Ecology and evolution of invasive maple tree species

Biological invasions represent a major driver of the current decline of biodiversity worldwide and generate expensive management programs. Increasing attention has thus been devoted to the study of invasive species, which in tum has shown to provide valuable insights on ecological and evolutionary processes regulating species coexistence. A proper test of mechanisms promoting invasions requires nonetheless the use of a biogeographical approach between species native and invasive ranges. This approach has rarely been applied, especially for tree invasions, and Acer negundo L. and Acer platanoides L., native to North America and Europe, respectively, and reciprocally introduced into the other's range where they have spread, offer a perfect opportunity to employ it. Based on various methods such as population demography contrasts, meta-analytical statistics and quantitative genetics, this· project sought to highlight specific environmental factors, species functional traits and evolutionary processes that drive the success of maple tree invasion. The two species currently exhibit different stages of invasion throughout the geographical areas studied. While A. negundo has already aggressively invaded riparian habitats of Southern France, A. platanoides is present but not yet dominant in deciduous forests of Southern Ontario, Canada. Invasive genotypes of A. negundo exhibited pre-adapted plasticity to non limiting resource conditions and genetic differentiation in growth, above-ground biomass and phenology relative to native conspecifics while life history traits were only environmentally controlled in A. platanoides. This discrepancy may also be explained by a combination of different disturbance regimes between invaded habitats and different life history strategy between species. Frequent disturbances in riparian forests have favored the establishment of the fast-growing and highly competitive A. negundo while less disturbed inland forests have impeded dominance by the shade tolerant and dispersal limited A. platanoides. Overall, this project successfully demonstrated the importance of using various methods at the biogeographical scale to identify the contribution of multiple factors in the success of invasive species. It also illustrates that invasive trees have the potential to rapidly adapt to novel conditions and therefore represent appropriate models to assess the migration rate of tree populations and the role of adaptive plasticity and natural selection in a climate warming context.