Photosynthesis and shoot allocation of amur honeysuckle and two native shrubs in deep shade

Aside from the larger question of which traits make introduced species invasive, there is the practical concern of understanding the ecology of established invasives. An ecological understanding of invaders allows us to better identify invasible habitats and know the advantages and disadvantages an invader holds in relation to natives. This gives insights on how the invader will interact with natives, and how it might fare over time. Throughout eastern North America Amur honeysuckle ( Lonicera maackii (Rupr.) Maxim) is a notorious invader of forests and forest edges. The species inflicts harm on individual species, communities, and ecosystem functions. Lonicera appears in forests across a continuum of light conditions. It possesses considerable shade tolerance, although the extent and nature of this trait has been rarely contrasted with native species. Lonicera appears to be less abundant and slower growing under the closed canopy of the forest interior. Forests on mesic sites, especially those with closed sugar maple ( Acer saccharum Marshall.) canopies or dense subcanopies have especially dim understories, perhaps posing a significant limitation on carbon gain in Lonicera . I compared the photosynthetic responses, leaf characteristics, and leaf area ratios (LAR) of Lonicera to two shade tolerant native understory shrubs, Asimina triloba Adans. (pawpaw) and Lindera benzoin Thunb. (spicebush). Lonicera had comparable light responses measured on a leaf area basis, but mass-based measurements show it is less efficient paying back carbon invested in leaf tissue. This arises because Lonicera does not adjust specific leaf mass downward to the level of Asimina and Lindera in deep shade. LAR is distinctly higher in Asimina and Lindera , suggesting higher rates of carbon gain in the native species. Because photosynthesis is only one of many other physiological, demographic, and community-level processes in play, we should not necessarily assume lesser success for Lonicera in deep shade.