A multi-level and multi-actor approach to risk governance: a conceptual framework to support policy development for Ambrosia weed control

Abstract

Invasive species such as Ambrosia (an annual weed) pose a biosecurity risk whose management depends on the knowledge, attitudes and practices of many stakeholders. It can therefore be considered a complex policy and risk governance problem. Complex policy problems are characterised by high uncertainty, multiple dimensions, interactions across different spatial and policy levels, and the involvement of a multitude of actors and organisations. This paper provides a conceptual framework for analysing the multi-level and multi-actor dimensions of Ambrosia management. Potential and existing public, private and public–private management strategies are identified to address the interests and needs of different actor groups across different levels. We conclude that policies that promote a mix of public and private Ambrosia management strategies may respond better to the needs and interests of different actor groups across different levels than a one-size-fits-all approach. However, multiple policy strategies need to be aligned in order to lead to synergies and spreading coherent messages to the public. Collaboration may enhance the likelihood of biosecurity management and risk governance of Ambrosia being adequately implemented and enforced.

Keywords:

• Common Ragweed
• innovation
• multi-scale
• participatory policy development
• public-private partnerships

Introduction

Invasive weeds threaten global food security, biodiversity, ecosystem services and human and animal health, and are considered as one of the key problems in agriculture and natural resource management (Kiley-Worthington 1980; Hulme 2006; Oerke 2006; Buckley 2008; Makra, Matyasovszky, and Deák 2014). Invasive weeds pose great biosecurity risks as they generally do not have natural enemies and spread rapidly. As a result, invasive weeds cause major environmental and economic losses (Groves and Willis 1999; van Wilgen et al. 2001; Sinden et al. 2004; Pimentel, Zuniga, and Morrison 2005; Setterfield et al. 2010). Given the biosecurity risks they pose (Crosson 1986; Reardon et al. 1997; Hulme 2006; Franks 2014), the management of invasive weeds requires coordinated policies. These policies refer to the practices, routines, technologies and modes of organising to protect human, animal, plant and environmental health from infectious diseases and invasive species (Heikkilä 2011; Reed and Curzon 2015). As the actions of individual actors or actor groups will determine the biosecurity status of a country or region and the risks faced by others, the control of invasive weeds may be considered as a ‘weakest link’ public good (Perrings et al. 2002; Oude Lansink 2011; Reed and Curzon 2015).

In light of the foregoing, invasive weeds and their control can be considered a complex problem (Hulme 2006; Schut, Klerkx et al. 2015; Schut, Rodenburg et al. 2015; Jordan et al. 2016), with resultant implications for biosecurity risk management and policy. Complex problems have multiple dimensions (biophysical, technological, socio-cultural, economic, institutional and political) that need to be analysed and addressed in an integrated way. Despite advances in control technologies, invasive weeds continue to be problematic because of the complex socio-cultural and institutional landscapes in which they occur (Epanchin-Niell et al. 2010). Furthermore, complex problems are characterised by the involvement of a multitude of actors and organisations (e.g. farmers and other rural landowners, government, the private sector, civil society, health organisations, researchers) (Funtowicz et al. 1999), who operate across multiple levels (national, regional, village, household) (Hulme 2006; Donaldson 2008; Schut et al. 2014). The diverse and sometimes competing needs and interests of the many public and private actors causing, or affected by invasive weeds problems present a challenge for designing and implementing coherent invasive weeds management policies.

Common ragweed (Ambrosia artemisiifolia, hereafter referred to as Ambrosia) is an example of a complex invasive weed problem that poses serious challenges to biosecurity management. Ambrosia is an annual species, native to Mexico, the United States and Canada. In Europe, Ambrosia has become invasive in more than 30 countries (Chauvel et al. 2006; Essl, Dullinger, and Kleinbauer 2009; Sikoparija et al. 2009; DAISIE 2014; Makra, Matyasovszky, and Deák 2014). Ambrosia possesses highly allergenic pollen that causes sensitisation of an estimated 15% (Germany, Netherlands, Denmark) to 60% (Hungary) of the allergic population, with annual medical costs of these allergies amounting to €110 million in Hungary and €88 million in Austria (Gerber et al. 2011). Furthermore, tourism can be affected if visitors avoid areas with high Ambrosia occurrence. Ambrosia is now also a major weed in European agriculture, especially in spring-sown crops such as sunflower, maize, sugar beet and soya beans. Yield losses alone have been estimated at €130 million/year for Hungary (Komives et al. 2006). Because of the taxonomic relatedness of sunflower and Ambrosia, herbicides are of limited use in this crop. The occurrence in crop systems facilitates the spread of Ambrosia throughout Europe by contaminating birdseed, other feeding mixtures (such as for game animals) and crop seed. As a response, European national and supranational government institutions have already financed several large research projects such as SMARTER, HALT-AMBROSIA and NOVARA. The SMARTER project aims – among other things – to bring together scientists from different disciplines and stakeholders at national and supranational level (essential for effective weed research according to Jordan et al. 2016). The significance of Ambrosia is also evidenced by the scientific opinions produced by the European Food Safety Authority (EFSA), both on the public and animal health aspects (EFSA 2010) and on the pest risk aspects (EFSA 2007a).

