Australian Vegetation Research Articles

Rain use efficiency gradients across Australian ecosystems

Rain use efficiency (RUE) quantifies the ecosystem's capacity to use precipitation water to assimilate atmospheric CO2. The spatial distribution of RUE and its drivers across the Australian continent is largely unknown. This knowledge gap limits our understanding of the possible contribution of Australian ecosystems to global carbon assimilation. This study investigates the spatial distribution of RUE across diverse terrestrial ecosystems in Australia. The results show that RUE ranges from 0.43 (1st percentile) to 3.10 (99th percentile) g C m−2 mm−1 with a continental mean of 1.19 g C m−2 mm−1. About 68 % of the spatiotemporal variability of RUE can be explained by a multiple linear regression model primarily contributed by climatic predictors. Benchmarked by the model estimation, drainage-diverging/converging landscapes tend to have reduced/increased RUE. The model also revealed the impact of increasing atmospheric CO2 concentration on RUE. The continental mean RUE would increase by between 29.3 and 64.8 % by the end of this century under the SSP5–8.5 scenario in which the CO2 concentration is projected to double from the present level. This increase in projected RUE is attributed to the assumed greening effect of increasing CO2 concentration, which does not consider the saturation of CO2 fertilisation effect and the warming effect on increasing wildfire occurrence. Under the SSP1–2.6 scenario, RUE would decrease by about 7 %. This study provides baseline RUEs of various ecosystems in Australia for investigating the impacts of human interferences and climate change on the capacity of Australian vegetation to assimilate atmospheric CO2 under given precipitation.

What did it used to look like? A case study from tall, wet mainland Mountain Ash forests prior to British invasion

AbstractThere has been extensive commentary about historical First Nations' land management in Australia, including in tall, wet forests, and therefore their condition at the time of the British invasion in 1788. Popular texts have interpreted records kept by early British invaders to argue that extensive areas of tall, wet forest were kept open through frequent burning by the First Peoples. However, these interpretations conflict with historical and ecological evidence, which is rarely acknowledged in public discourse. Here, we present evidence about what Victorian Mountain Ash (Eucalyptus regnans) forests were like at the time of the British invasion. We show that at the time of the British invasion, most areas of mainland Mountain Ash forests were likely to have been naturally dense and wet, with: (1) overstorey trees spaced relatively widely; and (2) an understorey consisting of a cool temperate rainforest mesic layer. Ecological and physiological evidence suggests that Mountain Ash forests evolved under conditions where high‐severity wildfire was comparatively rare, leading to patterns of landscape‐level cover dominated by relatively mature forests. This is broadly consistent with reports from the First Peoples, early historical accounts, paintings, and photographs. These forests were not open or park‐like, as may have been the case in some other Australian vegetation types. However, these forests were not wilderness, but places of significance to the First Peoples. Understanding forest structure at the time of the British invasion is critically important in establishing historical reference conditions for guiding appropriate restoration programmes, especially the reinstatement of traditional ecological knowledge, after long periods of post‐British invasion disturbance and degradation. Notably, the dense, wet understorey that characterizes Mountain Ash forests should be recognized as an inherent and entirely natural part of the ecological dynamics of this ecosystem, with approaches to thin, burn, or remove it highly likely to be counterproductive and have a range of detrimental environmental effects.

A framework for defining fire danger to support fire management operations in Australia†

Background Development of the Australian Fire Danger Rating System began in 2017 with a project aimed at demonstrating the feasibility of a new fire danger rating system through a Research Prototype (AFDRSRP) that accounted for variability in Australian vegetation types, was nationally applicable, modular and open to continuous improvement. Aims In this manuscript, we identify and define transition points and categories for the AFDRSRP. We discuss user responses to the categorisation during a live trial evaluation of the AFDRSRP and reflect on limitations and potential improvements. Methods A review of available literature, broad consultation with stakeholders and reanalysis of fire impact data were used to determine suitable thresholds for categorising fire danger within the AFDRSRP. Key results Fire danger categories within the AFDRSRP reflect transitions in fire behaviour that result in application of different fire management strategies or are associated with variation in serious consequences and impacts. Conclusions The AFDRSRP incorporated the best available science, supported by a well-defined framework for categorising and defining fire danger making it suitable for application across Australian fire jurisdictions and range of fuel types. Implications The framework allows fire managers to assess the accuracy and appropriateness of forecasted fire danger.

