Seedbank dynamics of two swallowwort (Vincetoxicum) species

Authors: DITOMMASO, ANTONIO - Cornell University; Milbrath, Lindsey; MORRIS, SCOTT - Cornell University; MOHLER, CHARLES - Cornell University; Biazzo, Jeromy

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2017
Publication Date: 5/10/2017
Citation: Ditommaso, A., Milbrath, L.R., Morris, S.H., Mohler, C.H., Biazzo, J. 2017. Seedbank dynamics of two swallowwort (Vincetoxicum) species. Invasive Plant Science and Management. 10(2):136-142. doi: 10.1017/inp.2017.10.

Interpretive Summary: Pale and black swallow-wort are European viney milkweeds that have become invasive in eastern North America. We evaluated the annual emergence of seedlings and longevity of seeds of pale swallow-wort and black swallow-wort at four different burial depths over four years. Most seedlings emerged within the first year of sowing and no new seedlings emerged after the second year. Black swallow-wort, which has a larger seed, was more successful than pale swallow-wort at emerging from different burial depths. Seedling emergence of pale swallow-wort can be prevented by burying seeds at least 10 cm deep, whereas burial of seeds at greater depths is recommended for black swallow-wort. Because the seedbank for swallow-wort appears to be short-lived, limiting seedling establishment and seed production in affected habitats should be an integral activity of restoration efforts.

Technical Abstract: Pale swallowwort (Vincetoxicum rossicum) and black swallowwort (V. nigrum; Apocynaceae, subfamily Asclepiadoideae) are European viny milkweeds that have become invasive in many habitats in the northeastern United States and southeastern Canada. A multi-year seed bank study was initiated in fall 2011 to assess annual emergence of seedlings and longevity of seeds of pale swallowwort and black swallowwort at four different burial depths (0, 1, 5, and 10 cm) over four years. The experiment was conducted in the field in pots buried with the rim nearly flush with the surrounding soil and filled with a locally collected soil. One hundred swallowwort seeds were sown in seed pans buried in each pot, and emerged seedlings were counted and removed from May through September each year. A subset of seed pans was retrieved annually in October and recovered seeds were counted and tested for viability. The majority of seedling emergence occurred during the first year (92% in 2012), and no new seedlings emerged in the third (2014) or fourth (2015) years. Pale swallowwort had relatively poor emergence at the 0 cm (10%), 5 cm (6%), and 10 cm (0.04%-only one seedling) sowing depths, while at 1 cm 36% of pale swallowwort seeds emerged. The larger seeded black swallowwort was more successful, with two-thirds of all sown seeds emerging at the 1 cm (71%) and 5 cm (62%) depths and 24% emerging at 10 cm. Only 15% of the surface-sown black swallowwort emerged. A large portion of the seeds that germinated at 10 cm, as well as 5 cm for pale swallowwort, died before reaching the soil surface. Of filled seeds that were recovered in 2012 (black swallowwort at the 0 cm depth), 66% were viable. No viable seeds were recovered after the second growing season. Seeds recovered following the third year had become too deteriorated to accurately assess. Key findings are that swallowwort seeds do not appear to survive more than two years in the soil, at least in our experiment, and that black swallowwort can germinate and emerge from soil depths of 10 cm.