Paul O. Downey

Managing Alien Plants for Biodiversity Outcomes—the Need for Triage

Abstract Recognition that alien plants pose a significant threat to biodiversity has not always translated into effective management strategies, policy reforms, and systems to establish priorities. Thus, many alien plant management decisions for the protection of biodiversity occur with limited knowledge of what needs to be protected (other than biodiversity in a generalized sense) or the urgency of actions. To rectify this, we have developed a triage system that enables alien plant management decisions to be made based on (1) the urgency of control relative to the degree of threat posed to biodiversity, compared with (2) the likelihood of achieving a successful conservation outcome as a result of alien plant control. This triage system is underpinned by a two-step approach, which identifies the biodiversity at risk and assesses sites to determine priorities for control. This triage system was initially developed to manage the threat posed by bitou bush to native species in New South Wales (NSW), Australia. It has subsequently been improved with the national assessment of lantana in Australia, and the adaptation from a single to multiple alien plant species approach on a regional scale. This triage system identifies nine levels of priority for alien plant management aimed at biodiversity conservation, ranging from immediate, targeted action to limited or no action. The development of this approach has enabled long-term management priorities to be set for widespread alien plants that are unlikely to be eradicated. It also enables control to occur in a coordinated manner for biodiversity conservation at a landscape scale, rather than as a series of individual unconnected short-term actions. Nomenclature: Bitou bush, Chrysanthemoides monilifera (L.) Norl.; lantana, Lantana camara L.

Next-Generation Invaders? Hotspots for Naturalised Sleeper Weeds in Australia under Future Climates

Naturalised, but not yet invasive plants, pose a nascent threat to biodiversity. As climate regimes continue to change, it is likely that a new suite of invaders will emerge from the established pool of naturalised plants. Pre-emptive management of locations that may be most suitable for a large number of potentially invasive plants will help to target monitoring, and is vital for effective control. We used species distribution models (SDM) and invasion-hotspot analysis to determine where in Australia suitable habitat may occur for 292 naturalised plants. SDMs were built in MaxEnt using both climate and soil variables for current baseline conditions. Modelled relationships were projected onto two Representative Concentration Pathways for future climates (RCP 4.5 and 8.5), based on seven global climate models, for two time periods (2035, 2065). Model outputs for each of the 292 species were then aggregated into single ‘hotspot’ maps at two scales: continental, and for each of Australia’s 37 ecoregions. Across Australia, areas in the south-east and south-west corners of the continent were identified as potential hotspots for naturalised plants under current and future climates. These regions provided suitable habitat for 288 and 239 species respectively under baseline climates. The areal extent of the continental hotspot was projected to decrease by 8.8% under climates for 2035, and by a further 5.2% by 2065. A similar pattern of hotspot contraction under future climates was seen for the majority of ecoregions examined. However, two ecoregions - Tasmanian temperate forests and Australian Alps montane grasslands - showed increases in the areal extent of hotspots of >45% under climate scenarios for 2065. The alpine ecoregion also had an increase in the number of naturalised plant species with abiotically suitable habitat under future climate scenarios, indicating that this area may be particularly vulnerable to future incursions by naturalised plants.

The grass may not always be greener: projected reductions in climatic suitability for exotic grasses under future climates in Australia.

Climate change presents a new challenge for the management of invasive exotic species that threaten both biodiversity and agricultural productivity. The invasion of exotic perennial grasses throughout the globe is particularly problematic given their impacts on a broad range of native plant communities and livelihoods. As the climate continues to change, pre-emptive long-term management strategies for exotic grasses will become increasingly important. Using species distribution modelling we investigated potential changes to the location of climatically suitable habitat for some exotic perennial grass species currently in Australia, under a range of future climate scenarios for the decade centred around 2050. We focus on eleven species shortlisted or declared as the Weeds of National Significance or Alert List species in Australia, which have also become successful invaders in other parts of the world. Our results indicate that the extent of climatically suitable habitat available for all of the exotic grasses modelled is projected to decrease under climate scenarios for 2050. This reduction is most severe for the three species of Needle Grass (genus Nassella) that currently have infestations in the south-east of the continent. Combined with information on other aspects of establishment risk (e.g. demographic rates, human-use, propagule pressure), predictions of reduced climatic suitability provide justification for re-assessing which weeds are prioritised for intensive management as the climate changes.

Exotic C4 grasses have increased tolerance to glyphosate under elevated carbon dioxide.

The increase in atmospheric CO2 levels can influence the growth of many invasive exotic plant species. However, it is not well-documented, especially for C4 plants, how these growth responses will alter the effectiveness of the worlds most widely used herbicide for weed control, glyphosate. We aimed to address this question by carrying out a series of glasshouse experiments to determine if tolerance to glyphosate is increased in four C4 invasive exotic grasses grown under elevated CO2 in nonlimiting water conditions. In addition, traits including specific leaf area, leaf weight ratio, leaf area ratio, root ∶ shoot ratio, total leaf area, and total biomass were measured in order to assess their contribution to glyphosate response under ambient and elevated CO2 levels. Three of the four mature grass species that were treated with the recommended concentration of glyphosate displayed increased tolerance to glyphosate under elevated CO2. This was due to increased biomass production resulting in a dilution effect on the glyphosate within the plant. From this study, we can conclude that as atmospheric CO2 levels increase, application rates of glyphosate might need to be increased to counteract the growth stimulation of invasive exotic plants. Nomenclature: Glyphosate.

