Semi-arid Regions Of Australia Research Articles

Bathymetric modelling for long-term monitoring of water dynamics of Ramsar-listed lakes using inundation frequency and photon-counting LiDAR data

Accurate information on lake bathymetry and water dynamics is crucial for comprehending the intricate ecological processes in wetland ecosystems, which in turn can inform effective conservation and management strategies. However, obtaining such information can be challenging, particularly in remote areas with limited data. This study presents a way to leverage inundation frequency and ICESat-2 photon-counting LiDAR data to develop bathymetric models for Ramsar-listed lakes in a semi-arid region of Australia. Based on developed bathymetric models, monthly time series of water areas, levels and volumes were derived, providing a long-term view of the water dynamics of the two lakes from1987-2021. This is the first time that such detailed bathymetry and long-term water dynamics have been established for Ramsar-listed lakes in Australia's Outback. The findings of this study provide the most up-to-date information on the long-term trends of the Ramsar-listed lakes in the region and highlight the lakes’ prolonged dry spells when drought conditions prevailed through much of the 2000s and the 2010s as denoted by rainfall deficiencies and high evaporation. The outcome of this study serves as a valuable baseline for understanding the historical and ongoing status of these Ramsar-listed lakes in a warming and drying climate and contributes to the development of strategic plans to fulfill international obligations for wetland protection under the Ramsar Convention.

The Regional Diagnosis of Onset and Demise of the Rainy Season over Tropical and Subtropical Australia

Abstract In this paper, we introduce a novel strategy to robustly diagnose the onset and demise of the rainy season using daily observed rainfall over seven specific regions across Australia, as demarcated by the Natural Resource Management (NRM) agency of Australia. The methodology lies in developing an ensemble spread of the diagnosed onset and demise from randomly perturbing the observed daily time series of rainfall at synoptic scales to obtain a measure of the uncertainty of the diagnosis. Our results indicate that the spread of the ensemble in the diagnosis of the onset and demise dates of the rainy season is higher in the subtropical region than the tropical region. Secular change of earlier onset, later demise, longer length, and wetter season are also identified in many of these regions. The influence of the PDO at decadal scale, ENSO and Indian Ocean dipole at interannual scale, and MJO at intraseasonal scale also reveals significant influence on the evolution of the rainy season over these regions in Australia. Most important, the covariability of the onset date with the length of the season and seasonal rainfall anomaly of the season is highlighted as a valuable relationship that can be exploited for real-time monitoring and providing an outlook of the forthcoming rainy season, which could serve some of the NRM regions. Significance Statement We document the rainfall variability during the rainy season over tropical, subtropical, and semiarid regions of Australia and relate them to modes of climate variability spanning from intraseasonal to secular time scales. The study highlights the varied influence of the modes of climate variability on various aspects of the evolution of the rainy season, such as its onset and demise dates and the seasonal rainfall anomaly over these Australian regions. The study uses 114 years of data and shows that the variations in the length of the rainy season and its seasonal rainfall anomaly are strongly dictated by variations of rainy-season onset date. This provides a quick seasonal outlook of the forthcoming rainy season by just monitoring the onset-date evolution in these regions.

Demonstrating the potential of amberat middens for understanding late Quaternary palaeoenvironments in the Central Pilbara, western Australia

