Invited Research ArticleThe end of a myth: Solving the knotweeds invasion “problem”
Introduction
Scientific communities have alerted the public about the serious threats posed by biological invasions to biodiversity (Vitousek et al., 1997; Mack, 2001) and economic and human welfare (McNeely, 2001; Pimentel et al., 2000) for almost 20 years. The management of invasive species remains a major preoccupation of environmental managers (Andreu et al., 2009). The spread of the species is, in particular, considered worrisome. Linear transport infrastructures (roads, railways and waterways) are at the heart of this issue. Benedetti and Morelli (2017) demonstrated a significant spatial association between the hotspot distribution of alien plant species and road and railway density in Germany and Austria. This association confirms the conclusions of previous studies (Christen and Matlack, 2009; Brisson et al., 2010), showing that roadsides and rail networks are privileged colonization corridors.
This situation is all the more true for Fallopia spp. (common names: knotweeds, see photographs in Fig. 1), one of the most threatening species complexes worldwide. The species Fallopia japonica (Houtt.) Ronse Decraene, Fallopia sachalinensis (F. Schmidt ex Maxim.) Ronse Decraene and the hybrid Fallopia x bohemica (Chrtek and Chrtkova) are widespread invaders in Europe (Bailey and Wisskirchen, 2006) and in the whole world. It can be found in Australia, New Zealand, the United States, Canada, Chile, South Africa (for a map of known invaded geographical areas, see Martin, 2019). It even seems to pose problems for some managers in its area of origin (Japan). F. japonica and F. sachalinensis are rhizomatous perennial herbaceous plants originating from Asia (Bailey and Conolly, 2000) and colonizing riparian habitats and disturbed areas such as roads and railways (Tiébré et al., 2008; Rouifed et al., 2014). Rouifed et al. (2014) showed that, in a lowland area, the presence of a road within 10 m more than doubled the probability of encountering Fallopia spp. In a study conducted on three linear human-related infrastructures (Breton et al., submitted for publication), the authors identified 3.75, 15 and 11.29 patches on average with mean areas of 828, 1054 and 1175 m² per kilometer of invaded railways, waterways and roadways, respectively.
Three main mechanisms increase the dispersal of propagules of invasive species along roads (Bacaro et al., 2015): 1) roads are a source of disturbance, creating new environmental conditions (soils, light, drainage, etc.) that are suitable to ruderal and pioneer species; 2) roads favor the dispersal of propagules via air movement induced by car transit and transport of soil contaminated with plant fragments during construction works; and 3) roads facilitate colonization by invasive species by suppressing the growth or removing stands of native species. In some cases, natural disturbances can also be involved, such as floods that affect waterways and increase their colonization by invasive species (Tabacchi et al., 2005; Matsubara and Sakai, 2016). In addition, environments located along transport infrastructure are often highly managed environments. Certain management practices can also be a spreading mechanism. Thus, it has been reported that cutting could spread Fallopia spp. through stem fragments dispersal (Child et al., 2000). The role transport infrastructures play in the introduction of Fallopia spp. calls for their integration into management policy.
The strategies adopted to manage the environments located along transport infrastructure can have positive or negative effects on their colonization by Fallopia spp. These strategies depend, above all, on the perceptions of the managers charged with their management (hereafter called managers). Managers are charged with defining and implementing the plans for managing invasive species. They must prioritize and define actions in a context of limited financial and human resources (Andreu, 2009) and relative uncertainty (Liu et al., 2011) regarding the extent of the impacts induced by the species (Lavoie, 2017) and the most efficient – or at least the most desirable if one assumes that chemical treatment cannot be generalized to all environments – strategies of management to implement (Delbart et al., 2012; Jones et al., 2018; Rouifed et al., in press). Contexts of uncertainty are known to induce the most heterogeneous perceptions, as everyone tends to have his or her own perceptions depending on his or her personal experiences (Pahl-Wostl, 2006). Consequently, invasive species often induce a plurality of perceptions regarding the species itself and the “best” management to implement, which must be further analyzed. Many scientific studies have aimed to compare non-expert and expert perceptions of invasive species (Selge et al., 2011; Fischer et al., 2014). This focus is based on the premise that differences in knowledge influence the way the plant is perceived as well as the action to be taken with regard to it (McNeely, 2001; Fischer et al., 2014). For instance, Dickie et al. (2014) presented several examples of conflict surrounding the control or management of tree invasions, in which conflict has delayed, increased the cost of, or ceased projects aimed at invasive tree removal. Nevertheless, beyond perception differences between experts and non-experts, differences of perspective also exist among experts themselves. Previous studies therefore demonstrated that environmental managers rely largely on their own experience and advice from fellow manager and not on the most recent scientific knowledge (Matsek et al., 2014; Matsek et al., 2015). This situation undoubtedly creates differences in knowledge and expertise that can be translated in practice into different points of view on the action to be taken with regard to Fallopia spp. The management of transportation infrastructures involves a multiplicity of stakeholders who belong to a large diversity of professional structures. Individual and normative differences (i.e., induced by cultural differences between the management structures) in how management priorities are considered are likely to emerge (Moon and Adams, 2016) and to constrain effective outcomes (Friedel et al., 2011). Consequently, the questions of why and how to act – according to different managers – deserve study (Buijs and Elands, 2013).
