Mallee Eucalypt Research Articles

Promoting Optimal Habitat Availability by Maintaining Fine-Grained Burn Mosaics: A Modelling Study in an Australian Semi-Arid Temperate Woodland

The pyrodiversity–biodiversity (P–B) hypothesis posits that spatiotemporally variable fire regimes increase wildlife habitat diversity, and that the fine-grained mosaics resulting from small patchy fires enhance biodiversity. This logic underpins the patch mosaic burning (PMB) paradigm and reinforces the benefits of Indigenous fire management, which tends to promote pyrodiversity. However, tests of the P–B hypothesis and PMB paradigm are few. One of the most comprehensive field evaluations—a snapshot study of pre-existing fire mosaics in south-east Australian semi-arid mallee eucalypt woodlands—found little support. To explore the longer-term effects of fire mosaic grain size on habitat availability and biodiversity, we combined published data from the mallee study with a simple fire simulation. We simulated 500 years of landscape burning under different fire sizes. In the resulting mosaics, we assessed the proportional mixture and patch configuration of successional habitat states, then summarised habitat availability through time using a composite index based on the published fire history responses of 22 vertebrate taxa from the mallee study. Small fires formed fine-grained mosaics with a stable habitat mixture and with habitat diversity occurring at fine scales. Large fires formed coarse-grained mosaics with the opposite properties. The fine-grained mosaics maintained optimal habitat availability for vertebrate diversity over 500 years, while the fluctuating habitat mixture in the coarse-grained mosaics was unlikely to maintain maximum vertebrate diversity. Broadly, our results support the P–B hypothesis and justify further field-testing and evaluation of PMB programs to manage both pyrodiversity and biodiversity in the mallee and other flammable landscapes.

Selection, characteristics, and frequency of use of shelter sites by the Southern Brown Bandicoot Isoodon obesulus obesulus and the Southern Long-nosed Bandicoot Perameles nasuta in a post-fire landscape

ABSTRACT Dense ground cover and understory can be important as diurnal shelter for terrestrial mammals. Fire can lead to the short-term removal of much of this shelter. Here, we report on the shelter site selection of the Southern Brown Bandicoot Isoodon obesulus obesulus and Long-nosed Bandicoot Perameles nasuta eight months after a wildfire. We analysed the number of shelters, frequency of shelter use, nest size, and shelter site microhabitat. Southern Brown Bandicoots used significantly more shelters than Long-nosed Bandicoots. Both species preferred to use shelters with significantly lower levels of transmitted light than matched control areas. Within the burnt landscape, Southern Brown Bandicoots located their refuges under regrowth eucalypts, whereas Long-nosed Bandicoots showed no preference for any microhabitat. Southern Brown Bandicoots built nests significantly higher above ground than Long-nosed Bandicoots. Nests built in more dense and darker microhabitats were significantly taller than those built in more open habitats. Following fire, the Southern Brown Bandicoot required a more dense groundcover to conceal its taller nests and was able to take advantage of regenerating mallee eucalypts for shelter. Land managers need to be aware that hazard reduction burning in coastal woodland and heath will temporarily deprive Southern Brown Bandicoots of diurnal shelter sites and should, therefore, where practicable, retain patches of unburnt dense undergrowth to ensure a mosaic of different aged habitat and habitat structure.

Eucalyptus cryptica (Myrtaceae): a critically endangered new species

Recognition that the critically endangered mallee Eucalyptus sp. Cattai (Gregson s.n. 28 Aug 1954) is a distinct species has been complicated by close morphological similarity between it and other members of E. subgenus Symphyomyrtus section Latoangulatae series Annulares. Recent genomic evidence has demonstrated that it is distinct from other species. In this study, we provide E. sp. Cattai with the new species name, E. cryptica T.C.Wilson, S.Rutherf. & S.M.Douglas, and use genomic scans of adults and seedlings to assist in its description and support its conservation by identifying hybrids. Accompanying the description of E. cryptica are images, diagnostic illustrations and an updated part of the Eucalyptus key for the Flora of New South Wales.