Invasive weeds such as Ambrosia pose risks to societies (health problems and reduced income from tourism and agricultural yields) that need to be governed. The concept of risk governance captures ‘the ways in which many actors (individuals, public and private institutions) deal with risks surrounded by uncertainty, complexity and/or ambiguity’ (van Asselt and Renn 2011, 432). Risk governance models may be classified as technocratic, decisionistic or transparent depending on the extent to which science, policy, economic actors and civil society representatives are involved in risk assessment and management (Mills et al. 2011). Technocratic and decisionistic models hold clear division of tasks, roles and responsibilities in which risk assessment is primarily seen as a responsibility for science (Pheloung, Williams, and Halloy 1999; Leung et al. 2002; Baker et al. 2005; Keller, Lodge, and Finnoff 2007; Buckley 2008; Bullock et al. 2010; Downey et al. 2010; Ferdinands et al. 2011), and risk management as the domain of public regulatory agencies and self-regulation in the private sector (Oude Lansink 2011). The dynamics of actor interactions across different levels tend to be overlooked, often leading to market and policy failures (Cook et al. 2010). For example, state-led command and control regulation is (1) costly and difficult to enforce, (2) does not provide incentives for actors to go beyond the minimum requirements set by the regulation and (3) is vulnerable to political manipulation and resistance by actors (Oude Lansink 2011). Adaptive management of biosecurity, connecting more with a transparent model to risk governance, could be more effective in terms of the supporting and streamlining of risk assessment and management efforts by different actors through time and space (Barker 2008; Cook et al. 2010; Foxcroft and McGeoch 2011).

In view of the complex character of Ambrosia and other invasive weed problems, the different fields of science relating to invasive weeds all indicate the importance of designing policy responses and actions at multiple levels and involving multiple actors. In the biosecurity management literature, actor mapping and mental model diagrams have been used to engage with actors regarding risks (Doohan et al. 2010; Gilmour, Beilin, and Sysak 2011; Mills et al. 2011; Reed and Curzon 2015). The risk governance literature has looked at engaging people at different levels in governance systems (e.g. municipal, national) (Johansson, Denk, and Svedung 2009; Soon and Baines 2012; Corin, McNeill, and Atapattu 2012). Plant health management science explores public and private sector responses to market failure (Oude Lansink 2011). Weed research literature has also focused on analysing and understanding interactions between, for example, the supranational, national and local levels (e.g. Gerowitt et al. 2003; Jordan et al. 2016) and has applied multi-actor approaches to better understand weed problems and develop locally adapted solutions (e.g. Jordan et al. 2002; Doohan et al. 2010). While these studies all point to the need to engage multiple actors across multiple levels in addressing invasive weed control, there have been limited attempts to develop a conceptual framework that can support the systematic identification, categorisation and analysis of the needs and interests of different actors across multiple levels, and relate that to incentives that drive their actions (Reed and Curzon 2015).

The scientific contribution of this paper is that we provide a conceptual framework that supports the systematic identification, categorisation and analysis of the needs and interests of different actors across multiple levels, and link this to incentives for engaging in individual and/ or collective invasive weed control. We deepen the framework for assessing public and private roles in plant health management developed by Oude Lansink (2011) in two ways: (1) by detailing multiple public and private affected, causal and managing actors and their interrelationships, and (2) adding multi-level perspective that explores the needs, roles and potential responsibilities of these actor groups in invasive weed control across multiple levels. This conceptual framework provides a basis for identifying public, private and public–private invasive weed management policies.