The Pilbara region in Western Australia (WA) is of high biological and archaeological significance, though our understanding of its environmental history is limited. Potentially valuable palaeoenvironmental archives exist throughout the Central Pilbara in caves and rockshelters in the form of amberat middens (crystallised animal urine), which are known from elsewhere to preserve botanical and faunal remains. Here we report a pilot study aimed at assessing how a multiproxy analysis of these middens could be used to infer past environmental change in response to climate change and therefore help to characterise the nature of past human-environmental relationships in the Pilbara region. Findings show that rockshelters of the inland Pilbara contain some of the oldest known amberat middens in Australia, extending fully back to the Last Glacial Maximum (LGM). Well preserved pollen and macrofossils in the middens tentatively suggest that vegetation throughout the late Pleistocene was likely dominated by an open woodland with a shift after 6000 BP to a more heterogenous pattern of vegetation with the increasing dominance of grassland communities. Several hiatuses in midden accumulation are apparent, which are tentatively interpreted as indicating that the region was affected by prolonged dry periods in the past. This may help explain concomitant patterns of decreased human occupation in the corresponding archaeological record. This pilot study has demonstrated the value of amberat middens for providing much needed local paleoenvironmental data in arid and semi-arid regions of Australia.

A comparison of methods for monitoring a sparse population of the red fox (Vulpes vulpes) subject to lethal control using GPS telemetry, camera traps and sand plots

Context The introduced red fox has driven the decline or extinction of numerous wildlife species in Australia, yet little information exists on the population densities of foxes in most ecosystems. Fox monitoring programs will differ widely depending on the goals of management, which, in turn, will determine whether the appropriate metric is a density estimate, or some proxy thereof, and the time and resources required. Aims This study aims to assist wildlife managers to design fit-for-purpose monitoring programs for foxes by providing a better understanding of the utility and precision of various monitoring methods. Methods We surveyed foxes monthly over four consecutive years in a semi-arid region of Australia by using sand plots, camera traps and GPS telemetry. The resultant data were used to produce population estimates from one count-based method, two spatially explicit methods, and two activity indices. Key results The incorporation of GPS-collar data into the spatial capture–recapture approaches greatly reduced uncertainty in estimates of abundance. Activity indices from sand plots were generally higher and more variable than were indices derived from camera traps, whereas estimates from N-mixture models appeared to be biased high. Conclusions Our study indicated that the Allen–Engeman index derived from camera-trap data provided an accurate reflection of change in the underlying fox density, even as density declined towards zero following introduction of lethal control. This method provides an efficient means to detect large shifts in abundance, whether up or down, which may trigger a change to more laborious, but precise, population monitoring methods. If accuracy is paramount (e.g. for reintroduction programs) spatially explicit methods augmented with GPS data provide robust estimates, albeit at a greater cost in resources and expertise than does an index. Implications Our study demonstrated that the shorter the survey period is, the greater is the likelihood that foxes are present but not detected. As such, if limited resources are available, longer monitoring periods conducted less frequently will provide a more accurate reflection of the underlying fox population than do shorter monitoring periods conducted more often.

Increased temperature reduces walnut pollen germination in semi-arid regions of Australia

Increased temperature reduces walnut pollen germination in semi-arid regions of Australia

Temporal Changes in Land Surface Coupling Strength: An Example in a Semi-Arid Region of Australia

AbstractOne of the critical components in understanding the climate system is the interaction between the land and the atmosphere. Whereas previous studies on land–atmosphere coupling mostly focus on its spatial hotspots, we explore the temporal evolution of land surface coupling strength (LCS) during a large-scale flood event in a semiarid region in northern Australia. The LCS indicates the relationship between soil moisture and latent heat flux, and the spatiotemporal variability in precipitation and soil water strongly affects the variability of LCS. The LCS is usually positive in the semiarid climate, where evapotranspiration (ET) occurs under the soil moisture–limited regime and thus increases with soil moisture. However, our analyses of combined land surface modeling and observational datasets show high temporal variability of LCS in the course of the extreme flood event followed by a drying period. The wet regions transferred the ET regime from the soil moisture–limited to the transition section, weakening the linear growth of ET with soil moisture, which resulted in the decline of LCS. The LCS remained weak until the flood retreated and the soil water approached the prestorm average state. Such temporal variation of the LCS has important implications for realistic parameterization of the land–atmosphere coupling and consequently improving subseasonal to seasonal climate forecast.