First record of the Mallee Whipbird Psophodes nigrogularis leucogaster in Victoria since 1985

The Mallee Whipbird (White-bellied Whipbird) Psophodes nigrogularis leucogaster is a threatened passerine restricted to mallee-heath vegetation in the Eyre Peninsula, Yorke Peninsula and southern Murray Mallee region of eastern South Australia and western Victoria. This taxon is both difficult to detect and has undergone significant declines in range and abundance over the past century. The last records in Victoria were made in 1985 in the Big Desert State Forest. Here, we report a new record in the Big Desert Wilderness Park made in October 2022. This record was the result of extensive field surveys targeting this and other threatened mallee bird taxa. We also recorded the Mallee Whipbird in the adjoining Ngarkat Conservation Park (South Australia), 5 years after the most recent record in that reserve and only the second record there after extensive wildfires in 2014. Both records were in vegetation burnt 8 years earlier, with a mix of low whipstick mallee (Narrow-leaved Red Mallee Eucalyptus leptophylla) and diverse regenerating heath vegetation. The Mallee Whipbird must now be considered one of Victoria’s rarest resident birds, with only one location known for the state.

Carbon dynamics in tree plantings: How changes in woody biomass impact litter and soil carbon

Understanding carbon sequestration from tree planting and management activities is important for contributing to the mitigation of climate change. Although rates of growth and resulting sequestration of carbon in live above-ground biomass are relatively well understood in various woody plantings and commercial plantations in Australia, less is known about associated changes in live below-ground biomass, and the turnover and decomposition of biomass, and hence, resulting changes in carbon stocks of litter and soil. Our objective was to develop a modelling approach for predicting these processes and the resulting changes in litter and soil carbon following the establishment and/or management of tree plantings (EMTP) to facilitate their inclusion in carbon abatement projects. We reviewed and collated data on allocation of biomass, litterfall, litter decomposition, litter/harvest residue mass and soil organic carbon (N = 5,655 estimates). Data were sourced from existing field studies of woody plantings (mixed-species environmental and mallee eucalypt), commercial plantations (hardwood and softwood) and in some cases, eucalypt-dominant native forests. After constraining a carbon accounting model to observed measures of growth, allocation of biomass, and rates of litterfall and litter decomposition, the model was calibrated to maximise the efficiency of prediction of litter and soil pools. Although large uncertainties in ‘observed’ results meant that precision of prediction in any given data source was relatively poor, model predictions had negligible overall bias. The size and diversity of datasets applied in the process of calibration improved overall confidence in model predictions of litter and soil carbon pools. The calibrated model will therefore be a useful tool for informing land managers and policy makers seeking to understand on-site dynamics of all carbon pools, and hence, the total contribution to carbon abatement of different EMTP projects in Australia.

Testing New Provenances of Eucalyptus polybractea: A Eucalypt Oil Mallee Adapted to Semi-Arid Environments

Novel genetic accessions of Eucalyptus polybractea from a previously untested, hotter and drier part of the species’ natural range were tested in a common garden trial at a semi-arid site in NSW, Australia. Eucalyptus polybractea is a mallee eucalypt cultivated for essential oils (1,8-cineole), bioenergy and carbon sequestration on dryland sites in southern Australia (sites receiving about 450 mm mean annual rainfall, MAR). A trial of six previously untested provenances from the relatively hot, dry part of the species’ natural range in South Australia (SA) (250–450 mm MAR) was established alongside seven provenances from New South Wales (NSW) and Victoria within a commercial plantation in NSW. The trial was assessed at age 3.7 years for growth and oil characteristics. While survival was excellent, most of the SA sources were slower growing and of sub-standard oil concentration and quality relative to those from Victoria and NSW. However, a single SA provenance, with the highest oil concentration and 1,8-cineole percentage of all provenances tested, may have potential as a source of selected germplasm. Infusion of SA material into the breeding populations of E. polybractea, which are currently based on NSW and Victorian selections only, may provide more resilience in the face of hotter and drier temperatures expected under projected climate change scenarios, and/or allow the introduction of the species to hotter and drier climates in Australia or other parts of the world with semi-arid climates. However, high-intensity selection of infusions will be required to maintain the growth and oil characteristics in the existing breeding population.

