The main objective of this work package (WP) is to develop future intervention scenarios of invasive species management together with other scientists and stakeholders through a process of Participatory Scenario Planning (PSP). This is an increasingly used tool that facilitates exploration of the future evolution of complex systems, thereby providing information for decision-making (Palomo et al. 2017). First, we will select a number of Invasive Species of Interest in Europe and the United States that will be the focus of research in the following WPs. In Europe, between 20 and 50 species will be selected to cover various habitats (freshwater, terrestrial, marine), stages of invasion (non-established through to widespread) and impacts (Minimal to Massive, positive and negative). The selection of species will accommodate the research needs of all WPs, which may focus on subsets of the species list, depending on the WP’s objectives, data and resources availability. Priority will be given to species already included or expected to be included in the “List of IAS of EU concern”, a list of 49 (+18 candidates) plants and animals whose management has been prioritised by the European Union under Regulation 1143/2014. In the absence of similar official species listings in the US, we will first collate information about the impacts of invasive species on biodiversity and ecosystem services with EICAT and then select 100 high-risk plants and marine organisms.

Intervention scenarios will use as reference the Alien Species Narratives (ASNs), developed by AlienScenarios (https://alien-scenarios.org/, Essl et al. 2019), another BiodivERsA-Belmont Forum project closely related to InvasiBES. ASNs are qualitative narratives of plausible futures of global invasive species richness (Lenzner et al. 2019) that will serve as a framework to explore the impacts of different levels of policy implementation. For InvasiBES, we envision two extreme possible intervention situations: under a scenario, invasive species are not managed and, by 2050, they are able to fill their potential climate range modelled in WPs 3 and 4, fostered by increasing globalisation. Under a scenario, international co-ordinated actions prevent the arrival of new invaders – through, for instance, border control and trade regulations – and existing invasive species are managed via eradication techniques and ecological restoration. In between, a number of scenarios can be drawn, ideally through a participatory process involving stakeholders with practical experience in environmental management and ecosystem restoration. In all cases, intervention scenarios will consider all stages of the invasion process and the cost-effectiveness, practicality and acceptability of alternative management options (following Booy et al. 2017).

The main objective of this WP is to adapt and validate impact assessment protocols considering both the detrimental and beneficial impacts of invasive species on biodiversity and ecosystem services. The impact assessment protocol, EICAT (Blackburn et al. 2014; Hawkins et al. 2015) – and its adaptation to include socio-economic impacts, SEICAT (Bacher et al. 2017) – will be used to score impacts on biodiversity and ecosystem services of Invasive Species of Interest in five levels, from Minimal Concern to Massive. For example, provisioning ecosystem services are considered in SEICAT through impacts on “Material and immaterial assets” (e.g. agriculture, fisheries etc.), supporting ecosystem services are captured in EICAT mechanisms “Chemical, physical or structural impact on ecosystems” and cultural ecosystem services through SEICAT “Social, spiritual and cultural relations”. EICAT has the advantage that it has been adopted by the IUCN and, thus, our implementation at the continental scale can be used as a proof-of-concept for international adoption of the protocol.

Both EICAT and SEICAT (S/EICAT hereafter) classifications include estimations of uncertainty, but currently consider only detrimental impacts. In this project, we aim to adapt them to also quantify beneficial impacts (e.g. providing food for native species or humans, cultural values as recreational fishing and hunting) that are important to resolve management conflicts. We aim to measure positive impacts at a similar 5-point scale as detrimental impacts (e.g. by quantifying how much native species or human activities benefit from the presence of an invasive species), plus a 3-point scale uncertainty estimation (low-medium-high). Such consistency will facilitate the comparison of detrimental and beneficial impacts. We will test the adaptation using the Invasive Species of Interest selected in WP1 across a wide range of taxa and habitats. We will ensure that the selection of species for testing will include species with presumably detrimental and beneficial impacts.

Under the framework of this WP, we will model and map the potential impacts of Invasive Species of Interest on biodiversity and ecosystem services in Europe under current and future 2050 climate-change scenarios. Distribution modelling techniques already employed in Gallardo et al. (2017) will be used to correlate the presence of Invasive Species of Interest in Europe with the environmental conditions of their native and introduced range. We will use these models to predict the expansion of species under current and future 2050 scenarios, identifying regions of maximum concern because of their susceptibility towards invasion. SDMs will account for uncertainty in data availability through: i) bias-analyses of occurrence data; ii) modelling approach, through the use of ensemble models combining multiple modelling settings; and iii climate change forecasts, by exploring multiple IPCC scenarios.

Potential impacts of invasive species will be calculated by integrating species-specific S/EICAT scores with maps of predicted distributions and ecosystem services supply. To that end, we will build on the approach used by Nentwig et al. (2010) to assess the ecological and economic impacts of invasive mammals in Europe. First, we will gather from literature the existing maps reflecting ecosystem services (e.g. pollination, leisure, water purification, all available at European scale through the Joint Research Centre, https://data.jrc.ec.europa.eu/) and/or target assets (e.g. human population density in the case of invaders causing human health problems) that are directly affected by Invasive Species of Interest. Then we will combine distribution maps of species affecting a particular ecosystem service/asset to identify areas with high provision-high risk of invasion. As the impacts of invasive species are highly context-dependent, we will necessarily assume that the potential impacts of selected invaders are similar across Europe, a precautionary principle common in invasion biology. Local case studies (WP5) will better explore the spatio-temporal variability of impacts and allow comparing projections across scales.

