Climate change and escaping ornamentals: Predicting the next generation of European plant invaders

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Most naturalized and harmful invasive alien plant species in Europe have been intentionally introduced for ornamental purposes. Thus, it is likely that important future plant invaders will be recruited from those ornamentals currently growing in our gardens. In addition, climate change might create increasingly suitable conditions for many ornamental plants, particularly those with origins in warmer regions. This may result in new invasions by formerly unproblematic ornamentals. Identifying such sleeping invaders before they escape and spread would be highly desirable, and would give stakeholders (e.g. invasive-plant managers, the ornamental plant industry) a head start in preventing future invasions. Our consortium of four groups will combine modelling with experiments to study a large number of ornamental plants and assess which of these species will most likely become invasive, and which regions of Europe will most likely be affected by invasions, under climate change. The study species will be selected by the consortium based on ornamental species lists, project-relevant criteria such as invasiveness elsewhere and data availability. All groups will use a common core set of 50 study species, including both hybrid and non-hybrid ornamentals, and will work in close cooperation on complementary tasks along eight work packages. In WP1, we will make a comprehensive overview of those ornamental alien species that are currently frequently grown in Europe as garden plants. We will use this database to test which species characteristics are associated with current naturalization success in Europe. Most importantly, this database will be used to select the core set of 50 ornamental aliens that we will include in the experimental (WP2, WP3, WP4) and modelling (WP5, WP6, WP7) working packages. In the experimental studies, we will test empirically how ornamental alien plants respond to warming (WP2) and changes in precipitation (WP3). In addition, WP3 will test how hybridization and genetic variation among cultivars contributes to invasion potential. Together with WP4, WP2 and WP3 will also provide parameters for the modelling studies, and ground-truth the findings of the latter. In the modelling studies, we will develop an invasion-simulation model (WP5), and use landscape-simulation modelling and a spread-modelling approach to assess the probability that certain ornamental species will establish at respectively the landscape (WP6) and European-wide scale (WP7). These models will also allow us to assess which types of habitats and which regions will be most vulnerable to invasions. The modelling studies will also help to design the experiments, and the modelling results will provide predictions for the tests in the experimental studies. Finally, in WP8, we will synthesize the results, and disseminate them to the relevant stakeholders, such as the ornamental-plant industry, garden-plant retailers, horticultural societies and policy makers.