In the Hot Seat: Behavioral Change and Old-Growth Trees Underpin an Australian Songbird’s Response to Extreme Heat

Anthropogenic climate change is increasing the frequency and intensity of heat waves, thereby threatening biodiversity, particularly in hot, arid regions. Although free-ranging endotherms can use behavioral thermoregulation to contend with heat, it remains unclear to what degree behavior can buffer organisms from unprecedented temperatures. Thermoregulatory behaviors that facilitate dry heat loss during moderate heat become maladaptive once environmental temperatures exceed body temperature. Additionally, the costs associated with behavioral thermoregulation may become untenable with greater heat exposure, and effective cooling may be dependent upon the availability of specific microhabitats. Only by understanding the interplay of these three elements (responses, costs and habitat) can we hope to accurately predict how heat waves will impact wild endotherms. We quantified the thermoregulatory behaviors and microhabitat use of a small passerine, the Jacky Winter (Microeca fascinans), in the mallee woodland of SE Australia. At this location, the annual number of days ≥ 42°C has doubled over the last 25 years. The birds’ broad repertoire of behavioral responses to heat was nuanced and responsive to environmental conditions, but was associated with reduced foraging effort and increased foraging costs, accounting for the loss of body condition that occurs at high temperatures. By measuring microsite surface temperatures, which varied by up to 35°C at air temperatures > 44°C, we found that leaf-litter coverage and tree size were positively correlated with thermal buffering. Large mallee eucalypts were critical to the birds’ response to very high temperatures, providing high perches that facilitated convective cooling, the coolest tree-base temperatures and the greatest prevalence of tree-base crevices or hollows that were used as refuges at air temperatures > 38°C. Tree-base hollows, found only in large mallees, were cooler than all other microsites, averaging 2°C cooler than air temperature. Despite the plasticity of the birds’ response to heat, 29% of our habituated study population died when air temperatures reached a record-breaking 49°C, demonstrating the limits of behavioral thermoregulation and the potential vulnerability of organisms to climate change.

Genomic data inform conservation of rare tree species: clonality, diversity and hybridity in Eucalyptus series in a global biodiversity hotspot

Rare species are key targets of biodiversity conservation worldwide, but assessments of genetic diversity and conservation priority can be impeded by limited sample size. Reduced-representation genome sequencing improves resolution of analysis in this context, enabling applications in conservation genomics. The tree genus Eucalyptus contains many rare taxa, but clarity on conservation actions can be confounded in this group due to taxonomic complexity, unrecognised clonality and hybridisation. Using SNPs, we address key questions surrounding taxonomy, clonality and genetic diversity in two rare species, Eucalyptus virginea and a putative hybrid E. × phylacis, to inform conservation. We confirm that a highly disjunct population belongs to E. virginea despite sharing a multi-stemmed short-statured (‘mallee’) growth form and geographic proximity with a closely-related species, indicating that growth form was unrelated to phylogenetic distance. Clonality was confirmed in the disjunct population but the number of discrete clumps vs unique genets was not equal, reflecting the importance of genetic assessments of population size. The small, clonal, disjunct population had the lowest allelic richness and highest differentiation, as expected. However, heterozygosity excess suggested that clonality may prevent the loss of heterozygosity in mallee eucalypts by facilitating long-term persistence, contrary to expectations that small, isolated populations face increased conservation genetic threat. Analyses also confirmed that the Critically Endangered E. × phylacis is an F1 hybrid of E. decipiens and E. virginea, therefore its conservation listing should be revised. Our data highlight the usefulness of genomic analysis in applied conservation of non-model taxa.

Genetic parameters and potential gains from breeding for biomass and cineole production in three-year-old Eucalyptus polybractea progeny trials

ABSTRACT Eucalyptus polybractea is a mallee eucalypt with potential use as a perennial biomass crop for dryland agriculture in southern Australia, in addition to its established success as a source of eucalyptus oil. Sixty-six indigenous, open-pollinated families from West Wyalong and surrounds in New South Wales were tested in trials at Newdegate, Western Australia; Drummartin, Victoria; and Condobolin, New South Wales. Growth was fastest at Condobolin, followed by Drummartin then Newdegate. The estimated cross-site genetic correlation was rg = 0.85 ± 0.16 between Newdegate and Condobolin, rg = 1.08 ± 0.35 between Newdegate and Drummartin, and rg = 1.03 ± 0.32 between Condobolin and Drummartin. Estimated gains suggest that genotype × environment interaction was not practically significant. Narrow-sense heritability for biomass production was ĥ2 = 0.18 ± 0.07 at Newdegate, ĥ2 = 0.05 ± 0.04 at Drummartin and ĥ2 = 0.32 ± 0.08 at Condobolin. Heritability of leaf cineole concentration at Newdegate was ĥ2 = 0.38 ± 0.09. The genetic correlation between leaf cineole concentration and biomass production was rg = 0.07 ± 0.19 and the phenotypic correlation was rp = −0.12 ± 0.03. Compared to selection on either tree biomass or leaf cineole concentration, index selection incorporating both whole tree biomass and leaf cineole concentration is most effective when looking to maximise both cineole yield and biomass production.