The societal contribution of this paper is that the framework developed, and its application to the case of Ambrosia in Europe, offers conceptual guidance for the design of coherent multi-level and multi-actor biosecurity risk management policies. The Ambrosia-related problems described above create great challenges for policy-makers responsible for the design and implementation of Ambrosia policy strategies. The fragmentation of policies and resultant management efforts across countries and the lack of internationally coordinated management could explain the rapid spread of Ambrosia across Europe in the past decades. An overview of (proposed) measures for controlling Ambrosia (Bullock et al. 2010, Annex 7) confirms that a multi-level, multi-actor approach has not been mainstreamed for Ambrosia management.¹

Conceptual framework

Affected, causal and managing actors

On the basis of work by Bullock et al. (2010) and Oude Lansink (2011), three clusters of policy-related actor groups for Ambrosia control have been identified. Ambrosia is causing damage to a wide range of affected actors such as farmers and other rural landowners, the tourism sector and allergy sufferers (Figure 1). The exact extent of the damage to the affected actors is an endogenous variable and is the outcome of actions of causal actors and managing actors. Causal actors are all those actors involved in activities that enhance the risk of the introduction, establishment and spread of Ambrosia. Policy actions by managing actors aim to decrease or prevent damage to affected actors. Managing actors themselves can manage Ambrosia directly, or they can manage it indirectly through policies and biosecurity regulations that seek to affect the behaviour of the causal actors so that the latter will undertake precautionary actions to reduce risks.

Figure 1. The mutual relationships and roles of causal actors, managing actors and affected actors.

The three clusters of actor groups are not mutually exclusive. As Figure 1 demonstrates, farmers and other rural landowners can be seen as both managing and affected actors. Similarly, tourists can both contribute to the distribution of Ambrosia (making them a causal actor) and experience the negative allergenic consequences of Ambrosia (making them an affected actor). Recognising this complexity, we base our analysis on the role that an actor is playing at a given point in time, rather than on the actor type per se.

Public good characteristics of Ambrosia control

Biosecurity management and risk governance options must address environmental, social and economic factors that influence causal and managing actors’ incentives to provide control measures (Larson et al. 2011). From an economic perspective, the optimal policy strategy to manage plants – such as Ambrosia – affecting society critically depends on the type of benefits generated by management. The economics literature identifies public goods and private goods (Samuelson 1954; Baumol and Oates 1988; Olson 2002). The first type is distinguished from the latter in two ways: (1) their consumption does not reduce the availability of the goods for others (non-rivalness) and (2) no one can be excluded from their consumption (non-excludability).

The non-rivalness of Ambrosia control implies that benefits for farmers, other rural landowners and allergy sufferers do not reduce the availability of the benefits of management for other actors. This condition is satisfied for most measures taken to prevent or reduce damage due to Ambrosia. For example, control that reduces pollen emissions benefits all allergy sufferers and the ‘use’ of it by one sufferer does not reduce the benefits available for other sufferers to ‘use’. Damage-reducing policy strategies taken by a managing actor provide benefits to affected actors that are also available to other affected actors. Such benefits include access to export markets, lower costs of weeding and lower health care costs because of lower pollen density.

In terms of Ambrosia control, non-excludability refers to the extent to which actor groups can be excluded from the benefits of control. Although some Ambrosia control policy measures can be classified as either pure public goods or pure private goods, some other policy measures have characteristics of both private and public goods. Following Oude Lansink (2011), Figure 2 demonstrates the dimensions of degree of rivalness and degree of excludability to indicate the public and private good characteristics of Ambrosia control.

Figure 2. Public and private good characteristics of Ambrosia control (adapted from Oude Lansink 2011).

Pure private goods are located in the upper left of the box while pure public goods are located in the lower right of the box. The bottom left part consists of the category of club goods. A key characteristic of club goods is that the benefits are (partially) excludable (Cornes and Sandler 1996), for example, by imposing fees or requiring club membership for full access to the benefits provided by the club.

The framework depicted in Figure 2 provides guidance for designing optimal management strategies and for identifying the key responsible public or private actor. With a low degree of rivalness and benefits that are only to a limited extent excludable, Ambrosia control is mostly classified in the lower part of Figure 2. Excludability ranges from low to high. Some benefits of Ambrosia control are restricted to the private domain of individual actors and are, to some extent, excludable. This holds for example for the benefits of on-farm weed control. Weed management undertaken in public parks or botanical gardens is classified as non-rival and excludable; therefore, it is a typical club good. Benefits from weed control undertaken in public areas such as roadsides and in nature reserves are not excludable, that is, the benefits are available for other actors. The same applies to measures taken to reduce the pollen load in the air and to weed risk assessment or biosecurity measures taken to prevent the entry, establishment and spread of Ambrosia. These measures are therefore classified as pure public goods in the bottom right part of Figure 2.