Finally, we will use the Non-Native Risk Management (NNRM) scheme of Booy et al. (2017) to translate the general intervention scenarios developed in WP1 into species-specific scenarios. This scheme provides a structured evaluation of management options for current and future invasive species that, similar to S/EICAT, uses semi-quantitative responses and uncertainty scores to assess seven feasibility criteria: effectiveness, practicality, cost, impact, acceptability, opportunity and likelihood of re-invasion. We will finally compare the potential costs and benefits of alternative intervention scenarios in terms of biodiversity and ecosystem services.

Data, maps and models generated in this package will provide spatially-explicit estimations of the threats posed by IAS to biodiversity and ecosystem services in Europe and their potential evolution under a range of climate and management scenarios.

In this WP, we will identify range-shifting invasive plants that have not yet been reported in parts of the US but are projected to expand with climate change. This will help anticipating the threat posed by invasive species to biodiversity and ecosystem services under alternative intervention scenarios. We will first develop a database synthesising all ecological, agricultural, economic and human health impacts reported in the scientific literature and use S/EICAT protocols to evaluate impacts. Then we will capitalise on available occurrence data to model the potential distribution of ca. 100 range-shifting invasive plants. This approach is focused on emergent threats, whereas established species with the potential to become invasive under climate change, often called sleeper species (Crooks 2005), are out of the scope of this project.

This WP aims to advance the empirical understanding of invasive species impacts on biodiversity and ecosystem services and their context-dependency. At the local scale, a number of invaded and uninvaded sites across freshwater, terrestrial and marine habitats will be selected to measure impacts on biodiversity and ecosystem services (Table 1). In addition, physical removal experiments with minimal disturbance to non-target species will be used to follow changes in ecosystem properties after restoration. Our aim is to measure biodiversity and ecosystem services under the general assumption that restored sites will fall somewhere in between invaded and uninvaded treatments. This simple assumption has been rarely tested in the field, but plays an important role in differentiating major from massive impacts in S/EICAT protocols. Finally, we will use the software InVEST (https://naturalcapitalproject.stanford.edu/invest/) to spatially model the provision of ecosystem services, biodiversity and trade-offs at the local/regional scale (Nelson et al. 2009). All species sampled in WP5 will be modelled in WP3-4, evaluated with S/EICAT (WP2) and considered in the elaboration of management scenarios (WP1). In contrast to the continental evaluations of WPs 3 and 4, case studies will provide real on-the-ground information to test the accuracy of impact assessments like S/EICAT and to quantify the real costs and benefits of alternative management decisions. While case studies share a common work plan for the evaluation of impacts, the specific field methodologies differ depending on the habitat, invasive species and ecosystem services targeted in each case.

Figure 2.

Focal invasive species that will be investigated during InvasiBES in three local case studies planned in the Ebro River (Spain) (a) the blue crab (Callinectes sapidus) and (b) apple snail (Pomacea canaliculata); the French Alps lowlands (c) the Canadian goldenrod (Solidago canadensis) and (d) Himalayan Balsam (Impatiens glandulifera); and in marine habitats of California (e) the red-rust bryozoan (Watersipora subtorquata) and (f) the dark unicorn sea snail (Mexacanthina lugubris). (All photos licensed through CC BY-SA 3.0).

Case study 1-Freshwater ecosystems. We will focus on two recent invaders of the Ebro River and Delta (NE, Spain): the apple snail (Pomacea canaliculata Lamark, 1928) and the blue crab (Callinectes sapidus Rathbun, 1896). The apple snail, accidentally introduced in the area in 2010 (López et al. 2010), consumes vast amounts of rice and can devastate the flora and fauna of natural wetlands, with important impacts on food provisioning, nutrient cycling and primary productivity (EFSA Panel on Plant Health 2014). It is still spreading in the Ebro Delta despite the control and eradication measures implemented in rice paddies and the river channel (physical removal). The blue crab, also present in the Ebro Delta since 2013, is an omnivore able to feed on plants and animals, including apple snails, but it is also an important fishing resource with economic value. Therefore, this species has both negative (reduced biodiversity, changes in habitat structure) and positive (biological control, fishing resource) impacts on ecosystem services. Both species are being managed in parts of the lower Ebro River, which will facilitate the selection of invaded, uninvaded and restored plots under similar environmental and anthropogenic conditions. The work-plan includes 15 sampling stations per treatment (invaded, uninvaded and restored, total N = 45 per species) where we will determine the density and population structure of the invader. We will also take water, sediment and macroinvertebrate samples to calculate indicators of ecosystem services. The sampling campaign will be repeated at least twice (2019 and 2020) with the possibility of a third campaign in 2021. The impacts of the blue crab may be more difficult to assess because it is a highly mobile and territorial species. For this reason, we will consider using enclosures to further investigate changes in ecosystem services caused by the blue crab. With this information, we will finally employ the software InVEST to explore spatially how alternative intervention scenarios may affect ecosystem services at the local scale.