Divergent lineages in a semi-arid mallee species, Eucalyptus behriana, correspond to a major geographic break in southeastern Australia.

AimTo infer relationships between populations of the semi‐arid, mallee eucalypt, Eucalyptus behriana, to build hypotheses regarding evolution of major disjunctions in the species' distribution and to expand understanding of the biogeographical history of southeastern Australia.LocationSoutheastern Australia.Taxon Eucalyptus behriana (Myrtaceae, Angiospermae).MethodsWe developed a large dataset of anonymous genomic loci for 97 samples from 11 populations of E. behriana using double digest restriction site‐associated DNA sequencing (ddRAD‐seq), to determine genetic relationships between the populations. These relationships, along with species distribution models, were used to construct hypotheses regarding environmental processes that have driven fragmentation of the species’ distribution.ResultsGreatest genetic divergence was between populations on either side of the Lower Murray Basin. Populations west of the Basin showed greater genetic divergence between one another than the eastern populations. The most genetically distinct population in the east (Long Forest) was separated from others by the Great Dividing Range. A close relationship was found between the outlying northernmost population (near West Wyalong) and those in the Victorian Goldfields despite a large disjunction between them.ConclusionsPatterns of genetic variation are consistent with a history of vicariant differentiation of disjunct populations. We infer that an early disjunction to develop in the species distribution was that across the Lower Murray Basin, an important biogeographical barrier separating many dry sclerophyll plant taxa in southeastern Australia. Additionally, our results suggest that the western populations fragmented earlier than the eastern ones. Fragmentation, both west and east of the Murray Basin, is likely tied to climatic changes associated with glacial‐interglacial cycles although it remains possible that major geological events including uplift of the Mount Lofty Ranges and basalt flows in the Newer Volcanics Province also played a role.

Determinants of the economic viability of mallee eucalypts as a short rotation coppice crop integrated into farming systems of Western Australia

AbstractMallee eucalypts are being developed as a short rotation coppice crop for integration into agricultural systems in the south‐west of Western Australia. These have potential for biomass production for bioenergy, eucalyptus oil and generating carbon credits and to help control the extensive occurrence of dryland salinity. Some 12,000 ha of mallee planting has been undertaken since 1994, mostly in the form of wide‐spaced, narrow belts within the annual agricultural system. Production and market data were used to estimate levelized costs (LC) of mallee biomass production under different harvest regimes across 11 sites from 2006 to 2012. We found LC ranged from AUD40 to AUD257 fresh Mg−1. LC was most strongly determined by mallee production, followed by the crop/pasture rotation decisions of the landholder. Mallee harvest regime had minor impact on LC. Crop and pasture yield loss due to competition from the mallee belts accounted for 38% of costs, harvesting biomass was 32%, opportunity cost of the land occupied by the mallee belts was 16% while establishment and maintenance costs accounted for 14% of the costs. When income from carbon sequestered in mallee root biomass was included, the LC dropped by an average of 11% at the current Australian price of AUD15 Mg−1 CO2 equivalent (CO2e). The income from carbon sequestered in root biomass alone is unlikely to make mallee agroforestry economically viable. Hence, income from harvested biomass in the form of feedstocks for industry or carbon credits is necessary to make mallee agroforestry commercially attractive. LC for unharvested mallee belts ranged from AUD33 to AUD237 Mg−1. Where above‐ and below‐ground biomass is converted to CO2e at AUD15 Mg−1, the LC drops to AUD11–AUD64, with three of 11 sites likely to be profitable. These three sites were characterized by high biomass production with low agricultural gross margins.