Multi-level analysis of actor groups’ needs, interests and responsibilities

Multi-level analysis is important for policy design as it facilitates the identification of actors across different levels and their interests and needs in the problem and the policy solution. First, it can provide the basis for balancing interests and bridging perceptions of different actor groups across different levels and for exploring feasible policy strategies to address complex problems (Giller et al. 2008). Second, it can contribute to increasing awareness about the interactions between levels, and their implications for management and policy (Schut, Leeuwis, and van Paassen 2013). Third, it can support the identification of mismatches between levels, for example when the objective is to address a transfrontier problem (such as invasive species) at the local policy level (e.g. village level) (e.g. Cumming, Cumming, and Redman 2006; Veldkamp et al. 2011).

Table 1 provides an inventory of causal, affected and managing actors across different policy levels: the individual, the country/subnational and the supranational level. These levels are closely interrelated and represent levels where the negative impacts of Ambrosia can be caused or experienced, and where policy strategies for managing Ambrosia problems can be developed. The supranational and country/subnational levels correspond with administrative or policy levels for collective decision-making (e.g. Cash et al. 2006), whereas the individual level captures how single actors can make decisions that may cause, or contribute to managing, Ambrosia problems. The needs, interests and responsibilities of the different actor groups across different levels are further elaborated in the following three subsections.

Table 1. Inventory of causal, affected and managing actors across different target levels (based on Bullock et al. 2010).

Level targeted	Causal actors	Affected actors	Managing actors
Supranational	• International (bird) seed producers and retailers	• International seed businesses	• Supranational organisations such as the European Union (EU) • International research institutes
Country/subnational	• Trading companies • Seed producers and retailers • National (bird) seed producers and retailers • Botanical gardens and national parks • Gardening companies • Public road workers	• Trading companies • Governments • Health insurance firms • Botanical gardens and national parks • Farmer and rural communities • Garden centres • Gardening companies • Tourist sector	• Local and regional government institutions • National and regional health services • Nature conservation organisations • Allergy-sufferer interest organisations • Botanical gardens and national parks • Construction companies • Gardening companies
Individual	• Farmers and other rural landowners • Tourists • Researchers	• Farmers and other rural landowners • Citizens • Tourists	• Farmers and other rural landowners • Citizens

Supranational level

Actors at the supranational level can have a considerable impact, in terms of both the spread of Ambrosia and of the development and implementation of policies for managing it. The inclusion of Ambrosia in seed or birdseed mixtures, for example, can contribute significantly to its international distribution. Economists consider this unintended entry pathway for invasive species as a negative externality of trade (Cook et al. 2014). The discovery of such seed contamination may result in direct liability, bad publicity, cleaning up of seed systems, and trade or export limitations that may result in huge costs for seed multinationals. Similarly, actors at the supranational level may have the highest impact in terms of developing and enforcing management strategies. Supranational bodies, such as the EU, can raise awareness and develop, coordinate and enforce biosecurity policies for Ambrosia control. Meteorological and other types of research organisations can reduce risk and uncertainty by applying models to predict seed distribution patterns, report Ambrosia spread and explore the effectiveness of different types of Ambrosia control strategies. International nature conservation organisations can support transfrontier policies to manage Ambrosia and raise awareness of Ambrosia through training and education. These measures at the supranational level are public goods located at the bottom right of Figure 2, and failure to implement them will increase the risk for other countries.

Country/subnational level

At the country and the subnational level, botanical gardens, trading companies, and (bird) seed producers and retailers are the most important causal actors. Ambrosia can be in the live collections of botanical gardens, and (bird) seed trading companies may be trading in contaminated seed mixtures containing Ambrosia; this may result in trade embargos as an extreme measure. Among the affected actors are governments, who are likely to carry some of the costs involved in Ambrosia prevention and control, and reduced revenues from tourism can have an additional negative impact. Health insurance firms may experience additional costs incurred from compensating treatments for allergy sufferers, and public gardens or nature reserves may experience reduced visitor numbers and revenues, and extra costs for eradication. Ministries and other government departments are among the key managing actors at the country level, especially with regard to the implementation of preventive phytosanitary measures. Other managing actors at the country level include farmer unions, researchers and health service providers who are instrumental in monitoring Ambrosia problems and facilitating communication, raising awareness and mobilising support for effective Ambrosia control. Examples include the smartphone app introduced by the Dutch Food Safety Authority to report Ambrosia (http://www.pollennieuws.nl/archieven/alsemambrosia/ambrosia_app/) and the SMARTER consortium funded by the European Union (see http://ragweed.eu/app/). Furthermore, the International Ragweed Society proclaimed an International Ragweed Day to be held on the first Saturday of the summer in order to increase understanding and awareness of the Ambrosia problem. The day was chosen because it is early in the plant’s growing season and therefore gives enough time for preparations and actions (Ries 2015).

