Geographically-constrained species typically occupy small climatic niches in their native range, and are therefore often assumed to pose a low risk of becoming invasive. However, the association between range size and climatic niche is correlative, and the cause of the constraint, whether it is physiological limits, competition, or dispersal limitations, impacts their risk of becoming invasive. We investigated the interplay between geographic range and niche breadth for the South American tree species Tipuana tipu (Fabaceae), and quantified how the spatial projection of the realised niche may be impacted by this relationship. We constructed a global dataset of location records, including datasets of both non-native and cultivated plants. We constructed a correlative species distribution model (CLIMEX Match Climates), and used ExDet and Ecospat to investigate and characterise niche shift. We found that T. tipu had a large climatic niche, despite having a small geographic native range. Projecting the correlative model indicated a large proportion of Australia and the globe were climatically suitable for T. tipu. Moderate niche shift occurred in all introduced regions, with a significantly greater niche shift amongst datasets of cultivated plants. Geographically-constrained species may have large climatic niches, thereby posing an unanticipated invasion risk in their non-native range. Correlative modelling is a useful tool for modelling species distribution; however, a small geographic range does not guarantee a small climatic niche. Niche shifting may also affect correlative modelling results and their interpretation.

The southern African shrub boneseed [Chrysanthemoides monilifera subsp. monilifera (L.) Norl.] is a perennial shrub that is a significant threat to natural ecosystems and is listed as a Weed of National Significance in Australia. In Western Australia (WA) it has spread across peri-urban and natural environments. We assembled a single standardized database containing more than 2,050 presence records for individual plants and 135 absence records at a local population level. We further refined the populations into 89 sites that require different management trajectories due to topography and capacity of land managers to implement control. Forty-nine of these sites were in urban regions and 40 sites were in regional WA. We split these 89 sites into three near-term management goals: watch (12), extirpate (68), and contain (9). The 12 watch sites are those where all available evidence suggests that there have been no new inputs into the seedbank for 15 yr. The 68 sites marked for extirpation are those where delimitation is already achieved or easily achievable, where there have been minimal seed inputs into the soil seedbank in recent years due to consistent surveillance and control, and where surveys for new plants are likely to be efficient to conduct. Finally, for nine sites in urban regions around Perth, we recommend containment in the near term with a longer-term goal to achieve delimitation and extirpation. To achieve the objective of state-level eradication, a coordinated and sustained campaign involving three components-delimitation of all sites, prevention of further inputs into the soil seedbank, and systematic field surveys to remove plants-must commence without delay. While resourcing requirements for delimitation and overall program management are not possible to estimate, our prior experience suggests that it will take at least 1,900 h of on-ground surveying by experienced personnel to achieve extirpation of C. monilifera subsp. monilifera in WA.

Context Germination is a vulnerable life stage for plants, therefore understanding the dynamics of seed ecology is essential to guiding management recommendations for highly invasive weeds. Aim We addressed the knowledge gap for how seeds contribute to the invasion process for European blackberry (Rubus anglocandicans), a threatening weed across the riparian ecosystems of south-western Australia. Methods We performed mechanical, chemical and thermal treatments on seeds to test for changes in germination success and conducted seed-burial trials to monitor seed viability over time in the soil seedbank. Key results In germination trials, freshly picked and frugivore egested seeds failed to germinate with the endocarp intact. With the endocarp removed, germination remained lower at 4–6 months compared with 10–28 months after collection, indicating a significant after-ripening period. Seeds in intact endocarps survived water immersion for more than 2 months, indicating an ability to survive winter flooding. Acid immersion did not improve germination. The germination success of seeds with endocarp removed increased linearly above 11°C, was greatest at 30°C and thereafter declined rapidly (no survival at 40°C). In a 5-year seed-burial trial, germination varied from 7.6 to 48.4% and was significantly lower closer to a river, and in areas where ‘blackberry decline’ syndrome was present. Conclusions While germination of seed without its pyrene coat occurred over a range of controlled conditions, the natural processes needed to break the pyrene remain unknown. Implications High germination success and the long-term survival of seeds in soil clarifies that the management of blackberry remains a difficult challenge in Australia.

