Subtropical Eastern Australia Research Articles

Paspalum lepton - a valuable adjunct to the suite of grasses used in grazing systems in the subtropics or a potential weed

Native and exotic C4 grasses currently used in grazing systems in the subtropics have specific limitations with management, decline in feed quality as they mature and variable adaptation to soils and climates, providing opportunities to identify alternative species to complement or replace them. One option is Paspalum lepton (syn. P. nicorae), a sward- forming, rhizomatous grass native to subtropical South America with recognized forage value. An early maturing form of this species has become naturalized in Northern New South Wales since its introduction in the 1940s. More recent introductions with forage and amenity potential are being established vegetatively and by seed as it becomes available. This paper reviews published work on P. lepton and reports largely unpublished results and observations on its performance in research and development studies in subtropical Eastern Australia. The potential value of and threats posed by P. lepton in relation to its adaptation, productivity, competitiveness and role in limiting ingress of existing weedy species are discussed. APG 54281 and APG 54325 are palatable, productive and persistent lines of this grass that have proven to be adapted to livestock production systems in most of the humid lowland subtropics, and to a specific niche in the subtropical uplands of Southeast Queensland where there is a lack of adapted C4 grasses and C3 grasses are only marginally adapted.

Does high parasite load contribute to limitation of the poleward range of Acropora corals?

The role of species interactions in setting species range limits is rarely empirically explored. Here, we quantify host and parasite densities in subtropical eastern Australia (26.65°–30.20°S) to examine whether parasitism might contribute to range limitation of Acropora corals at their cold-range boundary. 79% of Acropora corals had endolithic barnacles (family Pyrgomatidae), with higher parasite load in larger corals and up to 141 barnacles per coral. Parasite load increased poleward and closer to the mainland and was greater in cooler and high nutrient environments. Parasite burden was higher at sites with fewer Acropora corals, broadly consistent with the hypothesis that parasites can fragment host populations where host densities are low, and the parasite is a better disperser than the host. Whilst the mechanism is unclear, our findings suggest that at the high densities recorded here, coral-barnacles could influence range dynamics of Acropora corals at their poleward range limit.

Taxa-dependent temporal trends in the abundance and size of sea urchins in subtropical eastern Australia.

Subtropical reefs host a dynamic mix of tropical, subtropical, and temperate species that is changing due to shifts in the abundance and distribution of species in response to ocean warming. In these transitional communities, biogeographic affinity is expected to predict changes in species composition, with projected increases of tropical species and declines in cool-affinity temperate species. Understanding population dynamics of species along biogeographic transition zones is critical, especially for habitat engineers such as sea urchins that can facilitate ecosystem shifts through grazing. We investigated the population dynamics of sea urchins on coral-associated subtropical reefs at 7 sites in eastern Australia (28.196° S to 30.95° S) over 9 years (2010-2019), a period impacted by warming and heatwaves. Specifically, we investigated the density and population size structure of taxa with temperate (Centrostephanus rodgersii, Phyllacanthus parvispinus), subtropical (Tripneustes australiae) and tropical (Diadema spp.) affinities. Counter to expectation, biogeographic affinity did not explain shifts in species abundances in this region. Although we expected the abundance of tropical species to increase at their cold range boundaries, tropical Diadema species declined across all sites. The subtropical T. australiae also showed declines, while populations of the temperate C. rodgersii were remarkably stable throughout our study period. Our results show that temporal patterns of sea urchin populations in this region cannot be predicted by bio-geographic affinity alone and contribute critical information about the population dynamics of these important herbivores along this biogeographic transition zone.

Biogeography of vine thickets and open woodland in subtropical eastern Australia: a case study of three camaenid land snail genera

Dry rainforests and open woodlands occur across much of eastern Australia. However, the biogeographic history of these habitats remains poorly known, especially when compared to nearby moist rainforest areas. Land snails are commonly used as model organisms to understand patterns of origins of regional endemism due to their low vagility. Here we present an analysis of patterns of mitochondrial genetic diversity in three camaenid snail lineages with distributions centred on vine-thicket and open woodland habitats of eastern Queensland, specifically Euryladra from open woodlands, Brigaladra from inland semievergreen vine thickets, and Figuladra from coastal vine thickets. Lineages from habitats west of the Great Dividing Range show relatively low genetic divergence between localities, with particularly low structuring in the open woodland taxon Euryladra. Figuladra from vine-thicket habitats closer to the coast shows relatively deeper genetic divergence, with marked divergences between some upland and lowland areas in south-east Queensland, and across the St Lawrence Gap. This structuring suggests that taxa associated with vine thicket habitats have had a more discernible history of isolation than open woodlands. This said, genetic divergence across many vine thickets patches in lowland coastal regions is also shallow, suggesting many apparently disjunct vine thicket habitats and their associated species also have a recent history of connectivity.

