A protocol to determine restrictions to use ornamental invasive alien plants
The varying definitions and concepts of what defines an invasive alien plant do not help scientists and horticulturists to agree upon which invasive species should no longer be planted. The lack of differentiation between alien species and alien species with the potential to cause a major detrimental impact may inflate the number of species listed, which may discourage horticulturists from taking action and lead policy makers to reject initiatives on invasive alien plants. In addition, lists of invasive alien plants are usually built on different criteria, therefore fueling debates and blocking the implementation of recommendations on invasive alien species.
To counter these difficulties, clear criteria for the listing of invasive alien plants should be agreed upon. An assessment protocol is proposed to determine whether a species can or cannot be grown for ornamental purposes. The particularity of the process is that it considers whether the species is a generalist (a species that can colonize numerous different habitats) or a specialist species (a species that can only colonize particular habitats), mainly by looking at the habitats invaded. Those generalist species able to spread to areas they may threaten should be prohibited. Specialist species with low distance spread abilities could still be planted in areas which are not connected to/close to areas at risk. The process allows benefits of an ornamental species to be taken into account.
To test this protocol, 20 species which are both recorded in the DAISIE database of alien plants in Europe and in French cultivated species catalogue (ASPECO) have been assessed using the proposed criteria.
A summary with the overall impact of the species (on human health, economic activities, biodiversity and ecosystem by taking the highest impact), whether the species is a generalist or a specialist, its spread ability, its overall benefits (in the reduction of the ecological footprint of plantations, on its landscaping use, or concerning economic or cultural aspects, by taking the highest benefit) are indicated in the table below. These factors along with knowledge of the plant lead to final recommendation for France from this protocol:
|
Species
|
Overall impact
|
Specialist/ generalist
|
Spread
|
Overall benefits
|
Recommendation for France
|
|
Achillea crithmifolia (Asteraceae)
|
Low
|
Specialist
|
Long distance
|
High
|
Can be grown anywhere, but remains on the observation list
|
|
Ailanthus altissima (Simaroubaceae, EPPO List of Invasive Alien Plants)
|
Medium
|
Generalist
|
Long distance
|
Medium
|
Do not grow
|
|
Baccharis halimifolia (Asteraceae, EPPO List of IAP)
|
High
|
Generalist
|
Long distance
|
High
|
Do not grow
|
|
Buddleja davidii (Scrophulariaceae, EPPO List of IAP)
|
High
|
Generalist
|
Long distance
|
High
|
Do not grow
|
|
Carpobrotus spp. (Aizoaceae, EPPO List of IAP)
|
High
|
Specialist
|
Long distance
|
High
|
Do not grow
|
|
Cortaderia selloana (Poaceae, EPPO List of IAP)
|
High
|
Generalist
|
Long distance
|
High
|
Do not grow
|
|
Erigeron karvinskianus (Asteraceae)
|
Low
|
Generalist
|
Short distance
|
High
|
Can be grown anywhere, but remains on the observation list
|
|
Eschscholzia californica (Papaveraceae)
|
Low
|
Generalist
|
Short distance
|
High
|
Can be grown anywhere, but remains on the observation list
|
|
Ipheion uniflorum (Amaryllidaceae)
|
Low
|
Generalist
|
Short distance
|
Medium
|
Can be grown anywhere, but remains on the observation list
|
|
Lippia canescens (Verbenaceae)
|
High
|
Specialist
|
Short distance
|
High
|
Can only be grown outside areas are at risk
|
|
Medicago arborea (Fabaceae)
|
Low
|
Specialist
|
Short distance
|
High
|
Can be grown anywhere, but remains on the observation list
|
|
Nassella trichotoma (Poaceae, EPPO Alert List)
|
Medium
|
Specialist
|
Short distance
|
High
|
Can only be grown outside areas at risk
|
|
Oenothera speciosa (Onagraceae)
|
High
|
Generalist
|
Long distance
|
High
|
Do not grow
|
|
Oxalis pes-caprae (Oxalidaceae, EPPO List of IAP)
|
High
|
Generalist
|
Long distance
|
Low
|
Do not grow and ensure that soil used in nursery is free from bulbils
|
|
Pennisetum clandestinum (Poaceae)
|
High
|
Generalist
|
Long distance
|
High
|
Do not grow
|
|
Pennisetum setaceum (Poaceae)
|
High
|
Generalist
|
Long distance
|
High
|
Do not grow
|
|
Pennisetum villosum (Poaceae)
|
High
|
Generalist
|
Long distance
|
High
|
Do not grow
|
|
Pittosporum tobira (Pittosporaceae)
|
Low
|
Specialist
|
Long distance
|
High
|
Can be grown anywhere, but remains on the observation list
|
|
Stenotaphrum secundatum (Poaceae)
|
Medium
|
Specialist
|
Short distance
|
High
|
Can only be grown outside areas at risk and their surroundings, sterile cultivar should be used.
|
|
Stipa tenuissima (Poaceae, EPPO Alert List)
|
Medium
|
Generalist
|
Short distance
|
High
|
Can only be grown outside areas at risk
|
Sources
Filippi O ; Aronson J (2010) Plantes invasives en région méditerranéenne: quelles restrictions d’utilisation préconiser pour les jardins et les espaces verts ? Ecologia mediterranea 36(2), 31-54.