At the subnational level, garden centres and/or companies can contribute – often unknowingly – to the introduction and spread of Ambrosia by using contaminated planting materials. Garden centres and/or companies can face reduced sales, liability claims and an increase in costs for clean planting material and eradication of Ambrosia. The reputation of regional tourism can be affected, resulting in reduced revenues for the tourism sector. Regional authorities, such as provincial and municipal governments, implement and enforce Ambrosia control policies on the ground. They also play an important role in raising awareness and communicating Ambrosia’s negative impacts for the public. Private sector actors, including construction companies, garden centres and gardening companies, can play reporting, monitoring and awareness-raising roles.

Individual level

The affected actors at the individual level include citizens, farmers and other rural landowners who suffer from the negative impacts of Ambrosia through allergenic or other health consequences and related costs, extra costs involved in Ambrosia control or reduced farm yields. Causal actors such as citizens, farmers and other rural landowners can accidentally contribute to Ambrosia distribution by spreading Ambrosia seeds on either their boots or their clothes, or through the movement of contaminated (farm) machinery. Individual farmers, rural landowners, volunteer naturalists, gardeners, hikers and tourists can play an important role as managing actors through their contribution to Ambrosia policy implementation e.g. by uprooting Ambrosia and avoiding the spread of Ambrosia seed. While individual control efforts are carried out as a private good (top left of Figure 2), the benefits of control are a public good and the biosecurity risk faced by the wider society is influenced by the control measures taken by each actor.

Towards multi-level, multi-actor policy strategies for Ambrosia control

The identification of key causal, affected and managing actors across different levels provides a basis for tailoring policy strategies for Ambrosia control. Bullock et al. (2010) categorise strategies for Ambrosia control into: (1) eradication, (2) monitoring, (3) prevention and (4) awareness raising. In this section, we first discuss strategies that can foster public, private and public–private management of Ambrosia across various levels. This is followed by a discussion on how the different strategies could be integrated towards multi-level, multi-actor policy strategies.

Adaptive management strategies for Ambrosia control

Public sector management options

Table 2 shows that opportunities for public sector management options are found at the supranational and the national level. These comprise public good activities that are located on the bottom right of Figure 2, and for which private sector actors do not have the incentives to carry out. At the supranational level, only prevention measures are available as a risk management option. Existing policy measures entail the phytosanitary regulations ruling the trade in plants and plant products (i.e. the WTO Sanitary and Phytosanitary Measures) (MacLeod et al. 2010). Under this policy, trade in seeds that are contaminated with Ambrosia seeds can be prohibited. National health services across the world have been assigned the task of monitoring through border inspections of imported plants and plant products (FAO 1997, 2011). A key challenge with the border inspections is the administrative complexity associated with inspecting rapidly increasing volumes of imports in the form of containerised cargo (Levine and D’antonio 2003; Magarey, Colunga-Garcia, and Fieselmann 2009). There are also tensions between the promotion of free trade (for example within the EU) and the governance of biosecurity risks within a country. International protocols that view the management of biosecurity risks as a technical project ignore these complex geopolitical processes (Weiss, Thurbon, and Mathews 2006; Mather and Marshall 2011; Maye et al. 2012). Determining the Acceptable Level of Protection thus requires negotiations to ensure the welfare of trading partners (Cook et al. 2014).

Table 2. Management strategies at different levels.

Level targeted	Public sector management options	Public–Private management options	Private sector management options
Supranational	• Prevention
Country/subnational	• Eradication • Monitoring • Prevention • Awareness raising	• Eradication • Monitoring • Awareness raising	• Monitoring • Prevention • Awareness raising
Individual			• Eradication • Monitoring • Prevention

Measures to monitor the presence of Ambrosia plants and seeds at national and subnational level are usually implemented through regulation that imposes mandatory monitoring to be performed by farmers and agribusiness firms in the supply chain (Bullock et al. 2010). National plant health services or research institutes may also be responsible for monitoring the presence of Ambrosia plants. Currently, several public health institutions such as public health services and hospitals are undertaking regulatory pollen monitoring (as stated on Weatheronline.nl 2015). Public institutions at the national and sub-national level can also engage in direct actions to prevent the spread of pollen by activities such as mowing Ambrosia-infested roadsides and natural habitats before the plant flowers.

