EPPO Global Database

EPPO Reporting Service no. 07 - 2014 Num. article: 2014/139

Are non-native plants perceived to be more risky by horticulturists?

Horticultural trade has been identified as a particularly important pathway for the global entry and spread of plant species. In order to design effective risk management strategies, it is crucial to better understand what drives horticulturists’ risk perceptions. A large-scale survey was undertaken on perceptions of horticulturists (625 persons) in Switzerland to investigate risk and benefit for ornamental plant species, their attitude towards the regulation of non-native species, as well as the factors that are decisive for environmental risk perceptions and horticulturists’ willingness to engage in risk mitigation behavior.
Participants were presented with a list of 18 ornamental plant species and were asked to classify these plants as native or non-native. For all plants, a strong association was found between perceived origin and perceived environmental threat: the fraction of participants who perceived a plant to be risky was larger among those that classified the plant as non-native than those that classified it as native. On the other hand, the more important the plant was perceived to be for landscape design or for a participant’s business, the less risky the plant was evaluated. Though, the perception of origin may also have been influenced by the perceived riskiness of a plant species rather than the other way round. Willingness to engage in risk mitigation behavior was counteracted by the perception of benefits from selling non-native ornamental species. Many of the respondents displayed a positive attitude towards mandatory trade regulations and declared a willingness to engage in various voluntary actions to mitigate invasion risks from non-native ornamentals.
Among respondents, the perceptions of which ornamental plant species are native (or non-native) were often not congruent with the classifications proposed by the literature. Even among academic experts there exists a high diversity of alternative concepts of the non-native origin of a plant species in Europe. Such divergent perceptions of a key concept might hinder consensus building and weaken risk communication. The study highlights that horticulturists’ familiarity with a non-native species might lead to a cognitive conflict with the expert definition of the non-native origin of a species: a species that is characterized as ‘foreign’ by experts is ‘familiar’ to horticulturists due to their daily work. Thus, while the alien origin of a species can be an important scientific concept, it can be problematic in risk communication, especially for well-known and long-established species. In these cases, it might be more effective to focus communication on well-documented environmental impacts of harmful species rather than focusing on the ‘non-native’ status of species.


Humair F, Kueffer C ; Siegrist M (2014) Are non-native plants perceived to be more risky? Factors influencing horticulturists’ risk perceptions of ornamental plant species. Plos One 9, 12 pp.

Contact: Franzisca Humair, ETH Zürich (CH), E-mail;: f.humair@gmail.com