Habitat in flames: How climate change will affect fire risk across koala forests

Aim:Generate fire susceptibility maps for the present and 2070, to identify the threat wildfires pose to koalas now and under future climate change. Location:Australia. Time period:Present and 2070. Major taxa studied:60 main tree species browsed by koalas. Method:The Decision Tree machine learning algorithm was applied to generate a fire susceptibility index (a measure of the potential for a given area or region to experience wildfires) using a dataset of conditioning factors, namely: altitude, aspect, rainfall, distance from rivers, distance from roads, forest type, geology, koala presence and future dietary sources, land use-land cover (LULC), normalized difference vegetation index (NDVI), slope, soil, temperature, and wind speed. Results:We found a general increase in susceptibility of Australian vegetation to bushfires overall. The simulation for current conditions indicated that 39.56% of total koala habitat has a fire susceptibility rating of “very high” or “high”, increasing to 44.61% by 2070. Main conclusions:Wildfires will increasingly impact koala populations in the future. If this iconic and vulnerable marsupial is to be protected, conservation strategies need to be adapted to deal with this threat. It is crucial to strike a balance between ensuring that koala habitats and populations are not completely destroyed by fire while also allowing for forest rejuvenation and regeneration through periodic burns.

Patterns and drivers of plant diversity across Australia

Biodiversity analyses across continental extents are important in providing comprehensive information on patterns and likely drivers of diversity. For vascular plants in Australia, community‐level diversity analyses have been restricted by the lack of a consistent plot‐based survey dataset across the continent. To overcome these challenges, we collated and harmonised plot‐based vegetation survey data from the major data sources across Australia and used them as the basis for modelling species richness (α‐diversity) and community compositional dissimilarity (β‐diversity), standardised to 400 m2, with the aim of mapping diversity patterns and identifying potential environmental drivers. The harmonised Australian vegetation plot (HAVPlot) dataset includes 219 552 plots, of which we used 115 083 to analyse plant diversity. Models of species richness and compositional dissimilarity both explained approximately one‐third of the variation in plant diversity across Australia (D2 = 33.0% and 32.7%, respectively). The strongest environmental predictors for both aspects of diversity were a combination of temperature and precipitation, with soil texture and topographic heterogeneity also important. The fine‐resolution (≈ 90 m) spatial predictions of species richness and compositional dissimilarity identify areas expected to be of particular importance for plant diversity, including south‐western Australia, rainforests of eastern Australia and the Australian Alps. Arid areas of central and western Australia are predicted to support assemblages that are less speciose or unique; however, these areas are most in need of additional survey data to fill the spatial, environmental and taxonomic gaps in the HAVPlot dataset. The harmonised data and model predictions presented here provide new insight into plant diversity patterns across Australia, enabling a wide variety of future research, such as exploring changes in species abundances, linking compositional patterns to functional traits or undertaking conservation assessments for selected components of the flora.

Carbon dioxide and particulate emissions from the 2013 Tasmanian firestorm: implications for Australian carbon accounting

BackgroundUncontrolled wildfires in Australian temperate Eucalyptus forests produce significant smoke emissions, particularly carbon dioxide (CO2) and particulates. Emissions from fires in these ecosystems, however, have received less research attention than the fires in North American conifer forests or frequently burned Australian tropical savannas. Here, we use the 2013 Forcett–Dunalley fire that caused the first recorded pyrocumulonimbus event in Tasmania, to understand CO2 and particulate matter (PM2.5) emissions from a severe Eucalyptus forest fire. We investigate the spatial patterns of the two emissions using a fine scale mapping of vegetation and fire severity (50 m resolution), and utilising available emission factors suitable for Australian vegetation types. We compare the results with coarse-scale (28 km resolution) emissions estimates from Global Fire Emissions Database (GFED) to determine the reliability of the global model in emissions estimation.ResultsThe fine scale inventory yielded total CO2 emission of 1.125 ± 0.232 Tg and PM2.5 emission of 0.022 ± 0.006 Tg, representing a loss of 56 t CO2 ha−1 and 1 t PM2.5 ha−1. The CO2 emissions were comparable to GFED estimates, but GFED PM2.5 estimates were lower by a factor of three. This study highlights the reliability of GFED for CO2 but not PM2.5 for estimating emissions from Eucalyptus forest fires. Our fine scale and GFED estimates showed that the Forcett–Dunalley fire produced 30% of 2013 fire carbon emissions in Tasmania, and 26–36% of mean annual fire emissions for the State, representing a significant single source of emissions.ConclusionsOur analyses highlight the need for improved PM2.5 emission factors specific to Australian vegetation, and better characterisation of fuel loads, particularly coarse fuel loads, to quantify wildfire particulate and greenhouse gas emissions more accurately. Current Australian carbon accountancy approach of excluding large wildfires from final GHG accounts likely exaggerates Tasmania’s claim to carbon neutrality; we therefore recommend that planned and unplanned emissions are included in the final national and state greenhouse gas accounting to international conventions. Advancing these issues is important given the trajectory of more frequent large fires driven by anthropogenic climate change.