Awareness raising will contribute to enhanced support among actors for the implementation of measures to control Ambrosia, as, through awareness raising, actors will have a better understanding of the risk it poses (Genovesi 2005; Thompson and Ziska 2014; Wallace and Bargeron 2014). It is clear though that awareness is a scarce resource and that activities to raise awareness for Ambrosia have to compete with awareness activities for other urgent problems. Nevertheless, Ambrosia could have a fair chance of standing out, in particular because its pollen pose such clear health problems to allergy patients. Exemplary for this is the extensive media coverage that was given to the introduction of an App to report Ambrosia in the Netherlands and the subsequent increase in the number of Ambrosia reportings. Risk perception plays a major role in how the actor groups perceive Ambrosia and the (individual and collective) willingness to invest time and other resources in controlling it (García-Llorente et al. 2008; Selge, Fischer, and van der Wal 2011; Maye et al. 2012; Ilbery et al. 2013; Touza et al. 2014; Tassin and Kull 2015). Awareness raising may increase the effectiveness of prevention, monitoring and eradication strategies in the public and the private sector. It entails activities aimed at informing citizens, private companies, farmers and other rural landowners about the adverse consequences of Ambrosia plants and pollen. Such activities include national and local (mass) media campaigns (e.g. Bullock et al. 2010, Annex 7) or the creation of opportunities for citizen science through real-time monitoring (Wallace and Bargeron 2014; Karpouzoglou et al. 2015) of invasive species, as indicated in the subsection Country/Subnational Level. Awareness is a prerequisite for engaging in (collective) prevention, monitoring and eradication. However, it needs to be complemented by interventions that:

•	Install deeper reflection on causal mechanisms perpetuating the problem and the role of actors therein;
•	Improve access to knowledge (e.g. about what are effective management strategies);
•	Lead to new institutional arrangements (e.g. incentives that stimulate [voluntary] action);
•	Increase belief in entities’ own capacities (e.g. that individuals or group efforts can have an impact) and;
•	Enhance trust in the social environment (e.g. that ‘others’ are also committed to addressing the problem) (van Mierlo, Arkesteijn, and Leeuwis 2010; van Mierlo, Leeuwis et al. 2010; van Mierlo, Regeer et al. 2010; van Asselt and Renn 2011).

Private sector management options

Management of Ambrosia in the private domain is more likely to be a private good (top left of Figure 2) where individuals are self-interested in managing Ambrosia. Policy strategies ultimately focus on supporting and creating awareness and incentives for actors to engage in eradication (weed control), prevention and monitoring within their ‘management mosaics’ (Epanchin-Niell et al. 2010). Farmers may take preventive measures, such as cleaning machinery and clothes to prevent the spread of Ambrosia seeds, and to buy cereal seeds that are certified as free of Ambrosia seeds. Similarly, citizens may manage Ambrosia through eradication of the plant on their private land. Ambrosia control on private landholdings by citizens, farmers and other rural landowners is sufficient if the private optimal level of management coincides with the socially optimal level. This condition would be satisfied if the presence of Ambrosia on private lands did not cause negative externalities for, for example, allergy sufferers, or if the Ambrosia seeds did not spread outside these private landholdings. Management of Ambrosia in construction areas is also a private good. In this case however, it is unlikely that construction companies will sufficiently manage Ambrosia without additional incentives (Bullock et al. 2010) as the companies themselves will not suffer from the presence of Ambrosia. To the best of the authors’ knowledge, there is currently no regulation for controlling or eradicating Ambrosia on construction sites in the EU (see also Starfinger, Sölter, and Verschwele 2014). Botanical gardens are typical club goods, and voluntary Ambrosia eradication by the owners can be an optimal management strategy, provided that the presence of Ambrosia reduces the value of the gardens to visitors now or in the future and that their private optimal level of management coincides with the socially optimal level (taking the negative consequences for allergy sufferers into account). There is a risk, though, that the benefits of Ambrosia management by the owners will not outweigh the costs. Consequently, owners may not have a sufficient incentive to control Ambrosia to a socially optimal level. In that case, additional policy directives and regulation from government bodies will be required, such as mandatory control of Ambrosia on private land. Also here, despite the likely need for a policy intervention, there seems currently no attempt to implement a mandatory control of Ambrosia in botanical gardens.

