Climate change and escaping ornamentals (WholsNext)

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 habitats and regions of Europe will most likely be affected by invasions, under climate change. All groups will use a common core set of 50 study species, and will work in close cooperation on complementary tasks along eight work packages. The contribution of my own working group to the overall project will be concentrated in the WPs 7 and 8 which are led by myself (WP7) and my co-worker Franz Essl (WP8). In WP7, we will use a spatially explicit plant spread model to simulate the potential invasion of the 50 study species across Europe. The simulations shall explore the effects of propagule pressure (~ restrictions of use), horticultural selection (= trait variation) and different climate scenarios on invasion risk. Models will be run for the area of the European Union (thus we will cover a climatic gradient from the Mediterranean to Northern Europe) up to the year 2100 under a set of at least three different climate-change scenarios. The effect of propagule pressure, and its interaction with climate, will be evaluated by varying the density of hypothetical invasion foci, i.e. the density of plantations within the potentially suitable climatic range. Simulation results will provide maps of potential future invasion levels for the 21st century in terms of the area occupied and of abundance. Species-specific and cumulative risk maps under different climate-change scenarios and under different possible restrictions of ornamental use can be derived therefrom. Finally, WP 8 is dedicated to the dissemination of project results to stakeholders and the general public. The main task within this WP will be the preparation and organization of a final project meeting that shall bring scientists and stakeholders / policy makers (horticulture, plant breeding industry, botanical gardens, horticultural societies, nature conservation managers, representatives of the European commission (DG ENV, EEA) and of national governments) together. The workshop will discuss project results against the general background of the consequences of deliberate plant species introductions in an era of global change.

Biological invasions and climate warming are two components of anthropogenic environmental change with potentially severe and interacting ecological and economic consequences. With respect to flowering plants, horticultural trade is the predominant pathway by which species are introduced to regions of the world where they are not native. In the European ornamental flora, many species stem from warm(er) climates. There is hence concern that climate change may foster alien plant invasions on the continent. The main objective of WhoIsNext was to explore these possible effects of climate warming on ornamental plant invasions in Europe and to identify possible future invaders and areas at particular risk. The project was a collaborative effort with contributions from teams at the Universities of Konstanz (lead), Grenoble, Tübingen and Vienna. Its objective was addressed by a combination of database, experimental and modelling studies. The Austrian subproject mainly focused on modelling work using data provided by experiments and database work conducted in the other subprojects to estimate necessary model parameters such as germination or seed production rates of individual species. In essence, the results of the Austrian subproject suggest that the climate predicted for the end of the 21st century will make considerable parts of Europe more suitable to more different non-native species already cultivated in European gardens and park. This is especially true for the northern and eastern regions of the continent. Among the 783 individual plant species modelled, variation was pronounced, however. In fact, a sizable minority will actually have lower chances of naturalization and spread in a warmer Europe, in particular those stemming from Mediterranean and boreal regions of the world. Generalizations from average trends to each individual species are hence impossible. We also did not find evidence that a warming climate may increase the risk that potentially invasive garden plants threaten native plants via hybridization. Finally, our modelling indicates that even those species that appear as winners under climate change may need considerable time to translate the more suitable climatic conditions into a larger distribution area because plant spread is an inherently slow process. As a corollary, the full consequences of a warmer climate for ornamental plant invasions in Europe may only become apparent after decades or even more than a century into the future. With respect to possible control measures, our results suggest that anticipatory management of future ornamental plant invasions by restrictions of use can be highly effective irrespective of how the climate develops. However, to be successful these restrictions need high level of compliance and will require well-thought combinations of different policy instruments beyond voluntary codes of conduct on the part of the horticultural industry, or simple reliance on consumer awareness.