Carex hallii Olney
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Carex parryana var. hallii, Carex parryana ssp. hallii, Carex parryana
Basis for Listing
Carex hallii is a species of wet or moist saline prairies in western Minnesota. Beyond Minnesota it is found in similar habitats in the northern Great Plains, but it does not appear to be particularly common anywhere. Its habitat in Minnesota was abundant at one time, extending through the western tier of counties from Canada to Iowa. More than 90% of that habitat is now gone, converted to crop production by the early settlers. Surviving habitat fragments are often too small to have retained the ecosystem processes that originally maintained them, such as fire or bison grazing, and now require intensive management to maintain their biotic integrity. Carex hallii was originally listed as a threatened species in Minnesota in 1984, but was reclassified as special concern in 1996.
Carex hallii is a perennial sedge that typically grows 25-40 cm (9.8-15.7 in.) tall, occasionally reaching a maximum height of about 90 cm (3 ft.). The stems arise singly or as a few together from a long, horizontal rhizome that can exceed 15 cm (6 in.) in length. The leaf blades can reach 3.5 mm (0.14 in.) in width. The inflorescence consists of 2-6 stiff, cylindrical or short-oblong spikes. The terminal spike is 1-3.5 cm (0.4-1.4 in.) long with either male flowers near the top and female flowers below or unisexual flowers. The lateral spikes are usually somewhat smaller and entirely female. The perigynia (the membranous coverings of the seeds) are hairless or sometimes with short, stiff hairs at the apex. They are broadly ellipsoidal to obovoid, 1.9-2.6 mm (0.07-0.10 in.) long, and 1.3-1.8 mm (0.05-0.07 in.) wide. Carex hallii is superficially similar in appearance to C. scirpoidea (northern single-spike sedge), and the two species sometimes occur together. They both have stiff, nearly leafless culms and dense cylindrical spikes, but C. scirpoidea usually has only one spike per stem and has densely hairy perigynia.
The best habitats of C. hallii are sometimes called saline prairies. Although these habitats do not exhibit the extreme salinity sometimes seen in arid regions of the western United States, precipitated salts do give the surface of the soil a whitish cast, at least under certain circumstances. The conditions that result in salinity are usually present in certain small wetland basins or in narrow, sinuous swales. Although the degree of salinity in the soil is not really known, the effects can be seen on the composition of the vegetation. The plant species in these habitats tend to be shorter in stature than species in surrounding vegetation, and they are more widely spaced. Typical associated species include Hordeum jubatum (foxtail barley), Distichlis spicata (saltgrass), and C. praegracilis (clustered field sedge). Secondary habitats of C. hallii include mesic prairies and brush prairies.
Biology / Life History
Carex hallii is a perennial graminoid that produces wind-pollinated flowers on a yearly basis. The seeds are probably dispersed short distances by wind, gravity, and water, and long-distances by a variety of animals. However, in stable habitats, most reproduction is probably clonal. Stems are produced from subterranean rhizomes that are capable of uni-directional growth of at least a few centimeters a year. The response of C. hallii to environmental conditions has not been studied, but based on the nature of the habitat where it is found, a few assumptions would be reasonable. It is likely that C. hallii is adapted to dormant season fire as well as short-term spring flooding and cyclical, multi-year drought.
Conservation / Management
Carex hallii has been found in prairies that have a history of cattle grazing and/or cutting of native hay. It is not known how C. hallii responds to these activities other than that it has survived in some cases. However, it would be unwise to assume that these activities would not be harmful. There is ample evidence that even light grazing and mowing will cause the loss of certain native species and increase the number and abundance of non-native species. It would also be unwise to assume that grazing cattle on isolated prairie fragments mimics the effects of bison grazing on the original unfragmented prairie. Carefully timed prescribed fire could be a useful management tool to control invasion of woody plants, although portions of most saline prairie will probably have too little fuel to carry a fire in most years.
Conservation Efforts in Minnesota
Carex hallii is known to occur in several prairies that are being managed for the perpetuation of the native vegetation. The management usually involves prescribed fire, which seems appropriate. However, the effects of this management on C. hallii are not being monitored.
Minnesota Department of Natural Resources. 2009. Map of Minnesota's remaining native prairie 100 years after the public land survey.
Murray, D. F. 2002. Carex sect. Racemosae. Pages 401-411 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.