Public–private sector management options

Public and private sector management strategies may become more effective when combined with public–private sector initiatives. Organisations representing allergy sufferers or nature conservation organisations may target their members through awareness campaigns, thereby indirectly enhancing the effectiveness of Ambrosia eradication, prevention and monitoring by private and public sector actors. Nature conservation organisations can mobilise volunteers for eradication and monitoring activities in nature reserves or other public areas. Similarly, allergy-sufferer organisations may target their members to contribute to monitoring campaigns, for example by installing and using the online and mobile phone Ambrosia Application (as reported on Pollennews 2015). The public sector may make provisions to compensate affected farmers and other rural landowners who might otherwise be tempted to withhold information about their infested fields to avoid containment or eradication strategies that involve destruction of their crops or trade restrictions (Oude Lansink 2011; Cook et al. 2014).

Mechanisms to support the adaptive management of biosecurity risks

The policy strategies and control options discussed in the previous sections are closely interrelated. For example, the design of public prevention strategies and regulation at the supranational level needs to provide a degree of flexibility to be adapted to the country-specific context in which these strategies need to be implemented and enforced. In countries with a high level of agro-ecological or socio-organisational diversity, an adaptive approach to biosecurity management and risk governance implementation at the subnational level needs to be considered (Johansson, Denk, and Svedung 2009; Cook et al. 2010; Foxcroft and McGeoch 2011). Other studies have shown how the operationalisation of supranational policies at national, subnational and local level is essential for policies to be effective and meaningful (Sumberg 2005; Schut and Florin 2015). Important linkages can also be identified between the (sub)national and the individual level. Policies and (social) media that aim to raise awareness at national level, for instance, will greatly influence public opinion. Combined with concrete investments in improved access to knowledge and new incentive systems (see van Mierlo, Leeuwis et al. 2010), this will largely determine whether and how individuals or communities at more local levels will engage in action (e.g. in eradication, monitoring and prevention of complex problems). Consistency in terms of the type of information being disseminated and the type of control options being promoted is essential for the development and implementation of coherent multi-level risk governance strategies. Policy-makers have a key role and responsibility in complementing private and community level actions (Mansbridge 2014). Ultimately, the right balance between individual (private) action, community self-regulation, and state-led command and control regulation will depend on the specific governance context and incentives for actors (Soon and Baines 2012; Ervin and Jussaume 2014).

Synergies need to be explored not only across different levels, but also between public, private and public–private control options. This is necessary to prevent the spread of contradictory messages to the public (e.g. about the most effective Ambrosia control strategy). For example, in regions where Ambrosia is problematic, causal, affected and managing actors could all benefit from aligning prevention and control strategies, such as the timing of Ambrosia eradication activities. Joint monitoring and awareness-raising activities can enhance policy impact and might also reduce costs as suggested by Oude Lansink (2011) and Marshall et al. (2016).

For effective multi-level and multi-actor collaboration, the continuous involvement of public and private actors in describing and explaining problems and exploring and designing policy strategies is crucial (Kropff, Bouma, and Jones 2001; Klerkx, Aarts, and Leeuwis 2010). Advantages of such an approach in risk governance are that (1) different actor groups provide diverse insights about the biophysical, technological and institutional dimensions of the Ambrosia problem (Crosson 1986) and the types of solutions that are technically feasible, economically viable, and socio-culturally and politically acceptable for the key actors across levels (Schut et al. 2014); (2) through joint analysis and exploration of policy options, actor groups become more aware of their fundamental interdependencies and the need for concerted action to reach their objectives (Leeuwis 2000); (3) actor groups are more likely to support the solutions when they have been part of the decision-making process (Faysse 2006), and this is essential for their implementation and enforcement; and (4) information flows between actors at local, national and international level reduce uncertainty (Waage and Mumford 2008; Magarey, Colunga-Garcia, and Fieselmann 2009; Cook et al. 2010; van Asselt and Renn 2011).