Understanding the historical context of biological invasions can improve weed management outcomes. In this study, we aim to identify the introduction pathway of bitou bush ( Chrysanthemoides monilifera subsp. rotundata ) into Australia and its biogeographical origin in southern Africa by combining multiple lines of evidence from genomic tools and historical documentation. Geographic structure of genomic diversity based on SNPs supported the previous analysis of the invasion pathway of bitou bush between the two countries and within Australia, namely that all Australian material originated from the southern part of the South African distribution. Our synthesis of historical records points to the introduction of this plant into eastern Australia in Newcastle, New South Wales, from its native range in South Africa, via dry shipping ballast in about 1900. Variation in the chloroplast genome was also informative as to the biogeographical origin of Australian material and the context of the introduction. Ten unique haplotypes were discovered in South Africa with only one occurring throughout Australia, indicating an introduction from a single source population to eastern Australia. The matching haplotype was from East London, a port in South Africa with documented shipping connections to Newcastle in eastern Australia, where the weed was first recorded. Historical records suggest that the most plausible explanation for the origins of the isolated bitou bush population in Western Australia is via the shipping of steel billets or landscape plantings associated with shipping companies. The most likely introduction pathway linked the eastern Australian steel processing ports of Newcastle or Port Kembla to the Western Australian port of Kwinana in 1995. Discovering the origin and pathway of bitou bush invasions in Australia opens new opportunities for sourcing biological control agents with a higher chance of impact as well as identifying additional quarantine measures to improve outcomes and reduce long-term costs to management.

Context Despite being a crucial factor in plant growth and fitness, the nutritional requirements of non-native invasive plants are poorly understood and rarely considered when assessing invasion risk; yet, they are particularly relevant in many parts of the world with nutrient-poor soils. Aims We investigated the growth response of a native South American tree species (Tipuana tipu), to soil concentrations of phosphorus (P). T. tipu is widely introduced in some regions of western Australia and South Africa, and we aimed to determine whether soil P availability constrains establishment, naturalisation or invasion of the species. Methods We grew T. tipu (Benth.) Kuntze (Fabaceae), a species that is invasive in some regions, from seed in a glasshouse. All treatments were supplied baseline nutrients, and P from 0 to 640 μg P g−1 dry substrate. Plant height and the number of mature leaves were recorded regularly. Plant biomass, P, and nitrogen (N) concentrations were analysed following destructive harvest. Key results Phosphorus availability had a significant effect on all measured aspects of plant growth. Seed P resources were sufficient to support growth for about 7 weeks, with plants at very low soil P availability (≤5 μg P g−1 dry soil) unable to sustain growth beyond that time. P-toxicity symptoms were observed when substrate P exceeded optimum concentrations (40–160 μg P g−1 dry soil). Conclusions Growth of young T. tipu seedlings was very slow at very low soil P concentrations. Under these conditions, seeds may germinate, and seedlings may survive for a short time, but self-sustaining populations are unlikely to be established. Our study adds to a growing body of research that shows that nutrient requirements of introduced plants and soil nutrient availability influence invasion risk and should be considered in risk assessments for managing species invasions at the landscape level.

There is ample anecdotal evidence and expert opinion on the adverse impact of imported biological control agents on populations of invasive plants, but still a paucity of quantitative data. Asparagus asparagoides (bridal creeper), a perennial climber with an extensive below-ground network of rhizomes and tubers, was considered one of the most invasive plants of natural ecosystems in southern Australia in the 1990s. A long-term experiment was conducted at 15 sites invaded by A. asparagoides across Australia to determine whether its growth and reproduction declined following the release of two biological control agents: a leafhopper (undescribed Erythroneurini formerly referred to as Zygina sp.) and rust fungus (Puccinia myrsiphylli). Data on A. asparagoides were collected annually at each site for up to 3 years before the release of one or both agents in 2000 or 2001, and up to 7 years after release to capture spatial and temporal variability. Our results showed a steady decrease in A. asparagoides seedling and shoot density, and total above-ground biomass in quadrats across all sites in the years following the release of the leafhopper and/or rust fungus. The number of fruits produced in quadrats

