Competitiveness of Rosa multiflora Thunb. in varying plant communities and light regimes compared with co-occurring native species

Multiflora rose (Rosa multiflora Thunb.) is a non-native invasive shrub of central lower Michigan that is broadly distributed throughout much of the non-mountainous U.S. Like many non-native invasive species, multiflora rose (MR) colonizes a variety of habitats where it competes with and replaces native plant species. The goal of this research was to compare the light and water use efficiency of MR with co-occurring native woody plants in mature forests with minimal light penetration to the forest floor, young forests with substantial light penetration, and edge or meadow habitats with full sunlight exposure. Photosynthesis rate, transpiration rate, and leaf chlorophyll content were measured for MR and two co-occurring native woody plants. Black cherry and Virginia creeper are native woody plants found to co-occur with MR in every replicate location of all three habitats assessed. MR was significantly more light use efficient than Black cherry at light intensities greater than 750 W/m² and exhibited a much broader light use efficiency advantage over Virginia creeper at light intensities greater than 100 W/m². These results indicate land managers should prioritize surveillance of high value landscapes with high levels of incident light when there is little or no MR infestation, choosing first to remove MR from quality forest habitats with less light because mitigation efforts in these areas are more likely to be successful. Removal or death of overstory plants will increase the risk of encroachment by MR which could also inhibit juvenile recruitment by desired tree and forest floor ephemeral species. Encouraging the growth of overstory plants to shade MR in forests to minimize the amount of light reaching it will reduce MR competitiveness even after MR has been established.