Space-time monitoring of soil organic carbon content across a semi-arid region of Australia

Monitoring and mapping organic carbon throughout the soil profile is an important task, as land management and fluctuations in rainfall patterns have the potential to substantially alter the levels of soil organic carbon (SOC). This study aims to monitor the change in SOC content between 2002 and 2015 in a semi-arid, irrigated cotton-growing region in Australia under various land uses. One multivariate linear mixed model (MLMM) was used to model SOC content with four response variables – at two sampling depths (0–0.1, and 0.3–0.5 m), and two time points (2002 and 2015). This involved a four-dimensional model (horizontal and vertical space, and time) to monitor the spatio-temporal shifts of SOC content. Such a model utilises the correlation between the four measurements of SOC at the different depths and times. When tested with leave-one-site-out cross-validation, SOC content was predicted with a Lin's concordance correlation coefficient (LCCC) of 0.68, and a root mean square error (RMSE) of 0.21%. The MLMMs produced coherent soil maps, and an ability to detect statistically significant change in SOC content over time. While no change in subsoil (0.3–0.5 m) SOC content was observed across the study area, a small section of the study area revealed a statistically significant increase in SOC content in the topsoil (0–0.1 m). It was not completely clear whether this change was a function of land management, or the extended wet period from 2010 to 2012. The ability of MLMMs to take advantage of the relationship between different soil properties, soil depths, and time points, makes them advantageous for spatio-temporally monitoring soil.

Mapping groundwater potential zones using remote sensing and geographical information systems in a fractured rock setting, Southern Flinders Ranges, South Australia

In Australia, water resource management is a major socio-economic and environmental issue and an essential component of progress. This is more acute in arid and semi-arid regions of Australia. The Southern Flinders Ranges townships of Quorn and Hawker in common with much of the Flinders Ranges suffers from a lack of reliable data to help water resource managers. This paper discusses the delineation and assessment of groundwater potential zones using remote sensing and geospatial techniques in the region, using multi-criteria analyses. The study integrates many thematic layers (rainfall, lithology, lineament density, topographic wetness, slope and aspect) in a GIS environment in order to identify groundwater potential zones. Weights are assigned to class attributes within and between each thematic data layer using an Analytical Hierarchy Process based on the relative importance of each layer. The weighted thematic data layers are then combined to produce a probability of groundwater potential zone map of each study area. The groundwater potential zones were verified with available water data, and showed consistency with the interpretations.

Satellite and ground-based measurements of XCO<sub>2</sub> in a remote semiarid region of Australia

Abstract. In this study, we present ground-based measurements of column-averaged dry-air mole fractions (DMFs) of CO2 (or XCO2) taken in a semiarid region of Australia with an EM27/SUN portable spectrometer equipped with an automated clamshell cover. We compared these measurements to space-based XCO2 retrievals from the Greenhouse Gases Observing Satellite (GOSAT). Side-by-side measurements of EM27/SUN with the Total Carbon Column Observing Network (TCCON) instrument at the University of Wollongong were conducted in 2015–2016 to derive an XCO2 scaling factor of 0.9954 relative to TCCON. Although we found a slight drift of 0.13 % over 3 months in the calibration curve of the EM27/SUN vs. TCCON XCO2, the alignment of the EM27/SUN proved stable enough for a 2-week campaign, keeping the retrieved Xair values, another measure of stability, to within 0.5 % and the modulation efficiency to within 2 %. From the measurements in Alice Springs, we confirm a small bias of around 2 ppm in the GOSAT M-gain to H-gain XCO2 retrievals, as reported by the NIES GOSAT validation team. Based on the reported random errors from GOSAT, we estimate the required duration of a future campaign in order to better understand the estimated bias between the EM27/SUN and GOSAT. The dataset from the Alice Springs measurements is accessible at https://doi.org/10.4225/48/5b21f16ce69bc (Velazco et al., 2018).

