Tolerance of alien plant species to extreme events is comparable to that of their native relatives

In addition to increases in temperature and CO₂, other features of climate change, such as extreme events and short-term variations in climate are thought to be important. Some evidence indicates that invasive plant species might benefit from climate change via these features. However, apart from theory-based predictions, knowledge of the tolerance of invasive species to short-term climatic stress is very limited. We investigated whether three naturalized alien plant species in central Europe, Ambrosia artemisiifolia, Hieracium aurantiacum and Lysimachia punctata perform better under stressful conditions than comparable native species. A greenhouse experiment with a fixed stress sequence of frost, drought and water logging was set up. We applied this stress treatment to two life history stages (seedling and adult plants), plants grown in monoculture (mild intraspecific competition) and in a highly competitive setting with intra- and interspecific competition. Whilst small differences in plant responses were detected the alien species overall were not more tolerant to stress. The responses of alien and native congeners/confamilials to stress in all treatments (monoculture, competition, adult, seedling) were similar, which indicates that stress thresholds are phylogenetically conserved. All species were more vulnerable to stress at the seedling stage and when subject to competition. Our data indicates that results obtained from experiments using onlymonocultures and one development stage are not appropriate for drawing generalizations about lethal thresholds. Moreover, rather abrupt species-specific thresholds exist, which indicates that a prediction of species responses based on just two stress levels, as is the case in most studies, is not sufficient.