Planting configuration affects productivity, tree form and survival of mallee eucalypt in farm forestry plantings

Mallee eucalypts have been extensively planted in the Western Australia wheatbelt for salinity mitigation and as a short-rotation coppice crop for the production of cineole and bioenergy feedstocks. Mallee has been planted in wide-spaced narrow belts (2–6 rows) within annual crops and pasture, but optimal planting configurations have not been determined. Here, we assess the biomass yield responses of Eucalyptus loxophleba ssp. lissophloia and E. polybractea to; four row treatments (1, 2, 4 and 6 row belts) and five within-row spacing treatments (1, 1.5, 2, 3 and 4 m). Thirteen years after planting, the row effects on plot-level biomass productivity of E. loxophleba ranged from 4.3 to 21.2 Mg ha−1 year−1. For E. polybractea, both row number and within-row spacing affected yield, which ranged from 2.7 to 18.8 Mg ha−1 year−1. For both species, the highest growth rates were observed in the one-row belts with shorter (< 3 m) within-row spacing. Within the belts, reductions of growth rate were observed with additional rows, due to increased competition and significant suppression of internal rows; and with wider within-row spacing, due to lower initial planting density. However, when including the area between belts, wider belts generated more biomass. For both species, average tree size decreased with additional rows and shorter within-row spacing. For both species, the number of stems per tree increased with wider within-row spacing, and also for E. polybractea, with fewer rows. The substantial variation in productivity, tree size and form found in these results will affect harvestability and ultimately the economic viability of future mallee plantings.

A decadal multi-site study of the effects of frequency and season of harvest on biomass production from mallee eucalypts

Mallee eucalypts are hardy, woody perennials that are being developed as a short-rotation coppice crop in Australia for the production of eucalyptus oil, biofuels and other biomass products. The economic viability of this prospective crop is dependent on its ability to survive and regenerate following repeated harvesting of the above ground component. Here we report on survival and biomass yield of mallee belt plantings of Eucalyptus polybractea, E. loxophleba ssp lissophloia and E. kochii ssp plenissima, at 19 sites, under two harvest-frequencies (3–8 year cycles) and harvest seasons (autumn or spring) over a decade from 2006 to 2015. 16 sites had post-harvest mortality ranging from 1.0% to 12.2% while the remaining three sites with either shallow saline water tables or a silcrete hardpan failed. Average site dry biomass yield across treatments ranged from 2.2 to 32.8 Mg ha−1 yr−1. Higher yielding sites were generally characterised by pH between 3.8 and 8, ECe below 15.0 dS m−1 and high soil fertility. Lower yielding sites were generally near saline valley floors. After 7-years, biomass yield from unharvested treatments exceeded the average cumulative yield of harvest treatments at eight of the 16 sites, including all three E. kochii sites. For E. loxophleba, significant interactions were found between season and frequency of harvest with highest yields in long rotation spring treatments. There were also interactions between site and frequency of harvest, which were mainly driven by the variable performance of the uncut treatment. On average E. loxophleba yielded more biomass following spring harvests whereas E. kochii yielded more following autumn harvests. E. polybractea yield was unaffected by season or frequency of harvest; however, harvest treatments yielded more biomass than uncut treatments. After 10 years, at eight of the nine sites subjected to three 3-year cycles, no decline in biomass yield was observed. The site that declined in production was attributed to depletion of a sandplain aquifer by extensive mallee plantings. Overall, the results from this decadal study indicate that in warm-temperate semi-arid areas, such as the south-west of WA, mallees biomass can be harvested sustainably at most sites even in short (3-year) rotation cycles.

Testing the generality of below-ground biomass allometry across plant functional types

