Fast but steady: An integrated leaf-stem-root trait syndrome for woody forest invaders.

Successful control and prevention of biological invasions depend on identifying traits of non-native species that promote fitness advantages in competition with native species. Here, we show that, among 76 native and non-native woody plants of deciduous forests of North America, invaders express a unique functional syndrome that combines high metabolic rate with robust leaves of longer lifespan and a greater duration of annual carbon gain, behaviours enabled by seasonally plastic xylem structure and rapid production of thin roots. This trait combination was absent in all native species examined and suggests the success of forest invaders is driven by a novel resource-use strategy. Furthermore, two traits alone-annual leaf duration and nuclear DNA content-separated native and invasive species with 93% accuracy, supporting the use of functional traits in invader risk assessments. A trait syndrome reflecting both fast growth capacity and understorey persistence may be a key driver of forest invasions.

Functional shifts in leaves of woody invaders of deciduous forests between their home and away ranges.

Temperate forests are widely invaded by shade-tolerant shrubs and trees, including those of Eastern North America (ENA). However, it remains unknown whether these invaders are 'preadapted' for success in their new ranges due to unique aspects of their evolutionary history or whether selection due to enemy release or other postintroduction processes have driven rapid evolution in the invaded range. We sampled leaf traits of populations of woody understory invaders across light gradients in their native range in Japan and in their invaded ENA range to examine potential phenotypic shifts related to carbon gain and nitrogen use between ranges. We also measured leaf traits in three co-occurring ENA native shrub species. In their invaded range, invaders invested significantly less in leaf chlorophyll content (both per unit leaf mass and area) compared with native range populations of the same species, yet maintained similar rates of photosynthesis in low light. In addition, compared with ENA natives, ENA invaders displayed greater trait variation in response to increasing light availability (forest edges, gaps), giving them a potential advantage over ENA natives in a variety of light conditions. We conclude that, for this group of species, newly evolved phenotypes in the invaded range are more important than preadaptation for their success as shade-tolerant forest invaders.