Invasive plants: new study indicates how to prioritise species for management

Invasive alien plant species pose a threat to biodiversity, the economy and, sometimes, human health. The EU’s Biodiversity Strategy for 2030 commits to managing invasive species and halving the number of conservation Red-Listed species they threaten. The EU’s Invasive Alien Species Regulation commits Member States to restrict possible points of entry for invasive plants, as well as to improve detection and eradication of those already present, while also limiting their spread.

The new study presents a new approach to prioritising invasive plant species for management and selecting appropriate management actions. It is designed to counter several factors that increase the challenge of managing invasive plants. These include the high number of species that are continually introduced to new territories. Further, effective prevention and eradication can be delayed by time-consuming risk analyses of new introductions and unclear financial benefits of intervening in the early stages of an introduction.  

The Italian scientists devised the system based on the principles of eradication, control and monitoring. They originally designed it to present the European and Mediterranean Plant Protection Organization (EPPO), responsible for plant protection in the Euro-Mediterranean region, with a list of non-native invasive plants that are not yet subject to regulations in Italy and not included in the organisation’s prioritising and listing system. 

The species considered for control strategies included: 

• plants with at least one established population in Italy, but not included in the current list under the Invasive Species Regulation;
• plants with potential invasive behaviour and recognised impacts on ecosystems that had been reported in areas with similar climate and land use; 
• plants that experts consider as a threat to Italian biodiversity but are not included in EPPO lists. 

Following the initial selection process, they used a machine-learning method to calculate potential distribution in Italy for the different plant species. Additionally, they considered three different possible climate scenarios and the variation of climatic suitability for the plants.

To prioritise action against the plants, they grouped potential invasives by their suitability to Italian regions into three clusters. Further analysis was used to look at variability within each of the three clusters, after which they assigned a management priority to the groups. 

As a result of their efforts, the researchers identified 36 invasive non-native species suitable for inclusion by the EPPO. The analysis suggested that several species, including redroot pigweed (Amaranthus retroflexus) and Johnson grass (Sorghum halepense), are likely to be very invasive in Italy. Others, such as Western ragweed (Ambrosia psilostachya) and Jerusalem thorn (Parkinsonia aculeata), are likely to occur in restricted areas of the country. 

The work also allowed them to rank the plants in order of priority for action. Seven species posed a high threat in their early stages of invasion at a national level or in two biogeographic regions, such as the sacred lotus (Nelumbo nucifera) and fishpole bamboo (Phyllostachys aurea). Eradication was therefore considered a suitable management approach for these seven. 

The researchers recommended that four species that are already widespread in Italy, including black locust (Robinia pseudoacacia) and giant reed (Arundo donax), should be monitored. For the remaining 21 species, where they considered eradication to be no longer advisable, they recommended programmes of control and containment. 

When applied together, the team said that the methods used in their work, which was funded under the NextGenerationEU programme, could be replicated elsewhere in the EU, meeting the demand for new early-warning tools in the fight against invasive species. 

Decision-makers in other countries could also choose to add further criteria while using the same approach, further refining the system’s ability to assess risk and prescribe suitable management. 

Source: 

Lozano, V., Marzialetti, F., Acosta, A.T.R., Arduini, I., Bacchetta, G., Domina, G., Laface, V.L.A., Lazzeri, V., Montagnani, C., Musarella, C.M. and Nicolella, G., (2024) Prioritizing management actions for invasive non-native plants through expert-based knowledge and species distribution models. Ecological Indicators, 166: 112279.

To cite this article/service:

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.