Survival, growth, and fecundity of the invasive swallow-worts (Vincetoxicum rossicum and V. nigrum) in New York State

Authors: AVERILL, KRISTINE - Cornell University; DITOMMASO, ANTONIO - Cornell University; MOHLER, CHARLES - Cornell University; Milbrath, Lindsey

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2011
Publication Date: 6/20/2011
Citation: Averill, K.M., Ditommaso, A., Mohler, C.L., Milbrath, L.R. 2011. Survival, growth, and fecundity of the invasive swallow-worts (Vincetoxicum rossicum and V. nigrum) in New York State. Journal of Invasive Plant Science and Management. 4:198-206. DOI: 10.1614/IPSM-D-10-00034.1.

Interpretive Summary: Pale and black swallow-wort are nonnative, perennial milkweed vines that have become increasingly noxious and difficult to manage in the northeastern United States and southeastern Canada. Little is known about the biology of mature plants, so we studied the survival, vegetative reproduction, and seed production of pale and black swallow-wort over three-four years in old field habitats and, for pale swallow-wort only, forest habitats. Yearly survival for both swallow-wort species was around 100% in both old-field and forest habitats. Vegetative reproduction (an increase in number of stems per clump) varied but was highest for black swallow-wort in old fields and lowest for pale swallow-wort in forests. Pale swallow-wort produced more seed per stem than black swallow-wort in old fields. Seed production was generally lowest for pale swallow-wort in forests. Since vegetative expansion and seed production rates were higher in old field habitats, we suggest that management efforts for these species focus control in such higher light environments.

Technical Abstract: Black and pale swallowwort (BSW and PSW, respectively) are perennial, herbaceous vines in the Apocynaceae that are native to Europe. The species are becoming increasingly abundant in the northeastern United States and southeastern Canada and are difficult to manage. However, we know little about the demographic parameters of these species. We determined the survival, annual rate of vegetative growth, and fecundity of mature clumps of these swallow-wort species. We selected four PSW sites (three of which comprised both old field and forest habitats) in central New York State and three BSW old fields in southeastern NY State. BSW is largely restricted to higher light habitats in its introduced range. In each habitat, we followed the growth of 30 to 32 randomly selected clumps of similar size (2 to 5 stems/clump in the initial year) for 3 to 4 years. Yearly survival was 99.6 +/- 0.3% [mean +/- standard error] for PSW and 100 +/- 0% for BSW. In old fields, vegetative expansion varied from -0.01 +/- 0.1 to 4.6 +/- 0.4 stems/clump/yr for BSW and -0.02 +/- 0.2 to 2.1 +/- 0.5 stems/clump/yr for PSW. In forests, PSW growth was lower with vegetative expansion ranging from -0.01 +/- 0.1 to 0.8 +/- 0.2 stems/clump/yr. Fecundity of PSW in 2007 and 2008 [130 +/- 10 viable seeds/stem/yr] was similar to BSW [100 +/- 10 viable seeds/stem/yr]. Fecundity of PSW in forests was generally lower than PSW in old fields, but it varied greatly among sites [0 to 170 viable seeds/stem/yr]. We found that growth and fecundity did not vary with clump size (stems/clump). Since vegetative expansion and fecundity rates were high in old field habitats, but were generally low or nonexistent in forest habitats, we suggest that management of these two invasive vines be focused in higher light environments to reduce overall seed production and its subsequent spread to surrounding areas.