound climate extremes (CCEs) can have significant and persistent environmental impacts on ecosystems. However, knowledge of the occurrence of CCEs beyond the past ~ 50 years, and hence their ecological impacts, is limited. Here, we place the widespread 2015-16 mangrove dieback and the more recent 2020 inland native forest dieback events in northern Australia into a longer historical context using locally relevant palaeoclimate records. Over recent centuries, multiple occurrences of analogous antecedent and coincident climate conditions associated with the mangrove dieback event were identified in this compilation. However, rising sea level-a key antecedent condition-over the three decades prior to the mangrove dieback is unprecedented in the past 220 years. Similarly, dieback in inland forests and savannas was associated with a multi-decadal wetting trend followed by the longest and most intense drought conditions of the past 250 years, coupled with rising temperatures. While many ecological communities may have experienced CCEs in past centuries, the addition of new environmental stressors associated with varying aspects of global change may exceed their thresholds of resilience. Palaeoclimate compilations provide the much-needed longer term context to better assess frequency and changes in some types of CCEs and their environmental impacts.
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ItemDisentangling fire intensity and species' susceptibility to fire in a species-rich seasonal tropical forest(WILEY, 2020-07)Increasing temperatures and human activity are likely to reduce fire return intervals in the seasonal tropics. Anticipating how more frequent fires may alter forest community structure and composition requires understanding how fire intensity and species‐specific responses to fires interact to drive fire‐induced mortality for large numbers of species. We developed an analytical framework to estimate unobserved fire intensities and species‐ and size‐specific susceptibility to fire using observed mortality data. We used census data from a 50‐ha forest dynamics plot in western Thailand to better understand species and community responses to a fire that burned ∼60% of the plot in 2005. Trees species, size and status (live, dead) were censused just before the fire (2004) and again 5 years later (2009). We jointly estimated a map of relative fire intensity and species‐specific size‐dependent background and fire‐induced mortality. We then calculated the time required for individuals of each species to reach a fire‐safe size threshold (the age at which the fire‐induced mortality probability was <50%). To better understand community‐level responses to fire, we compared results among different species groups (canopy status, forest‐type association). Our model‐derived map of fire intensity closely matched the field survey taken in the days after the fire. On average, individuals growing at the 95th percentile growth rate for most species groups required ∼5 years to reach their species’ fire‐safe size threshold, while individuals growing at the median growth rate required ∼17 years (assuming growth <1 cm diameter at breast height was similar to growth >1 cm). However, understorey species associated with the seasonal evergreen forest took 1.8 times longer than average to reach their fire‐safe size threshold, with one species requiring up to 190 years. Synthesis. Our approach provided insights into spatial patterning of fire intensity in a seasonal tropical forest and species‐ and size‐specific susceptibility to fire‐induced mortality. Our results suggest increasing fire frequency will have the greatest impact on slow‐growing understorey species of the evergreen forest. In addition, our model accurately predicts the growing dominance of a fast‐growing understorey species, Croton roxburghii; Euphorbiaceae, common to evergreen and deciduous forests that can reach its fire‐safe size threshold in 1.3 years.
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ItemClimate change drives habitat contraction of a nocturnal arboreal marsupial at its physiological limits(WILEY, 2020-10-01)Increasing impacts of climatic change and anthropogenic disturbances on natural ecosystems are leading to population declines or extinctions of many species worldwide. In Australia, recent climatic change has caused population declines in some native fauna. The projected increase in mean annual temperature by up to 4°C by the end of the 21st century is expected to exacerbate these trends. The greater glider (Petauroides volans), Australia’s largest gliding marsupial, is widely distributed along the eastern coast, but has recently experienced drastic declines in population numbers. Its association with hollow‐bearing trees, used for nesting, has made it an important species for the conservation of old‐growth forest ecosystems. Fires and timber harvesting have been identified as threats to the species. Greater gliders have disappeared however from areas that have experienced neither raising questions about the role of other factors in their decline. A unique physiology and strict Eucalyptus diet make them vulnerable to high temperatures and low water availability. As such, climatic conditions may drive habitat selection and recent climatic trends may be contributing to observed population declines. Using presence:absence data from across its distribution in Victoria, coupled with high spatial and temporal resolution climatic data and machine‐learning modeling, we tested the influence of climatic, topographic, edaphic, biotic, and disturbance variables on greater glider occupancy and habitat suitability. We found that climatic variables, particularly those related to aridity and extreme weather conditions, such as number of nights warmer than 20°C, were highly significant predictors of greater glider occurrence. Climatic conditions associated with habitat suitability have changed over time, with increasing aridity across much of its southeastern distribution. These changes in climate are closely aligned with observed population declines across this region. At higher elevation, some areas where the greater glider is observed at high densities, conditions have become wetter, which is improving habitat quality. These areas are of growing significance to greater glider conservation as they will become increasingly important as climatic refugia in the coming decades. Protecting these areas of habitat will be critical for facilitating the conservation of greater gliders as the broader landscape becomes less hospitable under future climatic change.
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ItemFire as a fundamental ecological process: Research advances and frontiers(WILEY, 2020-06-08)Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire‐dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study. Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above‐ground ecology, (d) fire effects on below‐ground ecology, (e) fire behaviour and (f) fire ecology modelling. We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts. Synthesis: As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives.
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ItemThe effect of species, size, and fire intensity on tree mortality within a catastrophic bushfire complex(WILEY, 2021-09)Infrequent, high-intensity disturbances can have profound impacts on forested landscapes, changing forest structure and altering relative species abundance. However, due to their rarity and the logistical challenges of directly observing such extreme events, both the spatial variability of disturbance intensity and the species-specific responses to this variability are poorly understood. We used observed patterns of mortality across a fire severity gradient following the 2009 Black Saturday fires in southeastern Australia to simultaneously estimate (1) species- and size-specific susceptibility to fire-induced mortality and (2) fire intensity. We found broad variation in patterns of fire susceptibility among the 10 tree species (five eucalypts and five non-eucalypts) sufficiently abundant for analysis. Among the eucalypts, Eucalyptus obliqua was the most resistant to fire-induced mortality, with trees of ~25 cm DBH having a 50% probability of surviving even the most intense fires. In contrast, E. regnans had 100% mortality across all size classes when subjected to high-intensity fire. Basal resprouting occurred in six of the study species and, when accounted for, fundamentally changed the mortality profile of these species, highlighting the importance of resprouting as an adaptation to fire in these landscapes. In particular, the two iconic cool temperate rainforest species (Nothofagus cunninghami and Atherosperma moschatum) were strong resprouters (~45% of individuals were able to resprout after being top-killed by fire). We also found evidence for compositional shifts in regeneration above threshold values of fire intensity in cool temperate rainforest and mixed forest sites, both of which have important conservation values within these landscapes. The observed patterns of species- and size-specific susceptibility to fire-induced mortality may be used to anticipate changes in forest structure and composition in the future. In addition, they may also help guide forest management strategies that reduce the length of time individual trees are exposed to potentially lethal fires, thereby increasing the resilience of these forests to future fires.