Leaf functional traits at home and abroad: A community perspective of sycamore maple invasion
Résumé
Understanding the mechanisms behind the successful invasion of alien plant species remains a significant research challenge in invasion ecology. There are surprisingly few cross-continental comparative studies which investigated interspecific trait differences between native and invaded ranges. Here, we compare leaf functional traits of sycamore (Acer pseudoplatanus L.), a deciduous tree species native to Europe and invasive in New Zealand (NZ), to co-occurring resident woody species in both the native and invaded ranges. We analyze a suite of 14 physiological traits on individuals growing either in shade or in sun light conditions. Despite similar environmental conditions, the leaf economics spectrum of forest communities is narrower in NZ than in France. Sycamore extends the leaf economics spectrum of the recipient community towards greater photosynthetic efficiency in the invaded range at a relatively low construction cost. This feature increases the competitive advantage of sycamore over native species. Biogeographic history likely has resulted in a native insular temperate forest community in NZ with unoccupied trait space along the leaf economics spectrum, making these communities susceptible to invasion by `pre-adapted' alien species, according to the Evolutionary Imbalance Hypothesis. Sycamore may thus successfully invade NZ evergreen forests simply because it fills a functional gap at the fast return end of the leaf economics spectrum, corresponding to a formerly empty niche. As a consequence, forest management can hardly extirpate the invasive alien tree.