Megafire‐induced interval squeeze threatens vegetation at landscape scales

Wildfires in 2019–2020 broke global records for extent and severity, affirming the arrival of the megafire era. Frequent megafires reflect changes to fire regimes that can negatively impact species and ecosystems. Here, we offer what we believe to be the first comprehensive analysis of megafire impacts on southeastern Australian vegetation communities, combining remote‐sensing data, fire‐history records, and plant trait‐derived fire interval thresholds. In our study area, fires burned over 5.5 million ha. We found that one‐third of all native vegetation in this region has burned too frequently following the megafires, particularly impacting fire‐sensitive vegetation (for example, rainforests). This represents a single‐year increase of 36% in the vegetation at risk of interval squeeze (vegetation transitions driven by altered fire regimes) compared to the previous 59 years combined. We demonstrate that megafires can overrun recently burned vegetation and infiltrate refugia, reducing fire intervals beyond the persistence thresholds of plant species and increasing the risk of ecosystem collapse. Averting this will require innovative approaches to fire management. However, if climate change is not addressed, ecosystem collapse may be unavoidable especially for ecosystems adapted to infrequent, high‐severity fire.

Environmental associations of abundance-weighted functional traits in Australian plant communities

Predictions of how vegetation responds to spatial and temporal differences in climate rely on established links with plant functional traits and vegetation types that can be encoded into Dynamic Global Vegetation Models. Individual traits have been linked to climate at species level and at community level within regions. However, a recent global assessment of aggregated community level traits found unexpectedly weak links with macroclimate, bringing into question broadscale trait–climate associations and implicating local-scale environmental differences in the filtering of communities. To further evaluate patterns in light of these somewhat contradictory results, we quantified the power of macro-environmental variables to explain aggregated plant community traits, taking advantage of new trait data for leaf area, plant height and seed mass combined with a national survey that records cover-abundance using consistent methods for a large number of plots across Australia. In contrast to the global study, we found that abundance-weighted community mean and variance of leaf area and maximum height were correlated with macroclimate. Height and leaf area were highest in wet (especially warm, wet) environments, with actual evapotranspiration explaining 30% of variation in leaf area and 26% in maximum height. Seed mass was weakly related to environment, with no variable explaining more than 5% of variance. Considering all three traits together in a redundancy analysis, the complete set of environmental variables explained 43% of variation in site-mean traits and 29% of within-site trait variance. While significant trait variation remains unexplained, the trait–environment relationships reported here suggest climatically-driven filtering plays a strong role in assembling these vegetation communities. Regional assessments using standardised species abundances can therefore be used to predict aspects of vegetation function. Our quantification of plant community trait patterns along macroclimatic gradients at continental scale thereby contributes a much-needed functional basis for Australian vegetation.