Assessing risk across the spectrum of weed management

A range of risk assessment systems has been applied to the field of weed management globally to address the ever-growing problem of plant invasions. Here, we review the development of risk assessment and management systems across the spectrum of weed management, spanning pre-border (quarantine), post-border (generally aimed at eradication and containment) and the protection of environmental assets. These systems have been developed using broader risk management frameworks, enabling consistency with a range of other agreements and strategies (e.g. pre-border with international phytosanitary measures). While a weed risk assessment system (pre-border) has been developed and widely tested/adopted, post-border systems, especially for established weed species, have been more varied in their nature and application. For example, a triage system has been outlined only recently for managing the current risks of established or widespread weeds to native species. This review also highlights a range of other weed management areas in which risk assessment systems have been applied (e.g. invasion pathways) and where further progress is needed in the current systems to make them more robust. By assessing risk across the spectrum of weed management, we have demonstrated the role of each system and how they link together to address the majority of the spectrum. The application of risk assessment procedures has helped to create systems that aim to prevent, eradicate, contain and protect assets from the effects of weed invasions, the legacy of which will be long lasting, globally.

Managing widespread, alien plant species to ensure biodiversity conservation: a case study using an 11-step planning process.

Abstract One of the greatest threats to biodiversity is the invasion of ecological communities by alien plants. Management strategies for alien plants, however, rarely focus on specific biodiversity-conservation outcomes, and recovery actions rarely address the threat on a landscape scale. There are many reasons for these failures, including (1) limited knowledge of the native species at risk, (2) a disconnect between policy and management, (3) a disconnect between the fields of weed science and biodiversity conservation, (4) a dearth of data from management actions (for both threat abatement and recovery), and (5) the broadly held assumption that control of alien plants will by itself lead to a positive biodiversity response is often incorrect. Thus, alien plant management strategies with a conservation aim need to include planning processes and assessment measures to ensure that the aim is achieved. Here, I outline an example of the planning steps needed to ensure that the management of widespread alien plant species achieves the greatest possible conservation outcome, using the alien plant program for bitou bush (Chrysanthemoides monilifena) as a case study. In addition, I present an overview of the challenges faced and solutions developed during the transition from planning to management, along with some initial data to demonstrate the success and value of this investment in both planning and implementation during the past decade. Interim results from a series of sites have highlighted the success of the program and led to the program being acknowledged as an important ecological restoration project in Australasia. This success is highly dependent on extensive stakeholder involvement (across land tenures), dedicated coordination, and leadership. The planning process is now being adopted for other alien plants in Australia and can be modified to abate the threat from other alien organisms or other threats to biodiversity because the principles of each step are fundamentally similar. Nomenclature: Bitou bush, Chrysanthemoides monilifera (L.) T. Norl. ssp. rotundata (DC.) T. Norl

Functional responses can unify invasion ecology.

We contend that invasion ecology requires a universal, measurable trait of species and their interactions with resources that predicts key elements of invasibility and ecological impact; here, we advocate that functional responses can help achieve this across taxonomic and trophic groups, among habitats and contexts, and can hence help unify disparate research interests in invasion ecology.

A tool to assess potential for alien plant establishment and expansion under climate change

Predicting the influence of climate change on the potential distribution of naturalised alien plant species is an important and challenging task. While prioritisation of management actions for alien plants under current climatic conditions has been widely adopted, very few systems explicitly incorporate the potential of future changes in climate conditions to influence the distribution of alien plant species. Here, we develop an Australia-wide screening tool to assess the potential of naturalised alien plants to establish and spread under both current and future climatic conditions. The screening tool developed uses five spatially explicit criteria to establish the likelihood of alien plant population establishment and expansion under baseline climate conditions and future climates for the decades 2035 and 2065. Alien plants are then given a threat rating according to current and future threat to enable natural resource managers to focus on those species that pose the largest potential threat now and in the future. To demonstrate the screening tool, we present results for a representative sample of approximately 10% (n = 292) of Australias known, naturalised alien plant species. Overall, most alien plant species showed decreases in area of habitat suitability under future conditions compared to current conditions and therefore the threat rating of most alien plant species declined between current and future conditions. Use of the screening tool is intended to assist natural resource managers in assessing the threat of alien plant establishment and spread under current and future conditions and thus prioritise detailed weed risk assessments for those species that pose the greatest threat. The screening tool is associated with a searchable database for all 292 alien plant species across a range of spatial scales, available through an interactive web-based portal at http://weedfutures.net/.

Cost effectiveness in site selection to protect native plant communities from the weed, bitou bush, in New South Wales, Australia.

Government funding to protect native plant communities is usually limited. For cost effectiveness, priority sites for conservation must therefore be identified and funds allocated to protect these sites according to the quantity of communities conserved per dollar of cost. In 1999, invasion of coastal vegetation in New South Wales (NSW) by bitou bush was listed as a key threatening process under the NSW Threatened Species Conservation Act 1995. In accordance with the Act, a Threat Abatement Plan (TAP) was prepared to reduce the impacts of the weed to threatened biodiversity at priority sites. In the present study, data collected for the TAP were analysed by linear programming to determine the feasibility of achieving cost effectiveness in identifying sites and allocating funds, and to explore the impact of associated economic issues on the quantity of native plant communities that are protected. In addition to the total funds and costs per site, the quantity was influenced by alternative funding policies and different site selection strategies. Allocations that recognise these issues can enhance protection outcomes, and promote the cost effectiveness of weed management.

Fictional responses from Vonesh et al.

Vonesh et al. (2017) in their critique of Dick et al. (2017) erect a straw man with their thought experiment; they look for reasons why comparative functional response (CFR) might fail, when CFR clearly and repeatedly succeeds.