A state-space growth model for Eucalyptus pilularis in subtropical Australia, fitted with and without seemingly unrelated regression

ABSTRACT Inventory data from even-aged, monoculture blackbutt (Eucalyptus pilularis) forests in subtropical eastern Australia were used with the algebraic difference approach to construct a state-space model that predicted stand growth with age for each of quadratic mean diameter, basal area and dominant height, given some initial measurement of the stand. Conventional regression analysis was used to fit each part of the model separately and seemingly unrelated regression (SUR) was used to fit them jointly. Although using SUR resulted in slightly more efficient parameter estimators than when the models were fitted separately, there was no evidence that its use provided any appreciably better fit to the data or precision of estimates of future sizes. Other work in forest science that has used SUR is reviewed briefly and appears to have gained little advantage from its use.

Impact of Facility Location on the Financial Performance of Integrated and Distributed LVL Production in Subtropical Eastern Australia

In subtropical eastern Australia, the declining availability of traditional, large hardwood native forest logs has motivated hardwood sawmills to explore potentially utilising small logs in the manufacture of veneer-based engineered wood products (EWPs), such as laminated veneer lumber (LVL). An aspatial mathematical model that maximises net present value (NPV) over a 30-year project life has been applied to estimate the financial performance of LVL manufacture in this region. Of particular interest was how facility location affected financial performance, and whether distributed production of veneer (close to the log resource) and LVL (distant from the log resource) may be more profitable than integrated production under some circumstances. While integrated production of veneer and LVL near the resource maximised NPV, distributed production was found to be more profitable than integrated production in situations where the LVL manufacturing facility had to be located relatively far from the resource. Nevertheless, the level of value-adding and processing scale had a greater impact on financial performance than facility location. The analysis also highlighted that log procurement strategy substantially affected financial performance. Encouragingly for forest growers and wood processors, utilising large volumes of small diameter logs, was important for maximisation of NPV of larger-scale LVL facilities.

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Quantifying effects on tree growth rates of symmetric and asymmetric inter-tree competition in even-aged, monoculture Eucalyptus pilularis forests

Key messageIn even-aged, monoculture eucalypt forest, symmetric inter-tree competition was far more important in determining tree growth rates than asymmetric competition. Tree size principally determined competitive ability at any time.In even-aged, monoculture forests, individual tree growth rates are much affected by the amount of the resources required for growth (particularly light, water and nutrients) that are available to them from the site on which they are growing. In turn, those amounts are much affected by competition for them between neighbouring trees. Competition may be ‘symmetric’, when tree growth rates are directly proportional to tree sizes, or ‘asymmetric’ when growth rates vary disproportionately with tree sizes. Using a large data set from blackbutt (Eucalyptus pilularis Smith) forests of sub-tropical eastern Australia, methods were devised to quantify the effects of symmetric and asymmetric competition; they were determined as the change each causes in individual tree growth rates over growth periods of a few years. It was found that symmetric competition was by far the principal determinant of tree growth rates. Asymmetric competition had much lesser effects, but was sufficient to alter substantially the development with age of the frequency distribution of tree sizes. It is concluded that the size of a tree at any time is the principal determinant of both its metabolic capabilities for growth and its competitive status and, hence, its growth rate.

A synoptic bridge linking sea salt aerosol concentrations in East Antarctic snowfall to Australian rainfall

Previous research has shown that aerosol sea salt concentrations (Southern Ocean wind proxy) preserved in the Law Dome ice core (East Antarctica) correlate significantly with subtropical eastern Australian rainfall. However, physical mechanisms underpinning this connection have not been established. Here we use synoptic typing to show that an atmospheric bridge links East Antarctica to subtropical eastern Australia. Increased ice core sea salt concentrations and wetter conditions in eastern Australia are associated with a regional, asymmetric contraction of the mid-latitude westerlies. Decreased ice core sea salt concentrations and drier eastern Australia conditions are associated with an equatorward shift in the mid-latitude westerlies, suggesting greater broad-scale control of eastern Australia climate by southern hemisphere variability than previously assumed. This relationship explains double the rainfall variance compared to El Niño-Southern Oscillation during late spring-summer, highlighting the importance of the Law Dome ice core record as a 2000-year proxy of eastern Australia rainfall variability.

