The impacts of a perennial, summer growing invasive species, pale swallowwort (Vincetoxicum rossicum (Kleopow) Barbar.), on spring ephemeral populations.

Background/Question/Methods

Perennial invasive plants have the potential to alter all aspects of their new environments. In the northeastern United States, pale swallowwort (Vincetoxicum rossicum (Kleopow) Barbar.) , a member of the milkweed family that is native to southern Europe, forms dense monocultures during the growing season that are thought to alter native plant populations. However, it is unknown if these summer growing species impact other native plants, such as spring ephemerals, which complete their growing seasons prior to the emergence of pale swallow wort. We conducted our study at two locations in central New York: the Musgrave Research Farm at the Cornell University Agricultural Experimental Station in Aurora, NY and at Robert G. Wehle State Park, located on the shore of Lake Ontario in Henderson, NY. We established 8 paired plots, 8 with no pale swallowwort and 8 with pale swallowwort at Musgrave Farm, but only 8 plots at Wehle since pale swallowwort populations were continuous with no control areas. Plots were sampled in 2011, 2015 and 2017 by counting individual plants of each species within 0.5 x 1-m subplots during late April/early May. Data were analyzed using Analysis of Variance to investigate differences between years and treatments.

Results/Conclusions

At both sites we found a total of 7 spring ephemeral species, with only Erythronium americanum present at both sites. Population sizes varied among years, but only populations of Cardamine concatenata at Musgrave were significantly different among years (F=3.832, P=0.03). Cardamine concatenata at Musgrave was also the only species to have significantly higher populations in plots were there was no swallowwort (F=4.788, P=0.034). There were no significant differences between years or plots at Wehle. It is not surprising that spring ephemeral species were not influenced by a summer growing perennial invasive species since they don’t overlap above ground during their growing seasons. Spring ephemeral populations do vary in space and time, but none of those variations seem to be influenced by the invasive species sharing underground space and resources. It may be that the resource use, aside from space, is so separated in time that no competition occurs between these species.