i 



62 



directly on Hcwellia aquatilis . habitat alteraticMi by clearijig, 

 draining, filling, and seeding exotics for livestock forage have 

 eiltered much of the bottomland habitat in the Palouse River 

 drainage, and in northern Idaho in general. Adjacent property is 

 heavily grazed year-round and the vernal pools have little 

 remaining native vegetation associated with them. No threats 

 from grazing to this site eire foreseen, althoui^ grazing at hic^ 

 stocking levels would be detrimental. Otherwise, no additicavil 

 significant threats are known. 



D. Inadequacy of existing regulatory nechanisnis: CXirrently, there 

 are no statutes in Montana, Idaho, or Washington which provide 

 state legad protect icm for H. aquatilis . 



E. Other natural or namade factors: "Die narrow ecologiced 

 anplitude and the apparent lack of genetic variation may 

 predispose H. aquatilis to decline or extinction if major 

 environmental perturbatioTS occur (esp. drou^t and habitat 

 alteration) . Also, as suooessional changes occur in the wetland 

 habitats, it is li3cely that populations disappecu: with declines 

 in the associated water tables. 



II. ASSESSMEOT AND RBCa«BNI»nCKS 



12. General assesanent of vigor, trends, and status: Howell ia aquatilis 

 is an annual aquatic species with narrowly defined habitat 

 requirements, and as a result it would be intolerant of major 

 envircaimental alterations. It is known fron 13 sites in the Pacific 

 Northwest (nine in Montana, three in Washington, and one in Idaho) . 

 Population sizes range fron a few to many thousands of individuals, 

 but large yearly fluctuaticxis in population size have been observed. 

 These fluctuations are most li3cely due to annual differences in 

 climatic factors, and to variation in seed germination percentage. 

 Some populaticxis in McMitana are large, and currently appear to be 

 stable. However, lc«g-term suooessicMTal trends in the associated 

 habitats probably result in the occasional disappearance of 

 established populaticxTs. Additionally, habitat alteration is 

 continuing in all extant porticxis of the range, primarily from tuitoer 

 harvesting, development, ard alteraticxi of bottomland habitats. 

 Evidence from recent field surveys in Oregon and California indicates 

 that H. aquatilis has been extirpated from these states. CVing to 

 this curtailment of range, and the ecological and genetic factors 

 summarized above, the ^lecies should continue to be closely monitored. 



13. Reocninendatlons for listing or status change. 



A. Roocmnendatlcn to U.S. Fish and Wildlife Service: On the basis 

 of information obtained during recent field surveys and 

 biologiccil studies, it is reoormended that Howell ia aquatilis be 

 placed in Category 1, as a candidate for listing as a threatened 

 species. Ihe species has been extirpated from a large portion of 

 its previously known global range, and several factors make it 

 susceptible to further serious declines in distributicxi and 

 abundance. These factors include a narrow eoologicad anplitude. 



