School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemShort-interval, high-severity wildfires cause declines in soil seed bank diversity in montane forests of south-eastern Australia(Elsevier, 2024-02-01)Wildfires in forested ecosystems are increasing in severity and extent. The adaptations many plants have acquired in response to their natural fire regime may not be sufficient to allow some species to persist. This could impact the forest understorey and its seed bank, which are vital reservoirs of biodiversity, and forest resilience in the face of global change. We present a case study of the montane forests of south-eastern Australia, an area subjected to an increase in frequency and severity of fires. We utilise field surveys and a soil seed bank germination study to investigate if short-interval, high-severity wildfires affect the understorey diversity in montane forests, and if the extant vegetation and the soil seed bank exhibit contrasting responses. We consider species diversity and plant functional traits to explore plant diversity in long unburned sites, and sites with one, two or three short-interval, high-severity fires in the past 25 years. With increasing fire frequency, we found a decrease in total species richness, Shannon's diversity, and the richness of resprouters in the soil seed bank, contrasting a lack of response in the extant vegetation. Increased fire frequency shifted the species composition and the frequency of plant functional groups of both extant vegetation and soil seed bank towards a decrease in clonal resprouters and increase in grasses and other upright herbs. The frequency of wind-dispersed perennials and short-lived seeders and exotics increased sharply following single high severity burn, particularly in the soil seed bank, and remained elevated relative to long unburnt with subsequent fire. The combined species (extant vegetation plus soil seed bank) pool mirrored shifts in the frequency of functional groups in extant vegetation and soil seed bank. These findings highlight the importance of considering the soil seed bank when examining the effects of fire on fire-prone forests. Although a lack of response in the extant vegetation may be a buffering effect of the soil seed bank, the shift in the frequency of plant functional groups in the combined species pool suggests this cannot be maintained indefinitely. The increase in frequency and abundance of species characteristic of early successional states has implications for increased flammability and potential positive feedbacks between past fire and future fire, especially in a warming and drying climate. These shifts were independent of the fire response strategy of eucalypt canopy species raising significant questions of whether artificial re-seeding programs should extend beyond the current focus on obligate seeding forests and an obligate seeding tree.
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ItemNo Preview AvailableCanopy Composition and Spatial Configuration Influences Beta Diversity in Temperate Regrowth Forests of Southeastern Australia(MDPI, 2023-03)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.
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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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ItemPapua at the Crossroads: A Plea for Systematic Conservation Planning in One of the Largest Remaining Areas of Tropical Rainforest(FRONTIERS MEDIA SA, 2022-02-11)Land-use change has progressed rapidly throughout the Indonesian archipelago and is now intruding into western New Guinea (Tanah Papua), one of the world’s last wilderness areas with extensive tracts of pristine and highly diverse tropical rainforests. Tanah Papua has reached a crossroads between accelerating environmental degradation and sustainable development policies entailing landscape-scale conservation targets, pledged in the Manokwari Declaration. We assessed the representation of ecoregions and elevational zones within Tanah Papua’s protected area network to identify its shortcomings at broad spatial scales. Lowland ecoregions are less protected than mountainous regions, with half of the western and southern lowlands designated for land-use concessions. Under the direct threat from land-use change, the political motivation in Tanah Papua toward conservation- and culture-centered land management provides a window of opportunity for scientifically guided, proactive conservation planning that integrates sustainable development for the benefit of Indigenous communities.
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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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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.