Pale swallow-wort (Cynanchum rossicum) has become a major invader of forested areas of central New York, decreasing the diversity of native species and forming monocultures in susceptible areas. However, the major ecological impacts of this species have not been investigated in a systematic way. We used the methods proposed by the Global Invader Impact Network (GIIN) to investigate the effects of pale swallow-wort in the oak-dominated forests of Wells College, in Aurora, NY. In Summer 2014 we established 10 paired experimental 2 x 1 m plots, where 1 x 1 m was chosen to either remain invaded by pale swallow-wort or to have the swallow-wort removed by cutting at the ground level. Surrounding the invaded area was scattered 10 1x1m control plots that had no swallow-wort present. We evaluated percent cover of swallow-wort and other species, light availability, litter depth, litter biomass, litter decomposition, and soil characteristics (pH, P, K, Ca, Mg, Zn, cation-exchange capacity (CEC), soil moisture) within each of the plots to determine any differences between the invaded and control plots.
There was significantly more swallow-wort in the invaded plots (I, average %cover = 90%) then in the removal plots (R = 0%) and the control plots (C = 1.4%), and correspondingly, much less native plant cover in the invaded plots (I = 0.8%) then the control plots (C = 13.6%). Average light transmittance in the swallow-wort plots was only 52%, while it was almost 100% in the control and removal plots. Soil moisture and litter characteristics weren’t significantly different between the invaded, removed and control plots, but potassium levels were significantly higher in the swallow-wort (I=106 ppm, R= 111 ppm) plots then in the control plots (C=86 ppm), and Zinc levels were significantly higher in the control plots (C=2.5 ppm, R=1.96 ppm, I=1.95 ppm). Finally, CEC was significantly higher in the control plots (C=13.2 meq/100g, R=11.9 meq/100g, I=11.8 meq/100g). Invasion by pale swallow-wort has changed some soil characteristics while allowing others to remain unchanged. Future study will allow us to determine if these effects persist in removal plots and the overall impacts on other biotic aspects of the system, such as soil macroinvertebrate diversity.