Alkaloid diversity in the leaves of Australian Flindersia (Rutaceae) species driven by adaptation to aridity

The genus Flindersia (Rutaceae) comprises 17 species of mostly Australian endemic trees. Although most species are restricted to rainforests, four have evolved to grow in semi-arid and arid environments. In this study, the leaf alkaloid diversity of rainforest and semi-arid/arid zone adapted Australian Flindersia were compared by LC/MS-MS and NMR spectroscopy. Contrary to expectations, Flindersia alkaloid diversity was strongly correlated with environmental aridity, where species predominating in drier regions produced more alkaloids than their wet rainforest congenerics. Rainforest species were also more chemically similar to each other than were the four semi-arid/arid zone species. There was a significant relationship between the presence of alkaloid structural classes and phylogenetic distance, suggesting that alkaloid profiles are influenced by both genetic and environmental factors. The results suggest that the radiation of Flindersia species out of the rainforest and into drier environments has promoted the evolution of unique alkaloid diversity. Plants growing in arid and semi-arid regions of Australia may represent an untapped source of undescribed specialised metabolites.

Variability of soil moisture proxies and hot days across the climate regimes of Australia

AbstractThe frequency of extreme events such as heat waves are expected to increase due to the effect of climate change, particularly in semiarid regions of Australia. Recent studies have indicated a link between soil moisture deficits and heat extremes, focusing on the coupling between the two. This study investigates the relationship between the number of hot days (Tx90) and four soil moisture proxies (Standardized Precipitation Index, Antecedent Precipitation Index, Mount's Soil Dryness Index, and Keetch‐Byram Drought Index), and how the strength of this relationship changes across various climate regimes within Australia. A strong anticorrelation between Tx90 and each moisture index is found, particularly for tropical savannas and temperate regions. However, the magnitude of the increase in Tx90 with decreasing moisture is strongest in semiarid and arid regions. It is also shown that the Tx90‐soil moisture relationship strengthens during the El Niño phases of El Niño–Southern Oscillation in regions which are more sensitive to changes in soil moisture.

Genome-wide data delimits multiple climate-determined species ranges in a widespread Australian fish, the golden perch (Macquaria ambigua)

Species range limits often fluctuate in space and time in response to variation in environmental factors and to gradual niche evolution due to changes in adaptive traits. We used genome-wide data to investigate evolutionary divergence and species range limits in a generalist and highly dispersive fish species that shows an unusually wide distribution across arid and semi-arid regions of Australia. We generated ddRAD data (18,979 filtered SNPs and 1.725million bp of sequences) for samples from 27 localities spanning the native range of golden perch, Macquaria ambigua (Teleostei; Percichthyidae). Our analytical framework uses population genomics to assess connectivity and population structure using model-based and model-free approaches, phylogenetics to clarify evolutionary relationships, and a coalescent-based Bayesian species delimitation method to assess statistical support of inferred species boundaries. Addressing uncertainties regarding range limits and taxonomy is particularly relevant for this iconic Australian species because of the intensive stocking activities undertaken to support its recreational fishery and its predicted range shifts associated with ongoing climate change. Strong population genomic, phylogenetic, and coalescent species delimitation support was obtained for three separately evolving metapopulation lineages, each lineage should be considered a distinct cryptic species of golden perch. Their range limits match the climate-determined boundaries of main river basins, despite the ability of golden perch to cross drainage divides. We also identified cases suggestive of anthropogenic hybridization between lineages due to stocking of this recreationally important fish, as well as a potential hybrid zone with a temporally stable pattern of admixture. Our work informs on the consequences of aridification in the evolution of aquatic organisms, a topic poorly represented in the literature. It also shows that genome-scale data can substantially improve and rectify inferences about taxonomy, hybridization and conservation management previously proposed by detailed genetic studies.