The AusPollen partnership project: Allergenic airborne grass pollen seasonality and magnitude across temperate and subtropical eastern Australia, 2016–2020

BackgroundAllergic rhinitis affects half a billion people globally, including a fifth of the Australian population. As the foremost outdoor allergen source, ambient grass pollen exposure is likely to be altered by climate change. The AusPollen Partnership aimed to standardize pollen monitoring and examine broad-scale biogeographical and meteorological factors influencing interannual variation in seasonality of grass pollen aerobiology in Australia. MethodsDaily airborne grass and other pollen concentrations in four eastern Australian cities separated by over 1700 km, were simultaneously monitored using Hirst-style samplers following the Australian Interim Pollen and Spore Monitoring Standard and Protocols over four seasons from 2016 to 2020. The grass seasonal pollen integral was determined. Gridded rainfall, temperature, and satellite-derived grassland sources up to 100 km from the monitoring site were analysed. ResultsThe complexity of grass pollen seasons was related to latitude with multiple major summer-autumn peaks in Brisbane, major spring and minor summer peaks in Sydney and Canberra, and single major spring peaks occurring in Melbourne. The subtropical site of Brisbane showed a higher proportion of grass out of total pollen than more temperate sites. The magnitude of the grass seasonal pollen integral was correlated with pasture greenness, rainfall and number of days over 30 °C, preceding and within the season, up to 100 km radii from monitoring sites. ConclusionsInterannual fluctuations in Australian grass pollen season magnitude are strongly influenced by regional biogeography and both pre- and in-season weather. This first continental scale, Southern Hemisphere standardized aerobiology dataset forms the basis to track shifts in pollen seasonality, biodiversity and impacts on allergic respiratory diseases.

Models Relating Individual Tree Basal Area Growth Rates to Tree Basal Areas in Even-Aged, Monoculture Forest Stands

As trees grow larger in even-aged, monoculture forests, stand density increases, taller trees shade smaller trees and a group of smaller, suppressed trees develops that may show little or no growth. Subsequent mortality is most common from this group. This work compares three models that may describe well the relationship between individual tree basal area growth rates and tree basal areas in a forest stand when a suppressed group of trees is present or not. The models are tested using a large collection of data from permanent sample plots in blackbutt (Eucalyptus pilularis Smith) forests in subtropical eastern Australia. An example is given for one stand showing how model parameter values may change as the stand ages; this illustrates how these models have potential for use in the first stage of model development to relate individual tree growth rates to tree sizes and stand characteristics. Such models may then be used widely across the forest population under consideration.

Citizen Scientists Record Significant Range Extensions for Tropical Sea Slug Species in Subtropical Eastern Australia

The Sea Slug Census program in Australia engages with citizen scientists to record the diversity and distribution of sea slugs across multiple locations. The program has consistently recorded shifts in distribution patterns but a recent, nine-day census in subtropical eastern Australia recorded unprecedented range extensions of tropical species. Seven species (six chromodorids and one polycerid) were found further south of their previously known distribution with Hypselodoris bertschi being recorded for the first time in Australia. These observations suggested the recent transport of larvae via the East Australian Current with recruitment to coastal sites possibly promoted by a protracted period of strong onshore winds associated with the 2021/22 La Niña in the western Pacific. With the increasing frequency of poleward range extensions of marine taxa, citizen science programs such as the Sea Slug Census provide the opportunity to substantially increase monitoring efforts. Linking with iNaturalist strengthens the value of the observations through online peer review to confirm species identities as well as the incorporation of substantiated (Research Grade) records into international biodiversity databases such as GBIF.

Manganese Accumulation and Tissue-level Distribution in the Australian Hyperaccumulator Gossia Bidwillii (Myrtaceae)

The manganese (Mn) hyperaccumulator Gossia bidwillii is a tree species native to subtropical eastern Australia where it occurs on Mn-rich soils. Here, we conducted the first Mn accumulation and tissue-level distribution study on wild and experimentally grown G. bidwillii. Gossia bidwillii plants were subjected to different levels of Mn (250 µg g−1, 500 µg g−1, 1000 µg g−1) soil dosing treatments, whereas the wild G. bidwillii was sampled from growing on highly Mn-enriched natural soils. We used laboratory-based micro-X-ray Fluorescence (µXRF) elemental mapping to elucidate in situ distribution patterns of Mn and other elements in hydrated wild and Mn-dosed G. bidwillii leaves. The data from wild G. bidwillii revealed that it can be strongly Mn-hyperaccumulating with foliar Mn concentrations of 39 000 µg g−1 and 24 000 µg g−1 in old and young leaves, respectively. In the Mn dosing trial, G. bidwillii accumulated 24 400 µg g−1 in old leaves and 17 100 µg g−1 in young leaves in the highest treatment level. The laboratory based µXRF data revealed that Mn is uniformly enriched throughout the laminae and petioles of both young and old leaves in wild G. bidwillii; while in Mn-dosed G. bidwillii, the foliar Mn distribution was primarily concentrated at the leaf-tip and lamina. The approach employed by combining data from the field and controlled experiments was especially meaningful for investigating Mn accumulation in this species and gaining added insight into the phenomenon of Mn hyperaccumulation.