Accurate quantification of below-ground biomass (BGB) of woody vegetation is critical to understanding ecosystem function and potential for climate change mitigation from sequestration of biomass carbon. We compiled 2054 measurements of planted and natural individual tree and shrub biomass from across different regions of Australia (arid shrublands to tropical rainforests) to develop allometric models for prediction of BGB. We found that the relationship between BGB and stem diameter was generic, with a simple power-law model having a BGB prediction efficiency of 72–93% for four broad plant functional types: (i) shrubs and Acacia trees, (ii) multi-stemmed mallee eucalypts, (iii) other trees of relatively high wood density, and; (iv) a species of relatively low wood density, Pinus radiata D. Don. There was little improvement in accuracy of model prediction by including variables (e.g. climatic characteristics, stand age or management) in addition to stem diameter alone. We further assessed the generality of the plant functional type models across 11 contrasting stands where data from whole-plot excavation of BGB were available. The efficiency of model prediction of stand-based BGB was 93%, with a mean absolute prediction error of only 6.5%, and with no improvements in validation results when species-specific models were applied. Given the high prediction performance of the generalised models, we suggest that additional costs associated with the development of new species-specific models for estimating BGB are only warranted when gains in accuracy of stand-based predictions are justifiable, such as for a high-biomass stand comprising only one or two dominant species. However, generic models based on plant functional type should not be applied where stands are dominated by species that are unusual in their morphology and unlikely to conform to the generalised plant functional group models.

Biogeochemical expression of buried iron-oxide‑copper‑gold (IOCG) mineral systems in mallee eucalypts on the Yorke Peninsula, southern Olympic Domain; South Australia

We report on the results of a regional scale biogeochemical sampling program conducted on the Yorke Peninsula, South Australia, utilising four locally occurring Eucalyptus species with mallee-form. Our purpose is to determine if there is an empirical relationship between Cu accumulation in the mallee leaves and elevated Cu in the underlying basement rocks – such that the mallee species might be a useful biogeochemical exploration tool in this area. The basement rocks of the Yorke Peninsula are prospective for iron oxide‑copper‑gold (IOCG) mineralisation but are mantled by Cambrian to Quaternary sedimentary rocks of variable thickness that inhibit traditional surface geochemical exploration techniques. There is no evidence to link Cu concentrations to dust contamination or fertiliser usage. Leaves of the four mallee species have comparable log normal population distributions of Cu, with a range between 1.6ppm and 10ppm. Higher concentrations of Cu (>6ppm) occur more commonly within 3km of known Cu occurrences. These results suggest that all four mallee species have the ability to concentrate higher amounts of Cu in their leaves when the underlying/local geology also contains elevated Cu. The results suggest that biogeochemical sampling of multiple mallee species over large regions could be a useful exploration technique in covered areas of southern Australia where mallee species are widespread and densely populated.

Evidence for adaptation and acclimation in a widespread eucalypt of semi-arid Australia

As climates change, restoration programmes need to maximize the capacity of regenerating ecosystems to adapt to new environments, particularly when planting long-lived trees. By using a combined phenotypic and genomic approach, we assessed evidence of adaptation capacity in Eucalyptus loxophleba ssp. lissophloia, a mallee eucalypt important for restoration and oil production in Western Australia. Assessment of leaf traits in nine wild populations across a rainfall gradient showed that two traits were correlated with long-term moisture availability. Populations in more arid environments had lower specific leaf area and lower stomatal conductance, consistent with a stable plastic or adaptive response. Other leaf size and shape traits were correlated with short-term climate variables, suggesting a dynamic plastic response. Genome-wide scans with 4851 DArTseq markers and outlier analysis detected 50 markers showing signals of disruptive selection, consistent with local adaptation. Sixteen markers showed allele frequencies correlated with aridity; three were also associated with differences in stomatal conductance. Multivariate analysis and marker-environment associations signalled secondary directions of adaptation associated with maximum temperatures and soil phosphorus. We suggest that adaptation and acclimation are both likely determinants of functional phenotype in E. loxophleba, and argue that aridity is a critical driver of adaptation in this widespread species.

Life cycle assessment of a mallee eucalypt jet fuel

This study uses life cycle assessment to quantify and compare the greenhouse gas emissions and fossil fuel depletion impacts of a theoretical mallee jet fuel value chain, operating in the Great Southern region of Western Australia, with those of fossil-based jet fuel. Relative to fossil-based jet fuel, the mallee jet fuel was found to reduce greenhouse gas emissions by 40% and result in a net fossil fuel depletion benefit. Further greenhouse gas reductions could be achieved by optimizing the supply chain through measures such as capturing methane emissions for hydrogen production and utilizing co-produced biodiesel. The magnitudes of the environmental benefits are sensitive to a number of methodology assumptions, including the approach to potential food displacement and co-production.