Case study 2-Terrestrial ecosystems. We will focus on two terrestrial plants that are highly invasive in semi-natural meadows and forest edges across Europe: the Canadian goldenrod (Solidago canadensis L.) and the Himalayan Balsam (Impatiens glandulifera Royle). The impacts on biodiversity and ecosystem services of these two invasive plants will be studied in detail in two nature reserves located in the French Alps lowlands: the "Reserve du Bout du Lac d’Annecy" and the "Marais de Giez". These two species and two natural reserves are particularly interesting because of their joint conservation and agricultural values. From the conservation perspective, these nature reserves are protecting hyper-sensitive habitats that harbour rare and protected species, which are now threatened by the presence of mono-specific stands of the two plant invaders. From the agricultural perspective, the eradication of the invaders is highly contested by farmers and beekeepers of the region who benefit from the high quantity of pollen they produce. It is thus important to clarify the real positive and/or negative impacts of Canadian goldenrod and Himalayan balsam on regulation (plant diversity and pollination), supporting (carbon storage) and provisioning (forage production) services. These impacts will be quantified from field observations along a gradient of invasion: from non-invaded sites to gradually more invaded sites, up to near-mono-specific stands. Eradication of these plants is not feasible in protected areas with limited application of herbicides. For this reason, we will explore the possibility of conducting laboratory experiments for physical removal.

Case study 3-Marine ecosystems. The choice of marine study species will be based on the results of our literature review, in which we will look for studies reporting distributions, abundances and per capita effects of range-expanding species and the > 250 alien marine species reported in California (https://www.wildlife.ca.gov/OSPR/Science/Cal-NEMO). Target species will be chosen based on their current occurrence in southern California and lack of previous studies, despite having high potential for impacts based on their abundance, range size, expected strength of community interactions and functional relationships to other impacting species (Parker et al. 1999; Thomsen et al. 2014). Potential candidates for this study include sub-tidal epibenthic invertebrates in the “fouling” community (such as the bryozoan Watersipora subtorquata d’Orbigny, 1852) and consumers, including the intertidal, range-expanding whelk Mexacanthina lugubris (G. B. Sowerby I, 1822). We will quantify impacts using field observations across gradients in invader abundance, field physical removal experiments and lab experiments to resolve community interactions and ecosystem dynamics, such as effects on water quality. Sampling sites will be chosen to share similar environmental and disturbance conditions to avoid confounding factors. These marine invasive species are likely to play supporting (habitat quality and biodiversity maintenance), regulation (carbon sequestration and water quality), provisioning (food production) and cultural (aesthetic, recreation and environmental education) roles in local ecosystems.

The project InvasiBES is designed to provide direct support to the implementation of national and international regulations of invasive species in Europe and the US, as well as to make progress towards accomplishing the targets of the Convention on Biological Diversity’s Strategic Plan for Biodiversity 2011–2020 (Aichi Target #9: “By 2020 […], priority species are controlled or eradicated and measures are in place to manage pathways to prevent their introduction and establishment”), the UN’s 2030 Agenda for Sustainable Development (Goal #15.8: “By 2020, introduce measures to prevent the introduction and significantly reduce the impact of invasive alien species on land and water ecosystems and control or eradicate the priority species”) and the EU Regulation 1143/2014 on IAS that aims to establish rules to prevent, minimise and mitigate adverse effects of invasive species on biodiversity and related ecosystem services. In particular, InvasiBES will contribute towards accomplishing the needs of these international regulations through the development of intervention scenarios that evaluate the cost of inaction and the cost-effectiveness and socio-economic aspects of invasive species management (WP1). By considering multiple scenarios of climate change (WPs 3 and 4), the project will also provide insights into how different levels of commitment to the Paris Agreement on Climate Change may affect the expansion of invasive species and their impacts on biodiversity and ecosystem services. Furthermore, InvasiBES will prioritise species listed under EU regulation for analysis (WP3) and so European and member state policy-makers and practitioners are expected to be especially interested in the project and will be invited to engage in participatory scenario planning. In the US, we will collaborate with the Northeast Regional Invasive Species and Climate Change (RISCC, https://people.umass.edu/riscc/) Management Network and the North American Invasive Species Management Association (NAISMA, https://www.naisma.org/) to support the regulatory listing of high-priority species identified in this project (WP4). At national and local scales, InvasiBES will provide the best-available evidence and models to evaluate the costs and benefits of invasive species management (WP5), thereby helping to make decisions that are relevant for the conservation of biodiversity and ecosystem services. Ultimately, knowledge and data produced in the framework of this project will support the implementation of national and international policies, evaluate strategies and actions to the improve management of invasive species, mitigate any potential negative effects and, ultimately, promote sustainability.