The Role of Heat Flux in an Idealised Firebreak Built in Surface and Crown Fires

The disruptions to wildland fires, such as firebreaks, roads and rivers, can limit the spread of wildfire propagating through surface or crown fire. A large forest can be separated into different zones by carefully constructing firebreaks through modification of vegetation in firebreak regions. However, the wildland fire behaviour can be unpredictable due to the presence of either wind- or buoyancy-driven flow in the fire. In this study, we aim to test the efficacy of an idealised firebreak constructed by unburned vegetation. The physics-based large eddy simulation (LES) simulation is conducted using Wildland–urban interface Fire Dynamic Simulator (WFDS). We have carefully chosen different wind velocities with low to high values, 2.5~12.5 m/s, so the different fire behaviours can be studied. The behaviour of surface fire is studied by Australian grassland vegetation, while the crown fire is represented by placing cone-shaped trees with grass underneath. With varying velocity and vegetation, four values of firebreak widths (Lc), ranging from 5~20 m, is tested for successful break distance needed for the firebreak. For each failure or successful firebreak width, we have assessed the characteristics of fire intensity, mechanism of heat transfer, heat flux, and surface temperature. It was found that with the inclusion of forest trees, the heat release rate (HRR) increased substantially due to greater amount of fuel involved. The non-dimensional Byram’s convective number (NC) was calculated, which justifies simulated heat flux and fire characteristics. For each case, HRR, total heat fluxes, total preheat flux, total preheat radiation and convective heat flux, surface temperature and fire propagation mode are presented in the details. Some threshold heat flux was observed on the far side of the firebreak and further studies are needed to identify them conclusively.

Removal of particulate air pollutants by Australian vegetation potentially used for green barriers

Urban air quality monitoring and control are becoming increasingly important as the amount of airborne pollutants is directly related to public health. One of the main strategies to improve air quality is to increase the number of plants per unit land surface area across cities through urban greening. In addition to the process of photosynthesis, which minimizes the content of harmful gas impurities into the atmosphere, the planting of relevant vegetation in the form of high-density street vegetation, green walls or green façades, acts as a barrier to the passage of atmospheric aerosol particles into crowded areas. Depending on the availability of local plants, various design strategies could be used to minimise air pollution and achieve maximum air quality. On this basis, it is important to investigate filtration capabilities of a range of locally available plants enabling landscape architects to design the most cost-effective green barriers in various countries. Four common representatives of Australian flora have been selected and tested in this study as promising candidates. A number of configuration scenarios involving manipulation of a layer thickness and biomass packing were tested as potential filters for collection of aerosols sizing from 0.5 μm diameter. The results showed that the plant materials were highly efficient in filtering coarse particles (≥2.5 μm), with efficiencies ranging from 50.1% to 99.9%. The smaller particle sizes were filtered with comparatively lower efficiencies, ranging from 0.6% to 51.3% and 8.6%–79.1% for particles of 0.5 μm and 1 μm diameter respectively. Optimal scenarios were proposed and discussed.

High fire frequency and the impact of the 2019–2020 megafires on Australian plant diversity

AbstractAimTo quantify the impact of the 2019–2020 megafires on Australian plant diversity by assessing burnt area across 26,062 species ranges and the effects of fire history on recovery potential. Further, to exemplify a strategic approach to prioritizing plant species affected by fire for recovery actions and conservation planning at a national scale.LocationAustralia.MethodsWe combine data on geographic range, fire extent, response traits and fire history to assess the proportion of species ranges burnt in both the 2019–2020 fires and the past.ResultsAcross Australia, suitable habitat for 69% of all plant species was burnt (17,197 species) by the 2019–2020 fires and herbarium specimens confirm the presence of 9,092 of these species across the fire extent since 1950. Burnt ranges include those of 587 plants listed as threatened under national legislation (44% of Australia's threatened plants). A total of 3,998 of the 17,197 fire‐affected species are known to resprout after fire, but at least 2,928 must complete their entire life cycle—from germinant to reproducing adult—prior to subsequent fires, as they are killed by fire. Data on previous fires show that, for 257 species, the historical intervals between fire events across their range are likely too short to allow regeneration. For a further 411 species, future fires during recovery will increase extinction risk as current populations are dominated by immature individuals.Main conclusionMany Australian plant species have strategies to persist under certain fire regimes, and will recover given time, suitable conditions and low exposure to threats. However, short fire intervals both before and after the 2019–2020 fire season pose a serious risk to the recovery of at least 595 species. Persistent knowledge gaps about species fire response and post‐fire population persistence threaten the effective long‐term management of Australian vegetation in an increasingly pyric world.