Short and long-term impacts of ultra-low-volume pesticide and biopesticide applications for locust control on non-target arid zone arthropods

While locust control is necessary to avoid the high cost of locust damage to agriculture, land managers are increasingly seeking to minimize the environmental impact of pesticide spray treatments used. The comparative impacts of different locust control treatments on non-target arid zone fauna are rarely studied in the field, leading to uncertainty as to which treatments represent the lowest hazard to the sprayed ecosystems.A phenyl pyrazole pesticide, fipronil, and a fungal biopesticide, Metarhizium acridum (Green Guard®) were applied aerially in either a barrier or blanket ULV treatment at replicated sites which mimicked the techniques employed for locust control operations in Australia. Effects of the two pesticide treatments were compared in the absence of dense locust populations. We measured the abundance and community composition of non-target arid-zone arthropods at control and treatment sites before and after pesticide applications using a large field-based pitfall trapping experiment.Arthropod community composition was not significantly affected over time by either locust control treatment. However, significant short-term times×treatment interactions were found for 6 of 11 most common taxa at family or higher taxonomic level (collembolans, acarians, coleopterans, psocopterans, gryllids, and dipterans).We also compared unsprayed and sprayed areas within fipronil and Metarhizium treatment sites, and found 2 of the 10 most common ant species (Formicidae: Rhytidoponera mayri and Iridomyrmex purpureus) showed significant time×treatment interactions for fipronil but none for Metarhizium, indicating that ants were more severely affected by fipronil within sites than between the three treatments.One year post-treatment, significant time×treatment interactions persisted for only two taxa (dipterans and blattodeans) at Metarhizium treatments, indicating full recovery of most taxa. The suppression of the ant R. mayri in fipronil sprayed areas within treatment sites persisted after one year, while I. purpureus had fully recovered. Relative arthropod abundance and community assemblage changed over time in control and treatment sites, probably reflecting changes in patterns of local rainfall over the study period.Most of the statistically significant treatment effects recorded for different taxa in our study were not long lasting, suggesting that the two locust control methods studied represent a relatively low and transient hazard to most arthropod taxa. The pronounced temporal variation in arthropod abundance across all sites indicated that climate and environmental factors are likely to be stronger drivers of arid zone arthropod abundance and community structure than single aerial applications of low-dose aerial pesticide treatments used to control locusts in arid and semi-arid regions of Australia.

Mulga, a major tropical dry open forest of Australia: recent insights to carbon and water fluxes

Mulga, comprised of a complex of closely related Acacia spp., grades from a low open forest to tall shrublands in tropical and sub-tropical arid and semi-arid regions of Australia and experiences warm-to-hot annual temperatures and a pronounced dry season. This short synthesis of current knowledge briefly outlines the causes of the extreme variability in rainfall characteristic of much of central Australia, and then discusses the patterns and drivers of variability in carbon and water fluxes of a central Australian low open Mulga forest. Variation in phenology and the impact of differences in the amount and timing of precipitation on vegetation function are then discussed. We use field observations, with particular emphasis on eddy covariance data, coupled with modelling and remote sensing products to interpret inter-seasonal and inter-annual patterns in the behaviour of this ecosystem. We show that Mulga can vary between periods of near carbon neutrality to periods of being a significant sink or source for carbon, depending on both the amount and timing of rainfall. Further, we demonstrate that Mulga contributed significantly to the 2011 global land sink anomaly, a result ascribed to the exceptional rainfall of 2010/2011. Finally, we compare and contrast the hydraulic traits of three tree species growing close to the Mulga and show how each species uses different combinations of trait strategies (for example, sapwood density, xylem vessel implosion resistance, phenological guild, access to groundwater and Huber value) to co-exist in this semi-arid environment. Understanding the inter-annual variability in functional behaviour of this important arid-zone biome and mechanisms underlying species co-existence will increase our ability to predict trajectories of carbon and water balances for future changing climates.

