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Jesup's milk-vetch Listed: 6/5/1987 Status since listing: Stable Jesup's milk-vetch (Astragalus robbinsii var. jesupii) occurs at three sites along a 15-mile stretch of the Connecticut River in New Hampshire and Vermont. Its habitat is periodically scoured by spring ice flows which remove competing vegetation and deposit fertile silt. The species occupies a small portion of the apparently available and suitable habitat. The annual population size fluctuates dramatically and appears to have been relatively stable since it was listed as an endangered species in 1987. Sumner Falls is the smallest of the three populations. Six plants plants were present in 1987 [5]. It was relatively stable between 1997 and 2005, with six of the nine years supporting between 100 and 154 plants. The exceptions were low counts in 2000 (42), 2002 (81) and 2003 (7). There was no apparent trend. Jesup's milk-vetch stems are difficult to count because they cluster tightly, leading different observers to vary by as much as 21% [2]. Trend analyses of stem counts must therefore be regarded with caution. Inflorescences counts are more reliable (measured observer difference of 6%), but indicate productivity rather than population size [2]. Hartland Ledge is the second largest population. Less than 75 plants were present in 1987 [5]. It was quite variable between 1997 and 2005, reaching a high of 426 in 2004 and a low of 21 in 2000 [1]. Six of the nine years supported between 94 and 226 plants. The population appeared to trend slightly upward, but likely not significantly. Jarvis Hill supports the majority of known plants and is the most dynamic of the populations. About 1,000 plants were present in 1987 [5]. Between 1997 and 2004, it reached a high of 1,798 in 2002 and a low of 234 in 1997 [1]. Annual counts did not cluster around the median of 527. The population trended upward. The U.S. Fish and Wildlife Service 1989 recovery plan set a preliminary recovery goal of establishing or discovering seven new populations of 100-500 plants [3], but no additional populations have been established or discovered since the species was placed on the endangered species list in 1987. Only the Jarvis Hill population meets the preliminary viability goal of maintaining 100 to 500 plants. The New England Wildflower Society has propagated plants from seed many times, but attempts to transplant seedlings or directly sow seeds were unsuccessful [4]. Augmentation protocols are still in development. [1] Cairns, S. and H. Herrmann. 2005. 2005 Astragalus robbinsii var. jesupii (Jesup's milk-vetch) Recovery Activities in New Hampshire. Prepared by the New Hampshire Natural Heritage Bureau for the U.S. Fish and Wildlife Service, Hadley, MA. |
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