Invasive plants: Climate is a determining factor

With the rise of European explorers and their discoveries of new geographic territories, five centuries ago, plant and animal species were moved by humans, accidentally or voluntarily, to places where they never existed before. Some species proliferated at the expense of local ones, menacing not only the equilibrium of the invaded ecosystems, but also causing serious socio-economic problems such as loss of crop productivity or an increase in allergies among the human population. However, these species provide the unique opportunity to understand ecological and evolutionary mechanisms that enable them to develop efficiently and rapidly in new regions.

For several years, Antoine Guisan, a professor in the department of ecology and evolution at UNIL, and his group have been studying the link between climate and plants' invasive potential within the framework of a project supported by the NCCR Plant Survival, a Swiss research network based at the University of Neuchâtel. "This study offers the strongest empirical evidence to date that climate is a determining factor in the geographic distribution of invasive plants," states Antoine Guisan.

Blaise Petitpierre, Olivier Broennimann and Christophe Randin, all members of his research group at UNIL, focus their interest on the climatic niche, which defines all the environmental conditions suitable to a species. They want to know whether or not plants conserve their original climatic niche when they colonise new territories. As for the ecologists, they are trying to highlight the morphological, physiological or ecological differences between invasive and local species. This is the area of expertise of Christoph Kueffer at the ETH Zurich and Curtis Daehler at the University of Hawaii in Monoa.

"We show that invasive plants succeed in climates analogous to those in their native ranges," add the authors of the article that appeared in the journal Science. Only seven of the fifty species that were studied do not follow this rule. The European native spotted knapweed (Centaurea stoebe), a model plant used for research at the NCCR Plant Survival, is part of those exceptions and shows a strong expansion of its niche in its introduced range in North America, especially in the Pacific North West. The reason for this expansion apart from native conditions is currently being studied by researchers at the University of Fribourg.

The authors of the article appearing in the journal Science have also shown that "invasive species, especially on the North American continent, have propagated themselves relatively quickly. One to two centuries was enough for them to occupy most of the climates that are suitable to them."

These results also provide valuable indications on the consequences of climate changes for the preservation of plant biodiversity. In fact, if invasive plants, which are generally considered to be particularly efficient colonisers, prove to be unable to proliferate in different climate conditions than the ones in their native place, then it is likely that plant species faced with strong climate variations in their native area would be faced with extinction if they do not manage to adapt to less favourable climatic conditions or migrate to follow their suitable ones.