Implications of the 2019\u20132020 megafires for the biogeography and conservation of Australian vegetation

Australia’s 2019–2020 ‘Black Summer’ bushfires burnt more than 8 million hectares of vegetation across the south-east of the continent, an event unprecedented in the last 200 years. Here we report the impacts of these fires on vascular plant species and communities. Using a map of the fires generated from remotely sensed hotspot data we show that, across 11 Australian bioregions, 17 major native vegetation groups were severely burnt, and up to 67–83% of globally significant rainforests and eucalypt forests and woodlands. Based on geocoded species occurrence data we estimate that >50% of known populations or ranges of 816 native vascular plant species were burnt during the fires, including more than 100 species with geographic ranges more than 500 km across. Habitat and fire response data show that most affected species are resilient to fire. However, the massive biogeographic, demographic and taxonomic breadth of impacts of the 2019–2020 fires may leave some ecosystems, particularly relictual Gondwanan rainforests, susceptible to regeneration failure and landscape-scale decline.

Australian vegetation classification and the International Vegetation Classification framework: an overview with case studies

Recent advances in conceptual frameworks in vegetation classifications, such as the EcoVeg approach that underpins the International Vegetation Classification (IVC) developed by NatureServe staff and colleagues, offer opportunities to enhance national classification initiatives. National level initiatives provide an important stepping-stone between international units and subnational units. Australia has a long history of developing various vegetation typologies at local to regional scales, but ecologists recognise the need for an Australia-wide, plot-based vegetation classification system that incorporates the principles of the EcoVeg approach, and thereby helps build an international classification system. Using two case studies, we provide a comparison of various structures and criteria for relevant Australian classifications in the context of the IVC, and exemplify how Australian classifications of forest, shrublands, grasslands, and deserts could potentially link into the IVC hierarchy to illustrate the capacity of the IVC to summarise the full range of Australian vegetation at a broad formation (biome) scale. We then discuss how the IVC might inform future work towards an Australian vegetation classification system and, vice versa, the implications of an Australian vegetation classification for IVC development.

Potential benefits of biodiversity to Australian vegetation projects registered with the Emissions Reduction Fund—is there a carbon‐biodiversity trade‐off?

SummaryGlobal assessments show biodiversity has already declined beyond ‘safe limits’ across most biomes, calling for large‐scale conservation and restoration interventions. At the same time, the potential and emerging catastrophic impacts of accelerated climate change have led to increasing investment in climate change mitigation efforts through maintaining or sequestering carbon in vegetation biomass, particularly woodlands and forests. This raises the challenge of whether these climate change mitigation investments can concurrently contribute to ameliorating the biodiversity crisis. However, the assumption of industry observers is that tree monocultures will sequester more carbon than biodiverse plantings, that is, there is a carbon‐biodiversity trade‐off. Here, we review experimental and observational evidence to examine whether a biodiversity trade‐off is necessary to maximise carbon credits. We apply the findings to the four types of Australian vegetation projects that have been registered with the Australian Government’s Emissions Reduction Fund since 2012: avoided deforestation, managed regeneration, farm forestry and tree planting. We find limited evidence in the biodiversity‐ecosystem function literature for a trade‐off between biodiversity and carbon stored in above‐ground vegetation biomass; rather we find evidence for neutral or positive relationships. Further, additional benefits of plant diversity to carbon storage, rarely accounted for in vegetation projects, include increased soil carbon storage, stability and ecological resilience to disturbances. Our findings suggest opportunities for enhancing biodiversity in vegetation projects, for example through more diverse plantings, or manipulation of herbivores or plant propagules in avoided deforestation and managed regeneration projects. More research is needed to understand the contribution of faunal diversity to ecosystem functions and to manage fire in vegetation projects. We conclude that vegetation projects can aim to benefit biodiversity without compromising carbon credits.

Identifying areas at risk of drought-induced tree mortality across South-Eastern Australia.