Many plants exchanged in the global redistribution of species in the last 200 years, particularly between South Africa and Australia, have become threatening invasive species in their introduced range. Refining our understanding of the genetic diversity and population structure of native and alien populations, introduction pathways, propagule pressure, naturalization, and initial spread, can transform the effectiveness of management and prevention of further introductions. We used 20,221 single nucleotide polymorphisms to reconstruct the invasion of a coastal shrub, Chrysanthemoides monilifera ssp. rotundata (bitou bush) from South Africa, into eastern Australia (EAU), and Western Australia (WAU). We determined genetic diversity and population structure across the native and introduced ranges and compared hypothesized invasion scenarios using Bayesian modeling. We detected considerable genetic structure in the native range, as well as differentiation between populations in the native and introduced range. Phylogenetic analysis showed the introduced samples to be most closely related to the southern-most native populations, although Bayesian analysis inferred introduction from a ghost population. We detected strong genetic bottlenecks during the founding of both the EAU and WAU populations. It is likely that the WAU population was introduced from EAU, possibly involving an unsampled ghost population. The number of private alleles and polymorphic SNPs successively decreased from South Africa to EAU to WAU, although heterozygosity remained high. That bitou bush remains an invasion threat in EAU, despite reduced genetic diversity, provides a cautionary biosecurity message regarding the risk of introduction of potentially invasive species via shipping routes.

Riparian corridors are thought to form hydrological refugia that may buffer species and communities against regional climate changes. In regions facing a warming and drying climate, however, the hydrological regime driving riparian communities is also under threat. We examined recruitment in response to streamflow declines for species inhabiting the riparian zone in southwest Western Australia, testing the extent to which the riparian system has buffered riparian communities from the drying climate. We stratified 49 vegetation transects across the >600 mm per annum regional rainfall gradient encompassed by the Warren River Catchment. Local hydrological conditions were estimated over two 10-year periods; 1980–1989, and 2001–2010, to quantify changes in the flood regime. Mixed effects models tested the relationship between rainfall and flooding on the relative frequency of immature to mature individuals of 17 species of trees and shrubs common to the riparian zones. At the low-rainfall extent of their geographic range, the relative frequency of immature riparian species decreased with declining flow, whereas at the high-rainfall extent of their geographic range the relative frequency of immature individuals increased with declining flow. These results suggest that the geographic ranges of riparian species may be contracting at the low-rainfall margin of their range, while at the high-rainfall margin of their geographic range, reduced flooding regimes appear to be opening up new habitat suitable for recruitment and narrowing the river corridor. No such patterns were observed in upland species, suggesting the river may be buffering upland species. We discuss these findings and their implications for ongoing management and species conservation in a region projected to face further, significant rainfall declines.

Bitou bush (Chrysanthemoides monilifera subsp. rotundata) is a Weed of National Significance in Australia and has impacted a significant portion of the eastern coastline. Its discovery in Western Australia was, therefore, a cause for concern. Assessment and control of the isolated and well-defined population began in 2012. To assess the feasibility of eradication in Western Australia as a management outcome for bitou bush, we applied a rigorous data-driven quantification and prediction process to the control program. Between 2012 and 2018 we surveyed over 253 ha of land and removed 1766 bitou bush plants. Approximately 97 person-days were spent over the six years of survey. We measured the seed bank viability for five years starting in 2013, with the 2017 survey results indicating a decline of mean viable seeds/m2 from 39.3 ± 11.4 to 5.7 ± 2.2. In 2018 we found only ten plants and no newly recruited seedlings in the population. No spread to other areas has been recorded. Soil core studies indicate that the soil seed bank is unlikely to persist beyond eight years. Eradication of the population in Western Australia, defined as five years without plants being detected, therefore remains a realistic management goal. The information generated from the documentation of this eradication program provides invaluable insight for weed eradication attempts more generally: novel detection methods can be effective in making surveys more efficient, all survey methods are not entirely accurate and large plants can escape detection, bitou bush seeds persist in the soil but become effectively undetectable at low densities, and migration of seed was unquantifiable, possibly compromising delimitation. Continued monitoring of the Western Australian population will determine how much of a risk these factors represent to eradication as the outcome of this management program.