Modelling Maximum Stem Basal Area Growth Rates of Individual Trees ofEucalyptus pilularisSmith

AbstractThe growth rate of a tree at any time relates to its size and the level of competition exerted by its neighbors for the resources it needs for growth. This work describes the development of a model to predict the maximum growth rate in stem basal area of Eucalyptus pilularis Smith trees in native and plantation forests of subtropical eastern Australia. It shows maximum growth rates increasing with size until the tree reaches a stem diameter at breast height of 27 cm. Thereafter, maximum growth rates decline progressively as the tree grows larger. Physiological reasons that might describe this growth pattern are discussed. The maxima are shown to be independent of tree age, stand stocking density or average tree size, and the productive capacity of the site on which the forest is growing.

Modeling cycles and interdependence in irregularly sampled geophysical time series

AbstractWe show how an autoregressive Gaussian process model incorporating a time scale coefficient can be used to represent irregularly sampled geophysical time series. Selection of this coefficient, together with the order of autoregression, provides flexibility of the model appropriate to the structure of the data. This leads to a valuable improvement in the identification of the periodicities within and dependence between such series, which arise frequently and are often acquired at some cost in time and effort. We carefully explain the modeling procedure and demonstrate its efficacy for identifying periodic behavior in the context of an application to dust flux measurements from lake sediments in a region of subtropical eastern Australia. The model is further applied to the measurements of atmospheric carbon dioxide concentrations and temperature obtained from Antarctic ice cores. The model identifies periods in the glacial‐interglacial cycles of these series that are associated with astronomical forcing, determines that they are causally related, and, by application to current measurements, confirms the prediction of climate warming.

Problems with models assessing influences of tree size and inter-tree competitive processes on individual tree growth: a cautionary tale

In forest growing at any one site, the growth rate of an individual tree is determined principally by its size, which reflects its metabolic capacity, and by competition from neighboring trees. Competitive effects of a tree may be proportional to its size; such competition is termed ‘symmetric’ and generally involves competition below ground for nutrients and water from the soil. Competition may also be ‘asymmetric’, where its effects are disproportionate to the size of the tree; this generally involves competition above ground for sunlight, when larger trees shade smaller, but the reverse cannot occur. This work examines three model systems often seen as exemplars relating individual tree growth rates to tree size and both competitive processes. Data of tree stem basal area growth rates in plots of even-aged, monoculture forest of blackbutt (Eucalyptus pilularis Smith) growing in sub-tropical eastern Australia were used to test these systems. It was found that none could distinguish between size and competitive effects at any time in any one stand and, thus, allow quantification of the contribution of each to explaining tree growth rates. They were prevented from doing so both by collinearity between the terms used to describe each of the effects and technical problems involved in the use of nonlinear least-squares regression to fit the models to any one data set. It is concluded that quite new approaches need to be devised if the effects on tree growth of tree size and competitive processes are to be quantified and modelled successfully.

New ages of the world's largest-ever marsupial: Diprotodon optatum from Pleistocene Australia

The extinction of large-bodied terrestrial ‘megafauna’ during earlier phases of the Quaternary had a significant impact on the transforming structure of ecosystems. However, the causes of such losses remains difficult to determine in part because of a paucity of reliable geochronological information about the taxa involved. This is especially true for continents such as Australia where the majority of extinct species have never been dated using radiometric and/or luminescence methods. Here we add new understanding about the geochronology of the world's largest-ever marsupial, the giant wombat-like Diprotodon optatum, an iconic member of the large herbivore guild of Pleistocene Australia. We present 28 new direct U-series ages (dentine) and 10 luminescence ages (sediments) for D. optatum fossils from three sites in tropical north and subtropical eastern Australia. The luminescence ages lie close to saturation for the tropical northern site of Floraville and therefore indicate minimum ages, and sediments from Gowrie Creek in the Darling Downs were mixed and can only be stated as a likely age range. Nevertheless the results assist in our broader understanding of the timing of persistence of the species. Our results demonstrate that the species roamed the northern tropics at least until the mid-Pleistocene (ca. 420 ka). They likely remained widespread during Marine Isotope Stage 5 (ca. 110 ka) and were abundant on the Darling Downs of eastern Australia. The youngest of the new ages that we report (ca. 60 ka) are from Neds Gully on the Darling Downs, a catchment previously considered by some to contain among the last survivors of the now-extinct megafauna. The new dated record demonstrates that deposits of varying ages occur within the catchment. Consequently, existing species lists that treat Neds Gully as a single faunal assemblage are likely significantly time-averaged and overinflated in terms of palaeo-diversity.

