Assessing the effects of invasive Ligustrum sinense and Lonicera japonica on rare and federally threatened Scutellaria montana

Few studies have directly evaluated the competitive interactions between invasive and co-occurring rare plants. Federally threatened Scutellaria montana Chapm. (large -flowered skullcap) is a rare herbaceous perennial endemic to southeastern Tennessee and northwestern Georgia. The forest understory habitat in which S. montana typically occurs often also contains invasive Ligustrum sinense (Chinese privet) and Lonicera japonica (Japanese honeysuckle), and these and other invasive plant species have been recognized as a potential threat to its conservation. To directly investigate the effects of invasive L. sinense and L. japonica on S. montana, a two-year field-based removal experiment was conducted in an S. montana occurrence in Chattanooga, TN. An interacting herbivory exclosure treatment was included to help isolate the effects of competition from non-insect herbivory, another possible pressure negatively influencing S. montana, and to isolate the effects of competition from apparent competition. I hypothesized that interspecific competition with L. sinense and L. japonica would negatively affect S. montana by reducing its organismal-level growth and fecundity. Additionally, I hypothesized that herbivory would negatively influence S. montana individuals due to the direct removal of aboveground biomass and that negative impacts would be exacerbated by concurrent competition with invasive species. My results suggest that invasive L. sinense and L. japonica do not exert any competitive affect on the organismal-level performance of S. montana. Instead, the presence of these invasive species favors the growth of S. montana individuals by protecting them from herbivores. However, the demonstrated ability of both L. sinense and L. japonica to form monocultures in the forest understory remains a concern given the potential populationlevel impacts of such density on germination and recruitment of co-occurring species. Related research has suggested that other invasive species exhibiting no competitive effect on adults of rare species can suppress their germination and recruitment of juveniles. I suggest that future research include investigations of the influence of L. sinense and L. japonica on these processes in S. montana