Molecular nitrogen (N2) constitutes the majority of Earth's modern atmosphere, contributing ~0.79 bar of partial pressure (pN2). However, fluctuations in pN2 may have occurred on 107–109 year timescales in Earth's past, perhaps altering the isotopic composition of atmospheric nitrogen. Here, we explore an archive that may record the isotopic composition of atmospheric N2 in deep time: the foliage of cycads. Cycads are ancient gymnosperms that host symbiotic N2‐fixing cyanobacteria in modified root structures known as coralloid roots. All extant species of cycads are known to host symbionts, suggesting that this N2‐fixing capacity is perhaps ancestral, reaching back to the early history of cycads in the late Paleozoic. Therefore, if the process of microbial N2 fixation records the δ15N value of atmospheric N2 in cycad foliage, the fossil record of cycads may provide an archive of atmospheric δ15N values. To explore this potential proxy, we conducted a survey of wild cycads growing in a range of modern environments to determine whether cycad foliage reliably records the isotopic composition of atmospheric N2. We find that neither biological nor environmental factors significantly influence the δ15N values of cycad foliage, suggesting that they provide a reasonably robust record of the δ15N of atmospheric N2. Application of this proxy to the record of carbonaceous cycad fossils may not only help to constrain changes in atmospheric nitrogen isotope ratios since the late Paleozoic, but also could shed light on the antiquity of the N2‐fixing symbiosis between cycads and cyanobacteria.

There is an increasing need to understand demographic change to improve management outcomes for controlling invasive alien species. We applied three emerging techniques for recreating past population dynamics-high resolution aerial photography time series, stem growth ring analysis and population level field surveys-to recreate the introduction and invasion history for bitou bush (Chrysanthemoides monilifera subsp. rotundata) in Western Australia. We also compared across dating techniques to test the validity of using stem rings produced by successive cambia for dating purposes, and analysed for the influence of ontogenetic, environmental and morphological factors on stem ring formation. Aerial photography allowed for an accurate recreation of plant presence over time and individual plant age for 18 plants. In a sample of over 500 plants with up to 42 rings, canopy area was related to plant age and ring number, while stem diameter was related to canopy size and ring number. However, stem rings were not produced in a temporally consistent manner and could not be predicted reliably. Up to eight stem rings were produced in younger plants, for which the rate of ring production was greatest. While there was an ontogenetic growth pattern for ring width, no inter-plant synchronisation of ring size was detected, as would be expected if ring size were a response to landscape level climate factors. With aerial imagery and stem ring analysis providing new ways to recreate plant population dynamics at the individual plant level, managers can use this insight to refine conservation and invasion management programs. For bitou bush, such information will focus the duration and location of the current eradication program in Western Australia.

Barrow Island, north-west coast of Australia, is one of the world’s significant conservation areas, harboring marsupials that have become extinct or threatened on mainland Australia as well as a rich diversity of plants and animals, some endemic. Access to construct a Liquefied Natural Gas (LNG) plant, Australia’s largest infrastructure development, on the island was conditional on no non-indigenous species (NIS) becoming established. We developed a comprehensive biosecurity system to protect the island’s biodiversity. From 2009 to 2015 more than 0.5 million passengers and 12.2 million tonnes of freight were transported to the island under the biosecurity system, requiring 1.5 million hrs of inspections. No establishments of NIS were detected. We made four observations that will assist development of biosecurity systems. Firstly, the frequency of detections of organisms corresponded best to a mixture log-normal distribution including the high number of zero inspections and extreme values involving rare incursions. Secondly, comprehensive knowledge of the island’s biota allowed estimation of false positive detections (62% native species). Thirdly, detections at the border did not predict incursions on the island. Fourthly, the workforce detected more than half post-border incursions (59%). Similar approaches can and should be implemented for all areas of significant conservation value.

Sonchus species (Sowthistles) have a world-wide distribution and are serious weeds of crops and the environment. We assessed the suitability of the rust, Miyagia pseudosphaeria, for use in biological control of Sonchus species in Australia and elsewhere. Testing of a limited range of plant species showed the host-range of the rust to be restricted to Sonchus species. We measured spore germination and development of the rust on the host plant in relation to temperature. These measurements, the biology and distribution of the rust, and that of the host S. oleraceus, were used to model the potential world distribution of the rust in CLIMEX. The model indicated that there was limited potential for further spread in Australia; the rust already being widespread. The rust is not present in Canada, but the CLIMEX model indicated that cold temperature will be the main limiting factor for the rust should it be introduced, compromising its suitability as a biological control agent. In South America the rust could potentially be introduced as a biological control agents in areas with Mediterranean and subtropical climate. Molecular studies in combination with more comprehensive inoculation and temperature studies are needed to establish if there are pathotypes of the rust that might be more suitable for use in biological control.

