Tuesday, June 26, 2012

Hilary Smith: Invasive Swallow-Wort Vine Expanding Range

What follows is a guest essay by Hilary Smith Director of the  Adirondack Park Invasive Plant Program in Keene Valley.  Swallow-wort is an invasive plant on the move on the periphery of the park. 

The field season is here and the hunt for invasive plants is underway.  Crews, volunteers and concerned citizens have eyes open for new infestations. The best time to detect invasive plants is when they are in flower. Detecting plants early is critical. The sooner an infestation is found, the more likely it is that it can be successfully eliminated.

Swallow-wort vine is in bloom now. It is relatively widespread throughout central and western New York but just starting to make in-roads into the Adirondack region. Time is of the essence to find new locations of this swiftly spreading plant.

Small infestations are known in Elizabethtown along the Boquet River; Willsboro on one property along the shores of Lake Champlain; Malone along the Salmon River; Town of Ohio along Farr Road; Ticonderoga on one private property; and several infestations are just beyond the Park’s western boundary. This is cause for concern.

Ecological impacts are severe, and management is costly. Infestations smother native vegetation, degrade grassland bird habitat, disrupt soil microbial communities and reduce insect diversity. Rapidly expanding populations in Jefferson County are putting at risk federally endangered plants and globally rare habitats.

A member of the milkweed family, swallow-wort produces seeds that can be easily dispersed long distances by wind. Finding new infestations can be tricky since small populations – when elimination is easiest – could go un-noticed. Extra vigilance to search for this plant will be required to hold the line of its spread.

Both black swallow-wort (Cynanchum louiseae) and pale swallow-wort (C. rossicum) are perennial, twining vines native to Europe. Look for oval shaped leaves with pointed tips, 3-4 inches long by 2-3 inches wide that occur in pairs along the stem. Small, five-petaled, star shaped flowers are ¼ inches across and borne in clusters and bloom in June and July. Black swallow-wort has dark purple to almost black flowers with white hairs, and pale swallow-wort has creamy pink to reddish brown flowers.

The fruits are slender tapered pods, 2 to 3 inches long by about ¼ inches wide, turning from green to light brown as they mature. When ripe, the fruits open and release flattened seeds equipped with downy parachutes that aid in wind dispersal. Thick infestations in full sun can produce 2,000 seeds per square meter. Wind dispersal of seed begins in late July to early August and continues throughout late summer and fall.

Swallow-wort tolerates a range of light, moisture and salt conditions. Typical habitats include old fields, hedgerows, brushy areas and the ground layer of woodlands. Both natural and human-caused disturbance including ice-scoured river banks, rocky slopes, transportation corridors, quarries and abandoned agricultural fields provide acceptable habitats.

If you think you see swallow-wort, take note of its location and a photo if possible. Report sightings to Brendan Quirion, Terrestrial Project Coordinator for the Adirondack Park Invasive Plant Program, at 518-576-2082 x 118 or bquirion@tnc.org.

Photos: Above left, Swallow-wort infestations form dense clumps of twining plants. Above right, Swallow-wort fruits are slender tapered pods. Downy seeds can be easily dispersed long distances by wind. Below left, pale swallow-wort has star-shaped, creamy pink to reddish brown, 5-petaled flowers. Black swallow-wort is similar but has dark purple to black flowers. Photos courtesy John M. Randall, The Nature Conservancy, Bugwood.org

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The Adirondack Almanack publishes occasional guest essays from Adirondack residents, visitors, and those with an interest in the Adirondack Park. Submissions should be directed to Almanack editor Melissa Hart at editor@adirondackalmanack.com

One Response

  1. Caitlin says:

    It is great to know what to look for during inventory efforts. Thank you, APIPP!

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