Individual and demographic consequences of reduced body condition following repeated exposure to high temperatures

Although the lethal consequences of extreme heat are increasingly reported in the literature, the fitness costs of exposure to sublethal high air temperatures, typically identified in the 30-40 degrees C range, are poorly understood. We examine the effect of high (> or = 35 degrees C) daily maxima on body condition of a semiarid population of White-plumed Honeyeaters, Ptilotula penicillatus, monitored between 1986 and 2012. During this 26-yr period, temperature has risen, on average, by 0.06 degrees C each year at the site, the frequency of days with thermal maxima > or = 35 degrees C has increased and rainfall has declined. Exposure to high temperatures affected body condition of White-plumed Honeyeaters, but only in low-rainfall conditions. There was no effect of a single day of exposure to temperatures > or = 35 degrees C but repeated exposure was associated with reduced body condition: 3.0% reduction in body mass per day of exposure. Rainfall in the previous 30 d ameliorated these effects, with reduced condition evident only in dry conditions. Heat-exposed males with reduced body condition were less likely to be recaptured at the start of the following spring; they presumably died. Heat-exposed females, regardless of body condition, showed lower survival than exposed males, possibly due to their smaller body mass. The higher mortality of females and smaller males exposed to temperatures > or = 35 degrees C may have contributed to the increase in mean body size of this population over 23 years. Annual survival declined across time concomitant with increasing frequency of days > or = 35 degrees C and decreasing rainfall. Our study is one of few to identify a proximate cause of climate change related mortality, and associated long-term demographic consequence. Our results have broad implications for avian communities living in arid and semiarid regions of Australia, and other mid-latitudes regions where daily maximum temperatures already approach physiological limits in regions affected by both decreased precipitation and warming.

Technical Note: Reducing the spin-up time of integrated surface water–groundwater models

Abstract. One of the main challenges in the application of coupled or integrated hydrologic models is specifying a catchment's initial conditions in terms of soil moisture and depth-to-water table (DTWT) distributions. One approach to reducing uncertainty in model initialization is to run the model recursively using either a single year or multiple years of forcing data until the system equilibrates with respect to state and diagnostic variables. However, such "spin-up" approaches often require many years of simulations, making them computationally intensive. In this study, a new hybrid approach was developed to reduce the computational burden of the spin-up procedure by using a combination of model simulations and an empirical DTWT function. The methodology is examined across two distinct catchments located in a temperate region of Denmark and a semi-arid region of Australia. Our results illustrate that the hybrid approach reduced the spin-up period required for an integrated groundwater–surface water–land surface model (ParFlow.CLM) by up to 50%. To generalize results to different climate and catchment conditions, we outline a methodology that is applicable to other coupled or integrated modeling frameworks when initialization from an equilibrium state is required.

基于CMIP5多模式结果评估人类活动对全球典型干旱半干旱区气候变化的影响

Based on all (ALL) forcing and single-forcing runs from CMIP5 (Coupled Model Intercomparison Project Phase 5) simulations, the present paper examines the anthropogenic influence of greenhouse gases (GHG), anthropogenic aerosols (AA), land use (LU) and combined anthropogenic (Ant) effects on climate change in global arid and semiarid regions. Significant warming is a robust feature over the global land as a response to Ant and GHG forcings, and the warming rate from the latter forcing is two to three times that of ALL forcing results over the past 60 years. AA produces remarkable cooling over the global land surface, whereas LU leads to slight cooling in most arid and semiarid areas. GHG-and Ant-driven increases of precipitation are found in most land areas, especially in arid and semiarid regions. AA and LU produce substantial variation of precipitation over various areas, and current uncertainties are relatively great in AA and LU forcing runs. Ensemble Empirical Mode Decomposition (EEMD) is used to analyze temporal scales of annual temperature and precipitation. The results show that interdecadal and multidecadal variations of temperature and precipitation are attributable to combined natural and anthropogenic forcings in most arid and semiarid regions, where AA dominates variations of both temperature and precipitation on multidecadal timescales. Both GHG and LU have positive effects on multidecadal changes of precipitation over arid and semiarid regions globally. However, the latter significantly prevents multidecadal changes of temperature over arid and semiarid regions of Australia.