A novel approach for selecting areas to survey for biological control agents, incorporating climate and a hypothesised biological control agent, is demonstrated using the target weed Conyza bonariensis (Asteraceae). This weed has become important in Australian cropping regions due to its persistence and herbicide resistance, and it is also increasingly an environmental weed. Both are reasons for the investigation of biological control options. We developed a species niche model for C. bonariensis in CLIMEX based on parameters informed by plant growth and distribution of the species in the Americas. A hypothetical biological control agent (HBCA-cold) was proposed that has its ideal growth range 5 C below that of the weed, so as to favour development of the agent over that of the weed in parts of Australia. The southern part of the weed's native distribution in Argentina, Chile and the highlands of Ecuador and Columbia were identified as the most suitable areas for surveys that take into account both the climate suitable for the HBCA-cold and the target regions in Australia. This was compared to a model (HBCA-hot) that had an ideal growth range 5 C above that of the weed, but which identified potential areas for surveys in South America that were not climatically aligned with the main regions of the weed's economic impact in Australia. This species distribution modelling method allows for prioritisation of search areas for biological control agents in the case of widespread target species such as C. bonariensis. Crown Copyright (C) 2016 Published by Elsevier Inc. All rights reserved.

In recent years there has been a rapid decline in blackberry (Rubus anglocandicans A.Newton) populations along waterways within the Warren Catchments region located in the south-west of Western Australia. The soil pathogen, Phytophthora bilorbang S.Aghighi, G.E.S.J.Hardy, J.K.Scott & T.I.Burgess, is thought to be instrumental in the decline of these populations. For most waterways in the region, blackberry has dominated the forest understorey for decades. Consequently, the weed’s rapid decline typically results in areas of bare soil or grassed landscapes lacking structure. The blackberry decline created the opportunity to access and restore what were previously often inaccessible but, with the exception of blackberry, fairly pristine landscapes. However, the post-decline absence of blackberry plants within impacted populations is not absolute; scattered individuals persist. Moreover, the decline is not known to impact on what could be a significant blackberry seedbank. Without intervention to restore the landscape, therefore, new blackberry individuals or other weed species could just replace the previous blackberry infestations. Consequently, a follow-up restoration project is underway to increase the resilience of the post-decline community to future weed invasion, including possible blackberry re-invasion. Here we outline the efforts being undertaken to understand these threats and to encourage the successful restoration of these areas within the Warren Catchments region.

Globally, Phytophthora cinnamomi is listed as one of the 100 worst invasive alien species and active management is required to reduce impact and prevent spread in both horticulture and natural ecosystems. Conversely, there are regions thought to be suitable for the pathogen where no disease is observed. We developed a CLIMEX model for the global distribution of P. cinnamomi based on the pathogen's response to temperature and moisture and by incorporating extensive empirical evidence on the presence and absence of the pathogen. The CLIMEX model captured areas of climatic suitability where P. cinnamomi occurs that is congruent with all available records. The model was validated by the collection of soil samples from asymptomatic vegetation in areas projected to be suitable by the model for which there were few records. DNA was extracted, and the presence or absence of P. cinnamomi was determined by high-throughput sequencing (HTS). While not detected using traditional isolation methods, HTS detected P. cinnamomi at higher elevations in eastern Australia and central Tasmania as projected by the CLIMEX model. Further support for the CLIMEX model was obtained using the large data set from south-west Australia where the proportion of positive records in an area is related to the Ecoclimatic Index value for the same area. We provide for the first time a comprehensive global map of the current P. cinnamomi distribution, an improved CLIMEX model of the distribution, and a projection to 2080 of the distribution with predicted climate change. This information provides the basis for more detailed regional-scale modelling and supports risk assessment for governments to plan management of this important soil-borne plant pathogen.