South-East Australia has recently been subjected to two of the worst droughts in the historical record (Millennium Drought, 2000-2009 and Big Dry, 2017-2019). Unfortunately, a lack of forest monitoring has made it difficult to determine whether widespread tree mortality has resulted from these droughts. Anecdotal observations suggest the Big Dry may have led to more significant tree mortality than the Millennium drought. Critically, to be able to robustly project future expected climate change effects on Australian vegetation, we need to assess the vulnerability of Australian trees to drought. Here we implemented a model of plant hydraulics into the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model. We parameterized the drought response behaviour of five broad vegetation types, based on a common garden dry-down experiment with species originating across a rainfall gradient (188-1,125mm/year) across South-East Australia. The new hydraulics model significantly improved (~35%-45% reduction in root mean square error) CABLE's previous predictions of latent heat fluxes during periods of water stress at two eddy covariance sites in Australia. Landscape-scale predictions of the greatest percentage loss of hydraulic conductivity (PLC) of about 40%-60%, were broadly consistent with satellite estimates of regions of the greatest change in both droughts. In neither drought did CABLE predict that trees would have reached critical PLC in widespread areas (i.e.it projected a low mortality risk), although the model highlighted critical levels near the desert regions of South-East Australia where few trees live. Overall, our experimentally constrained model results imply significant resilience to drought conferred by hydraulic function, but also highlight critical data and scientific gaps. Our approach presents a promising avenue to integrate experimental data and make regional-scale predictions of potential drought-induced hydraulic failure.

Does irrigation cooling effect intensify during heatwaves? A case study in the Melbourne botanic gardens

Reducing night-time air temperature by irrigating urban greenery can ameliorate heat stress in cities. Past studies often used modelling approaches to investigate the irrigation cooling effect during heatwaves. However, few observational studies have compared the differences in micro-scale irrigation cooling effect between heatwave and non-heatwave conditions. This study examines whether nocturnal irrigation cooling effects intensify during heatwaves, as there have been conflicting results in the literature regarding this issue. During the Australian summer of December 2013 to March 2014, this study was conducted in the Royal Botanic Gardens Victoria’s Melbourne Gardens (mixture of Australian and exotic vegetation) and in the Australian Gardens of its Cranbourne Gardens (specialises in Australian vegetation). We used the excess heat factor (EHF) to identify one severe heatwave (EHF = 34.9) and one extreme heatwave (EHF = 155.6) in our study period. Using meteorological observations, irrigation data and one-way ANOVA, we present the differences in cooling associated with irrigation between different types of landscape in the two gardens. During non-heatwave conditions, there was 0.5 °C – 1 °C of cooling associated with overnight irrigation of 20–25 mm. During heatwave conditions, several lawn areas recorded greater cooling (2 °C – 4 °C) associated with irrigation of similar amounts, but this phenomenon was not observed in areas dominated by hard surfaces. The magnitude and timing of the irrigation cooling effects also differed in various garden sites, with residual cooling effects observed lasting for several hours in certain sites following nocturnal irrigation events. Our results suggest that some significant cooling at the micro-scale is apparent from irrigated landscape in Melbourne, which has a temperate oceanic climate with occasional heatwaves. Moreover, the irrigation cooling effect in the Melbourne Gardens intensifies during heatwaves. Our findings could inform landscape succession planning to prepare for a hotter future climate.

Emissions of gaseous pollutants from laboratory-based fires of vegetation from five common vegetation types in Western Australia

This study investigated emission factors (EFs) for CO2, CO, NO and carbonyls from laboratory-based combustion of five typical vegetation types of Western Australia. A range of combustion conditions was obtained by controlling the vegetation moisture content and air flow rate. CO2, CO and NO were measured using a multi-gas monitor MultiRAE. Six carbonyls were collected using 2,4-DNPH sorbent tubes and analysed using HPLC-UV.Burns of woodland (Banksia) and forest (Jarrah) had significantly higher EFCO, with lower modified combustion efficiency (MCE) than those of tropical grass (Spinifex). Temperate grass (Veldt) fires had lower EFCO2 and higher EFCO and EFcarbonyls, and a much lower MCE than those of the tropical grass fires. EFNO were similar for woodland, forest and tropical grass but large differences in EFNO were observed for Spinifex and Veldt grass. Formaldehyde was the most abundant carbonyl emitted.Combustion conditions influenced the EFcarbonyls with larger EFs from burns with higher fuel moisture contents and/or at higher flow rates. Functions to extrapolate EFs for infrequently measured carbonyls (acetaldehyde, acetone and propionaldehyde) from EFformaldehyde were developed. The EFCO2 and EFCO were similar to values reported from field measurements for similar ecosystems in Australia, indicating the applicability of these laboratory-based results. EFs for other gases differed to those reported from bushfires in other parts of the world suggesting that to improve prediction of bushfire emissions and impacts in Australia, EFs of all fire-prone Australian vegetation types should be determined, particularly for those in close proximity to densely populated areas.

