Growth and reproductive potential of the invasive exotic vine Vincetoxicum rossicum in northern New York State

The alien invasive vine Vincetoxicum rossicum (Kleopow) Barbar. is problematic in the Lower Great Lakes Basin of North America. The lack of effective control strategies exacerbates the need for a better understanding of the growth and reproductive potential of V. rossicum. Thus, a 2-year field experiment was performed in a field site in 2003 and 2004 that was densely colonized by V. rossicum. Mean height of V. rossicum stems was 20% and 45% greater in naturally shaded plots compared with plots receiving full sun in 2003 and 2004, respectively. During the 2-year study, the density of stems 10 cm or taller averaged 134 stems m–2, substantially greater than reported in previous field studies for this species. The high densities of stems and seedlings indicate that this field site may be near or at carrying capacity. Each stem produced, on average, 17 mature follicles with some stems producing as many as 100 follicles. Each follicle yielded an average of 15 seeds, each composed of an average of two viable embryos. A typical V. rossicum stand in this site produced as many as 54 000 seedlings m–2 annually. More flowers (2400 flowers m–2), follicles (2250 follicles m–2), and total seeds (32 000 seeds m–2) were produced in plots receiving intermediate light compared with plants in full sun (1650 flowers m–2, 1600 follicles m–2, and 25 000 seeds m–2) or shaded (1600 flowers m–2, 2000 follicles m–2, and 28 000 seeds m–2) plots. Seeds harvested from follicles in the low light plots were 41% more likely to be dormant than seeds collected from follicles in full sun plots. Seeds collected from plants in full sun plots had the lowest frequency (*36%) of single embryo seeds and the highest frequency (*64%) of multiple embryo seeds. These findings suggest that V. rossicum growth and reproductive output is influenced by light environment. While competitive strategies differ between the light environments, the decrease in viability and germination in shaded sites may not be large enough to affect population growth over multiple generations. The substantially greater growth and reproduction of V. rossicum reported in this study relative to previous research may explain the increasing abundance and range expansion of this species in many Lower Great Lakes regions of Ontario and New York State.