We quantified trait-based ecological strategies of non-native, invasive woody species present in deciduous forests of North America, and contrasted functional syndromes of invaders to co-occurring native species. Our objectives were to 1) describe and contrast multivariate trait relationships of species from a single, widespread habitat type to those typical of the global plant economics spectrum; 2) test whether invaders are associated with a common set of distinguishing traits (‘invader syndrome’); and 3) identify whether natives and invaders are subject to similar functional tradeoffs. Since 2008 we have studied a common shade-garden population of 200 individuals of 76 shrub and liana species present in the understory of deciduous forests, including 44 native species and 32 non-native species documented as either naturalized (8) or invasive (24). Analyses include 68 continuous functional traits representing leaf metabolism and morphology, root function and anatomy, leaf and root chemistry, xylem anatomy, carbohydrate storage, foliar phenology, and DNA content.
Results/Conclusions
Principal components analysis identified two primary axes of trait differentiation across 76 species that accounted for 1/3 of all trait variation. Axis 1 (18%) was associated with instantaneous growth potential, separating species along a gradient of instantaneous carbon gain, size of metaxylem (early season) vessels, and determinate-to-indeterminate leafing behavior. Axis 2 (14%) separated species of large, thin, cheap, short-lived leaves from those of high leaf investment and lifespan, and, consequently, long leaf duration (days of live leaves per year). In contrast to patterns of the plant economics spectrum that often indicate tradeoffs in tissue protection (slow plants) versus tissue proliferation (fast plants), invasive species in our study had both high instantaneous growth potential and a longer growing season, particularly as a result of late autumnal senescence. No native species in our study showed this pattern. In addition, a decision tree analysis discriminated between native and invasive species with 93% accuracy using only two traits: leaf duration and nuclear DNA content, the latter of which indicates selection on maximum growth rate. Our study suggests the spread of woody invaders across deciduous forests of North America is largely due to their ability to maximize carbon and nutrient gain both at peak season and over a long growing season, with concomitant adaptations in root morphology (high specific root length), carbohydrate allocation (low storage), xylem anatomy (wide spring, narrow autumn vessels), and DNA content (fast mitotic rate).