Drought Impacts on Australian Vegetation During the Millennium Drought Measured With Multisource Spaceborne Remote Sensing

AbstractDuring the period from 1997 to 2009, Australia experienced a severe and persistent drought known as the millennium drought (MD). Major water shortages were reported across the continent, and there were some field accounts of tree mortality and dieback, but large‐area assessment has been lacking. Given uncertain projections of future drought conditions in South‐East Australia, analysis of the MD presents a valuable opportunity to assess possible impacts of these future trends. In this study, we analyzed the magnitude and sensitivity of vegetation responses to the MD with satellite‐derived information including the fraction of photosynthetically absorbed radiation, photosynthetic vegetation cover, canopy density derived from vegetation optical depth, and aboveground biomass carbon. Results show that the most severe impacts were concentrated in southeastern Australia where all four biophysical variables exhibited the highest absolute declines. Cultivated lands, followed by grasslands, experienced the largest drought impact and also demonstrated the highest sensitivity to drought compared to natural biomes. Shrublands showed the greatest resistance to drought‐induced declines. Forests exhibited the lowest sensitivity in canopy properties but average drought sensitivity for biomass, similar to other natural biomes. More arid settings tended to have higher drought sensitivity for canopy properties but lower sensitivity to biomass loss. Drought‐induced carbon releases were largest in forested ecosystems and in more humid climatic settings. High sensitivity of forest biomass to drought suggests that a large amount of carbon could be vulnerable to release to the atmosphere.

Long term impacts of Phytophthora cinnamomi infestation on heathy woodland in the Great Otway National Park in south-eastern Australia

The significant impacts of the introduced plant pathogen Phytophthora cinnamomi on native Australian vegetation have been well documented, but there is less knowledge of long-term effects. We assessed long-term (26 years) disease progression and impacts on vegetation floristics and structure at a heathy woodland site in the Great Otway National Park, eastern section. Disease progressed dramatically between 1989 and 2005 and by 2015 only 0.08% of the site was non-diseased. There were significant declines in plant species richness and numbers of susceptible species; and increases in percentage cover of resistant sedges and grasses overall, and in cover of Leptospermum continentale (prickly tea-tree) in post-disease areas. There were significant declines of Xanthorrhoea australis (Austral grass-tree), a keystone species that contributes greatly to vegetation structure and fauna habitat. There is an urgent need to map the distribution of P. cinnamomi affected vegetation and identify floristically important non-diseased vegetation in the national park. It is imperative that quarantine of non-infested areas, phosphite application, track closures and vehicle wash-downs be implemented to reduce disease extension and protect the significant biodiversity of the region including species rich heathlands and nationally listed threatened plant and fauna species and their habitats.

Anatomical aspects of xeromorphy in arid-adapted plants of Australia

Plants from arid environments have some of the most diverse morphological and anatomical modifications of any terrestrial plants. Most perennials are classified as xerophytes, and have structures that limit water loss during dry weather, provide structural support to help prevent cell collapse during dry periods or store water in photosynthetic tissues. Some of these traits are also found in sclerophyllous plants and traits that may have developed due to evolution of taxa on nutrient poor soils may also benefit the plants under arid conditions. We examined the morpho-anatomical features of photosynthetic organs of three tree and four shrub species with reduced leaves or photosynthetic stems that occur in arid or semiarid sites in Australia to see if there were patterns of tissue formation particularly associated with xeromorphy. In addition, we reviewed information on succulent and resurrection species. In the tree species (Callitris spp.) with decurrent leaves clothing the stems, the close association between the water transport system and stomata, along with anisotropic physiology would allow the species to fix carbon under increasingly dry conditions in contrast to more broad-leaved species. The shrub species (Tetratheca species and Glischrocaryon flavescens) with photosynthetic stems had extensive sclerenchyma and very dense chlorenchyma. The lack of major anatomical differences between leafless species of Tetratheca from arid areas compared with more mesic sites indicates that quite extreme morphological modifications may not exclude species from growing successfully in competition with species from less arid areas. The sclerophyll flora now characteristic of Australian vegetation from seasonally arid climates may have evolved during mesic times in the past but with relatively minor modifications was able to adjust to the gradually drying climate of much of Australia up to the present time.