Water use and root zone water dynamics of drip-irrigated olive (Olea europaea L.) under different soil water regimes

A field experiment was conducted over 2 years in a semiarid region of Australia to determine the root water uptake–soil water regime relationship and water use of drip-irrigated olive (Olea europaea L.) (cv. Corregiolo). A soil water balance approach was used to estimate the olive trees' water use. Olive evapotranspiration during the first (‘on’) year was 620, 685 and 723 mm for rainfed (during pit-hardening period), deficit (during pit-hardening period) and irrigated treatments, respectively. These values were 555, 610 and 673 mm during the second (‘off’) year. Soil water monitoring in three dimensions was used to infer vertical and lateral root distribution and root activity. The soil water depletion pattern indicated that most of the roots were in the top 60 cm soil depth and aligned along the tree rows. This information is important for fertilizer application and for the placement of drip laterals and soil water measurement equipment used for irrigation scheduling. It also underscores the importance of using three-dimensional models to understand root zone hydrology of drip-irrigated trees.

The Australian desert shrub Eremophila longifolia (R. Br.) F. Muell. (Schrophulariaceae), as a potential source of karahanaenone and other terpenoids

Eremophila longifolia (R. Br.) F. Muell. (Schrophulariaceae) is a shrub endemic to the arid and semi-arid regions of Australia. The plant is used in contemporaneous indigenous traditional medicine and has been cited extensively in medical ethnobotanical literature [1]. This work forms part of an ongoing project investigating variation in essential oil yield and composition from this species. Here we report on the discovery of two novel essential oil chemovarieties, one rich in isomenthone (5-methyl-2-propan-2-ylcyclohexan-1-one), and the other yielding large quantities of the monocyclic heptene ketone karahanaenone (2,2,5,-trimethyl-4-cyclohepten-1-one), Yield and composition was investigated for hydrodistilled leaf essential oils of specimens occurring in semi-arid areas in the state of NSW. Essential oil composition was investigated using a combination of GC/GC-MS. The identity of karahanaenone was established by NMR spectroscopy. Isomenthone type specimens produced essential oils (3.12% –5.65% w/w yield) containing 61.1% –86.7% isomenthone. Karahanaenone type specimens produced essential oils (0.46% –1.90% w/w yield) containing 81.0% –82.2% karahanaenone. This relatively rare natural product and its derivatives are of considerable value to the flavour and fragrance industry and several methods of synthesis from a variety of precursors have been developed [2–5]. Given the potential commercial value of these essential oils as a source of naturally occurring karahanaenone and other compounds, we believe further investigation is warranted into the geographic distribution of these varieties, along with assessment of commercial viability as an agricultural crop for oil production in Australia.

Morphological and genetic variation within the widespread species Acacia victoriae (Mimosaceae)

Morphological variation in Acacia victoriae, a species widespread in arid and semi-arid regions of Australia, was analysed by phenetic methods of classification and ordination. Three morphological groups were identified on the basis of phyllode characters and are treated as subspecies. Populations with short, elliptic and tomentose phyllodes are confirmed as A. victoriae subsp. arida Pedley; this form occurs mainly in central Australia. Populations with linear to oblong, non-tomentose phyllodes are referred to subsp. victoriae; this subspecies is the most variable and widely distributed across Australia. Populations with very long, narrow phyllodes, distributed in northern Australia from the Kimberley to Queensland, are described as fasciaria subsp. nov. A small number of non-tomentose specimens with broad elliptic phyllodes from central Australia require further assessment. Thirteen accessions previously sequenced for internal spacer regions and external spacer regions of ribosomal nuclear DNA showed genetic divergence. Six accessions of subsp. fasciaria formed a clade in a parsimony analysis, confirming that the long phyllode form is genetically distinct.