Managers have tested numerous control methods, but none appear fully efficient and/or compatible with sustainable management (Delbart et al., 2012; Jones et al., 2018; Rouifed et al., in press). Some ineffective control actions are even suspected to promote the spread of species (Meier et al., 2014). Environmental managers perceive this context as worrisome (Rouifed et al., 2018). Vanderhoeven et al. (2011) determined that environmental managers in Belgium consider Fallopia spp. to be a problematic species. French environmental managers have produced numerous documents regarding Fallopia spp. and their management (Cottet et al., 2015). This documentation indicates a strong willingness to take action against Fallopia spp., but motivations of this action are only scarcely clarified. This clarification (why do I act here?) is however necessary to define efficient and targeted management. This observation led the authors of the article to conduct a survey to further comprehend transport infrastructure managers’ perceptions of Fallopia spp. in France. The survey sought to clarify the perceptions and induced management practices of Fallopia spp. of the managers charged with overseeing the environments along transport infrastructures (roads, railways and waterways) in France. This survey aimed to answer 4 questions:
- (1)
When? At what stage of the invasion - early or advanced - do managers feel the need to act? The authors hypothesize here, in line with some previous observations (Boyer, 2005), that managers feel a need to act too late, at a stage when the invasion can no longer be countered.
- (2)
Why? What are the reasons that motivate the managers to act against Fallopia spp.? The authors hypothesize that, in addition to the biodiversity issues often highlighted - insofar as the issues related to invasive species are generally raised by ecologists or naturalists – other reasons (e.g. safety, economical reasons) are given by managers working along transport infrastructures to act against Fallopia spp.
- (3)
How? What type of actions do managers implement regarding Fallopia spp., and are managers satisfied with their efficiency? The hypothesis is that managers focus primarily on eradication actions (rather than preventive actions) and that they mobilize many resources to achieve them, in vain.
- (4)
Who? How do perceptions differ according to the type of infrastructure that managers are in charge of? The authors hypothesize that the field of expertise significantly influences their perceptions and induced management practices (and therefore, when, why and how they act towards Fallopia).
Section snippets
An online questionnaire survey
To answer these questions, the authors conducted an online questionnaire survey. They administered the survey – between April and June 2016 – using the web-based application Google Forms. The survey comprised five parts: (1) A photoquestionnaire assessing the need for managing the vegetation located along transport infrastructures according to their degree of invasion by Fallopia spp. (2) Questions assessing the knowledge of the plant and its propagation processes. (3) Questions relating to the
Survey respondents
199 responses were collected. More than half of the responses came from road managers (n = 103). River managers were also well represented (n = 55), whereas railway managers were a minority (n = 15). This distribution was certainly observed because there are fewer of these managers in France than there are road or river managers. However, the distribution might also be a sign of a lower interest of railway managers in the issue of Fallopia spp. invasion compared to the interest levels of road
Issue-sensitive, motivated but exhausted managers
The survey demonstrated – as previous studies have (Vanderhoeven et al., 2011; Cottet et al., 2015; Rouifed et al., 2018) – that Fallopia spp. raises concern among managers. One exception was in this article highlighted: managers who were not able to identify and name Fallopia spp. from photographs did not express a strong need to manage the plant along transport infrastructures. However, this group only represents a minority of persons. Indeed, raising the managers’ awareness of the importance
Conclusion
The objective of the article was to study the perceptions and induced management practices of Fallopia spp. according to managers charged with the management of environments located along transport infrastructures (roads, railways and waterways) in France.
This work revealed a great heterogeneity of perceptions and management practices of Fallopia spp. according to managers' knowledge and their territory of action, whether roads, rivers or railways. They demonstrated different views to the
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We thank the Ministry of Ecological and Solidarity Transition (MTES) and the French Environment and Energy Management Agency (ADEME) for creating the Land Transport Infrastructures, ECOsystems and Landscapes (ITTECOP) research program and for funding our project (Dynarp Project). We also thank the Centre for Studies and Expertise on Risks, Environment, Mobility, and Urban and Country Planning (CEREMA) for our active collaboration in this project and, in particular, Virginie Billon and Joris
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