Age‐related susceptibility ofEucalyptusspecies toPhytophthora boodjera

Phytophthora boodjerais a newly described pathogen causing damping off and mortality ofEucalyptusseedlings in Western Australian nurseries. This study evaluated the age‐related susceptibility of several taxa of malleeEucalyptustoP.boodjerain sterilized washed river sand‐infestation pot trials.Phytophthora cinnamomiandP.arenariawere included for comparison. Seedlings ofEucalyptustaxa were inoculated at 0, 2, 4, 12 and 88 weeks with individualPhytophthoraisolates. Pre‐emergent mortality in the presence ofPhytophthorawas almost 100%. Post‐emergent mortality was 50–100%, depending on isolate, compared to 0% for the control. Mortality was also high for inoculated 1 month‐old seedlings (46–68%) and root length of surviving seedlings was severely reduced. Death from root infection was not observed for seedlings inoculated at 12 and 88 weeks, but they developed root necrosis and reduced root dry weight compared to non‐inoculated controls.Phytophthora boodjerais a pre‐ and post‐emergent pathogen of mallee eucalypts. These eucalypts are susceptible toP. boodjeraat all life stages tested, but the mortality rates declined with plant age. Similar results were obtained forP. cinnamomiandP. arenaria. The events leading to its recent appearance in the nurseries remain unknown and further investigations are underway to determine if this is an introduced or endemic pathogen. The approach used here to understand the impact of aPhytophthoraspecies on multiple hosts at different seedling ages is novel and sets a benchmark for future work.

Aviation biofuel from integrated woody biomass in southern Australia

A synthesis of work on integrating short‐rotation biomass plantings into existing mixed crop and livestock farming regimes with the biomass being converted to biofuels, including aviation fuel, is provided. This agroforestry system, based on mallee eucalypt species native to Australia, provides broader environmental benefits, including biodiversity protection. These species are suited to the edaphic and climatic conditions of rainfed farming systems in southern Australia. The study focused on the Great Southern region of Western Australia, with an average annual rainfall of 400–600 mm. Compared to other locations in Australia, significantly more research and development has been conducted in this region, with a mallee biomass‐to‐jet fuel business case and farmer cooperation providing reliable data for assessing the viability and sustainability of commercial supply chain development. The limited capacity of Australian agricultural systems to produce biomass due to the relatively dry climate means that the available biomass resources should be directed to strategically important energy uses such as aviation fuel. Technical, economic, and environmental insights gained from these long‐term studies have demonstrated that it is feasible to integrate this new production system into the overall farming enterprise and indicate strong prospects for a biomass industry in this region should political and economic uncertainties currently facing the renewable energy industry in Australia be resolved. WIREs Energy Environ 2017, 6:e221. doi: 10.1002/wene.221This article is categorized under: Bioenergy &gt; Science and Materials Bioenergy &gt; Economics and Policy Bioenergy &gt; Systems and Infrastructure

Spinifex–mallee revegetation: implications for restoration after mineral-sands mining in the Murray–Darling Basin

Mineral-sands mining in the semiarid and arid zone of south-eastern Australia is now a widespread disturbance that may adversely affect large areas of remnant vegetation, including mallee (Eucalyptus spp.) with hummock grass or spinifex (Triodia scariosa) understorey. No broad-scale restoration projects have been undertaken to revegetate mallee Eucalyptus species with spinifex. We report on the survivorship and relative importance (spatial coverage) of hand-planted tubestock 10 years after establishment in 2001, which included mallee Eucalyptus, Triodia scariosa, Acacia spp. and Hakea spp. These taxa are the dominant plants in a semiarid dune–swale system on a former mineral-sands mine licence area in semiarid, north-western Victoria. Mean survivorship of tubestock was 0.58 ± 0.04. Spinifex (Triodia scariosa), needlewood (Hakea) and several mallee species (Eucalyptus spp.) survived substantially better than the average of all tubestock-planted species, although Acacia spp. had low survivorships. Although the plantings were undertaken in the early stages of the most severe drought in the instrumental record (the ‘Millennium drought’), several taxa survived well and species such as spinifex established and developed ground coverage greater than the benchmark values for the ecological vegetation class of the location. We conclude that hand-planting of tubestock can achieve restoration objectives for this component of spinifex–mallee vegetation, even under extremely arduous conditions associated with long-term drought. We also herald the importance of taking a long-term view to the assessment of revegetation success, in this case 10 years.