Defoliation by a native herbivore, Omphalocera munroei, leads to patch size reduction of a native plant species, Asimina triloba, following small-scale removal of the invasive shrub, Amur honeysuckle, Lonicera maackii

Abstract

Efforts to reduce the impact of invasive plant species, such as the Amur honeysuckle, Lonicera maackii, often involve the rapid removal of the invasive without any post-removal strategies. This has the potential to stimulate the rapid growth of some native plant species and their herbivores. How this rapid growth may affect plant–insect interactions is not well understood, and unintended consequences may arise. Here we assess how high defoliation rates caused by a native herbivore, Omphalocera munroei, impacted the population of a native understory tree, the common pawpaw, Asimina triloba, following small-scale L. maackii removal. High defoliation rates on A. triloba caused by O. munroei were first detected in two patches of A. triloba that had rapidly expanded following L. maackii removal. Defoliation of A. triloba was estimated throughout a 30-acre site and defoliation, survival, and stem growth were recorded in nine patches (two within the L. maackii removal areas and seven outside) for 6 years. Defoliation peaked during year 2 with near 100% defoliation on > 90% of A. triloba stems and remained higher than reference sites until year 5. Defoliation throughout the site led to > 50% stem mortality, with higher mortality rates observed outside L. maackii removal patches. Stem mortality was high across all age classes, with low recruitment and an unusually high mortality of well-established older plants. These results illustrate the potential for interactions among native species to be destabilized by the rapid colonization and population growth of native species that can occur following removal of an invasive species. Findings from this study highlight the need to consider post-removal restoration strategies following the removal of invasive plant species.