Seed bank dynamics of invasive swallowworts

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

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2015
Publication Date: 1/3/2016
Citation: Ditommaso, A., Milbrath, L.R., Morris, S.H., Mohler, C.L., Biazzo, J. 2016. Seed bank dynamics of invasive swallowworts. Meeting Proceedings. #127.

Interpretive Summary:

Technical Abstract: Pale swallowwort (SW) (Vincetoxicum rossicum) and black swallowwort (V. nigrum; Apocynaceae, subfamily Asclepiadoideae) are European viny milkweeds that have become invasive in many habitats in the northeastern U.S.A. and southeastern Canada. A multi-year seed bank study was initiated in fall 2011 to assess annual emergence and longevity of seed of pale SW and black SW at four different burial depths (0, 1, 5, and 10 cm) over four years. The experiment was conducted 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. Initial seed viability was 97% (black SW) and 95% (pale SW). Pots were checked twice weekly for swallowwort seedling emergence beginning in early May and weekly from July through September. Emerged seedlings were removed. Beginning in October 2012, seed pans were retrieved annually and recovered seed, seed coats and seed coat fragments were counted. Filled seeds (i.e., that appeared to have an embryo) were tested for viability with a 1% solution of tetrazolium chloride. 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. During the 2012 growing season, pale SW had relatively poor emergence at the 0 cm (12%), 5 cm (7%), and 10 cm (0.05%-only one seedling) sowing depths, while at 1 cm 38% of pale SW seeds emerged. The larger seeded black SW was more successful, with two-thirds of all sown seeds emerging at the 1 cm (71%) and 5 cm (66%) depths and 27% emerging at 10 cm. Only 17% of the surface-sown black SW emerged. A large portion of the seeds that germinated in the first year at 5- or 10-cm depths died before reaching the soil surface (pale SW-97%, black SW-48%). Of filled seeds that were recovered in 2012, mainly black SW at the 0 cm depth, 66% were viable. No viable seeds were recovered after the second growing season. Seeds recovered following the third and fourth growing seasons 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 the two swallowwort species can germinate and emerge from soil depths of 10 cm which was not expected.