The 2019 Southern Hemisphere Stratospheric Polar Vortex Weakening and Its Impacts

AbstractThis study offers an overview of the low-frequency (i.e., monthly to seasonal) evolution, dynamics, predictability, and surface impacts of a rare Southern Hemisphere (SH) stratospheric warming that occurred in austral spring 2019. Between late August and mid-September 2019, the stratospheric circumpolar westerly jet weakened rapidly, and Antarctic stratospheric temperatures rose dramatically. The deceleration of the vortex at 10 hPa was as drastic as that of the first-ever-observed major sudden stratospheric warming in the SH during 2002, while the mean Antarctic warming over the course of spring 2019 broke the previous record of 2002 by ∼50% in the midstratosphere. This event was preceded by a poleward shift of the SH polar night jet in the uppermost stratosphere in early winter, which was then followed by record-strong planetary wave-1 activity propagating upward from the troposphere in August that acted to dramatically weaken the polar vortex throughout the depth of the stratosphere. The weakened vortex winds and elevated temperatures moved downward to the surface from mid-October to December, promoting a record strong swing of the southern annular mode (SAM) to its negative phase. This record-negative SAM appeared to be a primary driver of the extreme hot and dry conditions over subtropical eastern Australia that accompanied the severe wildfires that occurred in late spring 2019. State-of-the-art dynamical seasonal forecast systems skillfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative SAM from as early as late July.

A mathematical model to support investment in veneer and LVL manufacturing in subtropical eastern Australia

In subtropical eastern Australia, hardwood sawmills are exploring opportunities to adapt to declining availability of traditional, large hardwood native forest logs through the manufacture of veneer and laminated veneer lumber (LVL) from comparatively abundant small, native forest logs. This paper introduces an operations research model that evaluates the financial performance of veneer and LVL investment opportunities. Application of the model to subtropical eastern Australia revealed that production and sale of green and dry veneer was not financially viable. One-stage LVL manufacture was profitable at larger scales of production; however, the superior investment alternative was the manufacture of two-stage LVL. Strong economies of scale were revealed in the production of LVL. The mix of logs procured for veneering had a large impact on financial performance due to the combined effects of mill-delivered log cost, the rate at which logs can be processed and veneer recovery from log volume. Encouragingly for forest growers and wood processors, it was optimal for 42.6% of log volume to be small logs at the 30,000 m3 y−1 of log processing scale. The major policy implication arising from this study is that opportunities for processors to profitably manufacture LVL will be enhanced by government forest policy and codes of practice for private land that permit utilisation of small logs, particularly from suppressed trees that will never attain the specifications of traditional log types. The model framework and several parameter estimates adopted for analysis are likely to be useful for forestry decision-making environments outside Australia.

The 2019 flash droughts in subtropical eastern Australia and their association with large-scale climate drivers

During 2017–2019, drought existed in many parts of Australia with varying degrees of severity and varied timing of development and intensification. In a broad sense, the surface climate conditions went from anomalously wet in 2016 to an official government-declared drought from the end of 2017. The drought subsequently intensified further to become most severe in mid to late 2019. Here we explore the more detailed evolution of the 2019 conditions over subtropical eastern Australia and infer its predictability through linear relationships with large-scale climate drivers. To monitor the detailed drought evolution, we use the Evaporative Stress Index (ESI) computed over a 4-week running window on a 5 km grid. Flash drought onset is defined as when there is a rapid decline in the ESI that is sustained over at least 2 weeks which ends in drought conditions. For the Central Slopes area of the upper Darling River basin, flash drought onset occurred in June, persisted over 6 months, and rapidly terminated through a flash recovery in February 2020. In the far east of Australia (East Coast regions), flash drought onset was identified later, in November and December. For the Central Slopes area, less than half the magnitude of the flash drought development in June could be explained through linear relationships with the positive Indian Ocean Dipole mode (IOD) and the central Pacific El Niño, together with the long-term trend in ESI in the region. Similarly, only about half the magnitude of the East Coast flash drought developments in November and December could be explained by the ongoing positive IOD, central Pacific El Niño, negative Southern Annular Mode, and ongoing global warming trend. Therefore, although these large-scale drivers set the stage for the likelihood of drought, successful prediction of flash drought will require more local and current information than those large-scale climate drivers alone.