Tue, Aug 03, 2021:On Demand
Background/Question/Methods
There are about 175 species of non-native invasive trees, shrubs, and woody vines in Eastern North America (ENA), spreading across a range of disturbed-to-intact forest habitats and accounting for nearly 40% of all ENA plant invaders. Why are so many invasive plants in ENA woody, and why do they have such large successional niches? I summarize the current understanding of woody invader functional strategies, focusing on recent findings of a functional syndrome in invaders that links carbon and nutrient foraging behaviors above- and belowground. I review the growth potential of ENA native and invasive species in different light and nutrient environments, and describe how invader growth advantages are associated with many other distinct traits, including foliar phenology, stem morphology, root anatomy, and the formation of mycorrhizas. I also discuss the need for additional studies to link invader functional traits to population dynamics to better understand the mechanics of invader spread.
Results/Conclusions Compared to native species, woody ENA invaders display a common set of functional traits implicated in fast growth when resources are abundant (e.g., light gaps) and high survival when resources are scarce. Enhanced carbon gain in invaders is due to several factors: they have higher rates of carboxylation in the higher light conditions of spring; they show higher quantum yield in the lower light conditions of summer; and they build more robust leaves of longer lifespan that continue carbon gain later into the season. Their stem anatomy permits high stomatal conductance in spring with large earlywood xylem elements, which narrow in latewood possibly to protect against late-season cavitation. Compared to natives, invaders show higher uptake rates of soil nutrients to enable fast leaf metabolism, enabled by a greater production of fine roots of high specific root length and lower dependence on mycorrhizas. This trait syndrome explains at a functional level the apparent plasticity of invaders to grow fast when resources are abundant but also tolerate relatively resource supply rates, enabling population growth across a range of successional habitats. Nonetheless, the origin of this syndrome remains elusive. Limited home-away contrasts to date suggest many invaders show similar functional attributes in their native and introduced ranges, with inconsistent evidence of enemy release. Other key knowledge gaps include the role of reproductive and dispersal traits, linkages of physiology to demography (particularly survival), and the role of habitat modification.
Results/Conclusions Compared to native species, woody ENA invaders display a common set of functional traits implicated in fast growth when resources are abundant (e.g., light gaps) and high survival when resources are scarce. Enhanced carbon gain in invaders is due to several factors: they have higher rates of carboxylation in the higher light conditions of spring; they show higher quantum yield in the lower light conditions of summer; and they build more robust leaves of longer lifespan that continue carbon gain later into the season. Their stem anatomy permits high stomatal conductance in spring with large earlywood xylem elements, which narrow in latewood possibly to protect against late-season cavitation. Compared to natives, invaders show higher uptake rates of soil nutrients to enable fast leaf metabolism, enabled by a greater production of fine roots of high specific root length and lower dependence on mycorrhizas. This trait syndrome explains at a functional level the apparent plasticity of invaders to grow fast when resources are abundant but also tolerate relatively resource supply rates, enabling population growth across a range of successional habitats. Nonetheless, the origin of this syndrome remains elusive. Limited home-away contrasts to date suggest many invaders show similar functional attributes in their native and introduced ranges, with inconsistent evidence of enemy release. Other key knowledge gaps include the role of reproductive and dispersal traits, linkages of physiology to demography (particularly survival), and the role of habitat modification.