The exotic vines Vincetoxicum rossicum (Kleopow) Barbar. and Vincetoxicum nigrum (L.) Moench have become increasingly invasive in low- and high-light habitats in North America, and a biological control program is being developed. These plants experience little damage in North America, so it is unclear how they might respond to introduced herbivores. I conducted an artificial defoliation study on seedlings and mature plants of V. rossicum and V. nigrum grown under different light environments. Under high light, V. nigrum produced more seed and allocated more resources to aboveground tissue (root:shoot ratios < 1), whereas V. rossicum allocated more resources to roots with root:shoot ratios of 1.9 for mature plants and > 3 for seedlings. These differences disappeared with shading. Increasing frequencies of 100% defoliation caused greater reductions in biomass and seed production for both species and plant stages. Shading further reduced biomass and no seed was produced. Defoliation of shaded, but not unshaded, plants caused high mortality. Additional cutting of stem tips increased branching only. Defoliation may be effective against Vincetoxicum plants growing in low-light environments such as forest understories, but appears to be of more limited value in high-light environments unless repeated defoliation occurs.

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 swallowwort species. We selected four PSW sites (three of which comprised both old-field and forest habitats) in central New York and three BSW old fields in southeastern New York. 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−1 in the initial year) for 3 to 4 yr. 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−1 yr−1 for BSW and −0.02 ± 0.2 to 2.1 ± 0.5 stems clump−1 yr−1 for PSW. In forests, PSW growth was lower with vegetative expansion ranging from −0.01 ± 0.1 to 0.8 ± 0.2 stems clump−1 yr−1. Fecundity of PSW in 2007 and 2008 (130 ± 10 viable seeds stem−1 yr−1) was similar to BSW (100 ± 10 viable seeds stem−1 yr−1). 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−1 yr−1). We found that stem growth and fecundity did not vary with clump size (stems per 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.

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