Recent practical experiences from such a multi-actor, multi-level (parasitic) weed management project are summarised by Rodenburg et al. (2015). These scholars highlighted that, upon identification of a specific problem at any level (e.g. the farm level), one should critically zoom in and out to consider the broader context and to critically assess whether and for whom the problem is sufficiently relevant. Rodenburg and colleagues conclude that this process is crucial for the identification and assessment of the problem as well as for finding solutions (2015, 337). However, there are also trade-offs between engagement with actor groups that have the greatest power and influence over biosecurity outcomes vis-à-vis inclusion of marginal actors as equals in the decision-making process (Mills et al. 2011; Reed and Curzon 2015). In addition, effective communication of biosecurity risks becomes more complicated when actors have different levels of knowledge and handle risk and safety on the basis of diverse rationalities (Johansson, Denk, and Svedung 2009). Ensuring accountability and establishing trust between different actors at different levels are also complex activities (Gilmour, Beilin, and Sysak 2011; Drott et al. 2013). As proposed in both the risk governance literature and the literature on natural resource management and agricultural innovation, the establishment of platforms or other ‘spaces’ where different actor groups from different levels are represented could provide an interesting opportunity for on-going debate, negotiation and collaboration for effective Ambrosia control (following Röling 1994; Foxcroft and McGeoch 2011; van Asselt and Renn 2011; Kilelu, Klerkx, and Leeuwis 2013). However, the success of such platforms depends to a large extent on their institutional embedding and on whether or not different actor groups see their needs, interests and incentives reflected in the problem definition and proposed solution pathway (Schut et al. 2016).

At present it seems unlikely that an internationally coordinated platform to eradicate and prevent further spread of Ambrosia across will be established. The reason is that this will require the consent of a multitude of local, national and supra-national governments in countries and regions that are not all equally jeopardised by Ambrosia. An additional complexity is that the measures imposed will likely also target the free movement of plants and plant products. Hence, any measure that will do so will be under scrutiny of WTO regulations. The EU has the option though to place Ambrosia on the list of quarantine organisms. These are defined as ‘plant pathogens that are not yet present in the EU, or are present but not widely distributed, and deemed by EU legislation as being harmful to plant health’. When placed on the list of quarantine organisms, the EU can impose policy measures aimed at preventing the introduction and further spread of such organisms. Moreover, every EU country will be obliged to eradicate Ambrosia in its territories. Earlier attempts by Poland and Lithuania (EFSA 2007a, 2007b) failed among others because Ambrosia was already widely distributed in these countries.

Conclusions

The conceptual framework provided in this paper provides a basis for more systematic understanding of the needs, interests and responsibilities of different types of actors across different levels in risk governance. It shows that combined multi-level and multi-actor analyses are essential to understand the biosecurity problems (such as invasive weeds) and explore integrated policy strategies for biosecurity management and risk governance. Such analyses can support the development of policy strategies that are locally adapted, coherent across different levels and acceptable for different actor groups. This paper provides a starting point for reflection by policy-makers on how a broad mix of public and private biosecurity management strategies, rather than predetermined and fixed roles and responsibilities, may better respond to the different (and changing) needs, interests and incentives of different actor groups across different levels. In doing so, it supports adaptive management of biosecurity challenges to increase efficiency and cost-effectiveness in the coordination of risk assessment and management efforts of different actors through time and space.

For the case of Ambrosia, control on farmers’ fields and citizens’ properties is a public good and can be delegated to individuals to the extent that private optimal levels coincide with socially optimal levels. This is more likely the case for the control of the Ambrosia plant and less likely the case for the spread of Ambrosia pollen. Ambrosia control in public areas has the characteristics of a public good, in terms of the presence both of the plant and of the pollen. Eradication, monitoring and prevention of Ambrosia plants in public areas and preventing the spread of pollen from plants in public areas are the prime responsibility of public institutions. The effectiveness of management can benefit from awareness-raising activities mobilising the help of citizens and increasing support for measures imposed upon individuals and the private sector.

As a ‘weakest link’ public good, the biosecurity status of the EU as a whole will depend on the weakest member state. Policy strategies developed at the supranational level need to be operationalised at the (sub)national level so that concrete management options, and the indicators to assess them, correspond with local realities faced by different groups of actors. Furthermore, alignment of management strategies at the (sub)national level could lead to synergies in terms of reducing costs and enhancing the spread of coherent messages to the public. Collaboration between groups of actors representing different levels may enhance the likelihood of such coherent multi-level policy strategies being enacted through appropriate, adaptive biosecurity management and risk governance practices.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Perhaps with the exception of eradication, which does include individual farmers, other rural landowners and (sub-)national government actors (Bullock et al. 2010, Annex 7).