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Jesup's milk-vetch
The Society works to establish healthy plants in multiple habitats for Astagalus robbinsii var. jesupii along the Connecticut River.
Society works to increase numbers at rare plant location
by Bill Brumback, Conservation Director
Augmentation or introduction of any endangered plant is always tricky, but it is especially difficult in systems with a high degree of natural disturbance. Jesup's milk-vetch (Astragalus robbinsii var. jesupii) is found on open ledges that are scoured by ice and water over the winter and spring each year. This scouring keeps the ledges free of woody vegetation which would shade out the plant, but this open habitat comes with a price: plants and seed of Jesup’s milk-vetch (JMV) can also be drowned or washed away. In such a rugged and v
ariable habitat, the plants seem to reproduce primarily by seed which can be produced in fairly large quantities in good years.
Existing at only three sites in a 16 mile stretch of the Connecticut River, A. robbinsii has reached critically low numbers at one of the sites located on the Vermont side of the river. Moreover this year’s high water levels in late May and June, when the plant was emerging and flowering, has exacerbated the decline. New England Wild Flower Society in collaboration with the VT Natural Heritage Information Project (VTNHIP), the NH Natural Heritage Bureau, and the US Fish and Wildlife Service, is augmenting the Vermont population in the hopes of increasing numbers and breaking what appears to be a three-year cycle of boom and bust for plants and flowering stems.
Between 1999 and 2007 all three sites showed synchronized changes in the number of
flowering stems produced, with marked low numbers occurring every three years. It may be due to maximum flower production occurring at the age of three years in this taxon, or possibly a catastrophic event in the past that removed all adult plants from all three sites, creating a uniform age structure. Since 2007 this cycle has continued at the Vermont site (not at the other two sites). The continued fluctuations in Vermont, in particular a drastic drop in 2009, can also be accounted for by summer floods in 2008 that covered the lower elevations of the ledges. Our plan is to introduce plants during the low years of the cycle, hoping that these plants will survive to produce seed which will increase the numbers in low cycle years, making the cycle less extreme.
Drawing from our experience in augmenting this plant in New Hampshire for the past two years, 125 small plants and seedlings, grown at Garden in the Woods in Framingham, MA, by Jessica Gerke and volunteers from seed collected previously at this NH site, were planted in the rocky thin soil of the ledges by Bill Brumback, Society Conservation Director, and Megan Boyle, 2011 Lovejoy Conservation fellow, Bob Popp (VTNHIP), and Chris Kane (Contract Botanist). A drip irrigation system fed by gravity from water barrels higher up on the bank was erected and the plants are watered daily by a spaghetti tube system on a timer. The water barrels are filled every couple of weeks and the progress of the seedlings is noted.
Although we have had some success introducing plants with this method at another site, any introduction is subject to the vagaries of the weather. Wet weather, such as we are experiencing this June, can cause the seedlings to rot off, and the river could rise up at any time and sweep the seedlings away. Nonetheless, we are hopeful that we can begin breaking the cycle of boom and bust at this site.