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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

142: Upper Missouri

Major Habitat Type:

temperate upland rivers

Author:

Text modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment. Island Press, Washington, DC, USA.

Countries:

Canada; United States

Boundaries:

This large ecoregion covers all of Montana east of the continental divide, most of northern Wyoming, the northwestern corner of Nebraska, western South Dakota, southwestern North Dakota, and a small portion of extreme southeastern Alberta and southern Saskatchewan. The ecoregion is largely defined by the watershed of the Upper Missouri River.

Drainages flowing into:

The Missouri River is the largest tributary of the Mississippi River. The Missouri originates in the Rocky Mountains at the confluence of the Gallatin, Jefferson and Madison rivers. This ecoregion drains the basins of the Upper Missouri (Robison 1986).

Main rivers or other water bodies:

Other rivers include the Yellowstone in Montana, the Bighorn River in Wyoming, the Little Missouri in all four states, the Grand River, the Moreau River, and the Cheyenne River in South Dakota.

Topography:

Rising over 4000 m at its headwaters in the Rockies, the Missouri River passes through mountainous caverns in the Rockies as well as flatter relief of the Great Plains (Robison 1986).

Climate:

The majority of this ecoregion has an arid grassland ecoclimate characterized by harsh winters, with much of the precipitation falling as snow (Ricketts et al. 1999).

Freshwater habitats:

This ecoregion represents the uppermost drainages of the Mississippi Basin, the largest watershed on the North American continent. The headwaters of this drainage are on the arid eastern slope of the Rocky Mountains. The land gradually slopes downward to the east. The streams change from high gradient mountain streams to slower moving, larger rivers on the plains. A distinctive feature of this ecoregion (along with ecoregions [148] and [143], and [109]) is the presence of isolated wetlands called prairie potholes. These wetlands, which are highly endangered, may harbor endemic species of aquatic invertebrates and plants.

Terrestrial Habitats:

Most of the ecoregion is characterized by grasslands of the Northern Great Plains, with dominant vegetation including grama (Bouteloua spp.), needlegrass (Stipa spp.) and wheatgrass (Agropyron spp.). Western edges of the ecoregion are characterized by temperate coniferous forest dominated by Engleman spruce (Picea englemannii), subalpine fir (Abies lasiocarpa), and Douglas fir (Psuedotsuga menziesii) (Ricketts et al. 1999).

Fish Fauna:

The northern portions of the Upper Missouri ecoregion were subjected to heavy glaciation as recently as 10,000 to 15,000 years ago. Therefore, the landscape of this ecoregion is much younger than areas further south. As a result of this glaciation species diversity of the Upper Missouri is roughly half of the Middle Missouri [143]. The ecoregion is, however, important for its large-river habitat, which supports remarkable species, such as the pallid sturgeon (Scaphirhynchus albus). This large, ancient fish is completely restricted to the main channels of the Mississippi and Missouri rivers from Montana all the way to Louisiana. Quite uncommon, it requires the turbid, sediment-filled waters of large rivers for its habitat. Also present in these streams is the shovelnose sturgeon (Scaphirhynchus platorynchus), the pallid sturgeon’s smaller cousin (Cross et al. 1986). This ecoregion forms the southernmost extent west of the Mississippi for some northern fishes such as the brook stickleback (Culaea inconstans) and the burbot (Lota lota).

Description of endemic fishes:

The Upper Missourihas no known endemic fish, mussel, crayfish, or aquatic herpetofauna species.

Justification for delineation:

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).

References/sources:

Abell, R., Olson, D., et al. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.

Cross, F.B., R.L. Mayden and J.D. Stewart (1986)"Fishes in the western Mississippi drainage" In Hocutt, C.H.a.E.O.W. (Ed.). The zoogeography of North American freshwater fishes. (pp. 363-412) New York, NY: John Wiley & Sons.

Maxwell, J. R., Edwards, C. J., et al. (1995) "A hierarchical framework of aquatic ecological units in North America (Nearctic Zone)". St. Paul, MN. North Central Forest Experiment Station, USDA Forest Service.

Ricketts, Taylor H. Dinerstein Eric Olson David M. Loucks Colby J. (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.

Robison, H. W. (1986)"Zoogeographic implications of the Mississippi River Basin" In Hocutt, C.H.;Wiley, E.O. (Ed.). The zoogeography of North American freshwater fishes. (pp. 267-285) New York, New York, USA: Wiley.

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