Wyoming Basins Ecoregion
Description & Physiography
The Wyoming Basins ecoregion comprises 51,605 square miles (33 million acres) of basin, plain, desert, and "island" mountains in Wyoming, Montana, Idaho, Colorado, and Utah. The area is a veritable ocean of sagebrush interspersed with unusual rock formations, sand dunes, and saltbush communities.
Most of the Wyoming Basins is sagebrush steppe; actually a shrubland mosaic dominated by Wyoming big sagebrush. In places of shallowsoil and on windswept ridges, Wyoming big sagebrush may be replaced by black sagebrush or communities of cushion plants. Gardner saltbush and greasewood are especially common on alkaline soils and basin big sagebrush or silver sagebrush may thrive in more moist locations. The sagebrush landscape of low rolling hills and rugged ravines extends for hundreds of square miles in the Wyoming Basins ecoregion. With the exception of the few riparian areas, much of the sagebrush steppe is devoid of trees offering panoramic vistas as far as the eye can see.
Despite their appearance to a human driving through, the Wyoming Basins are surprisingly diverse. Areas of higher salinity and less precipitation are considered desert shrublands dominated by greasewood, shadscale saltbush, fourwing saltbush or winterfat. These plant communities are typically found where precipitation is less than 10" annually and where the soils contain high concentrations of salts. In some places, the soil surface can be white from accumulated salts. If alkaline areas occur in moist spots or seeps, playas may form with differing amounts of vegetation regulated by soil characteristics.
Running throughout the ecoregion as arteries of life-blood, are riparian corridors. Vegetated by several cottonwood species, willow and alder thickets, ninebark, and occasionally boxelder, these corridors provide abundant food, physical shelter, and life-giving water to dozens of species of wildlife and neotropical migrant birds. The Sweetwater, the North Platte, the Upper Green, the Yampa, and the Bighorn Rivers are major fluvial systems fed by hundreds of smaller streams.
Another outstanding feature of the Wyoming Basins are long, linear ridges of sand dunes, some running 100 miles or more. The dunes may be either actively moving as winds deposit and rearrange the sand, or they may be stabilized by the growth of plants. Ponds frequently occur between the dunes. Plant life on the dunes may be quite specific to these harsh locations and may include blowout grass, Indian ricegrass, sandhill muhly and others.
Weather in the Wyoming Basins is harsh. Although rainfall may reach 16" (40 cm) annually along the base of the mountains, the Basins are mostly in the mountains’ rain shadow. Precipitation in the Basins is typically 6-10" a year. Rainfall less than 10” annually is generally considered desert and the Wyoming Basins ecoregion contains the driest areas of Wyoming. Temperatures range from bitter cold to hot in summer with freezing possible in any month of the year. Although snowfall is less in the Basins than in the mountains, snowfall is very important because snow-melt is slower and more readily absorbed by plants than sudden rainfall.
Plants & Animals
Because most of the ecoregion is gently rolling sagebrush rangeland, the human observer can easily fall into a false sense that this is an empty or biologically dull place. The opposite, however, is true. Fully two thirds of the rare plants endemic to Wyoming are found here. The ecoregion is home to numerous grassland birds (such as Brewer’s sparrow, grasshopper sparrow, and mountain plover), identified as the nation’s most endangered group. The prairie rangelands are also home to prairie dogs whose range has now been reduced to less than 2% of that they Formerly occupied. Prairie dog colonies, in turn, are important to black-footed ferrets (America’s most endangered species), ferruginous hawks, swift fox, mountain plovers and burrowing owls.
Many animals we think of today as forest species (elk, grizzly bears, wolverines) were lowland or prairie species in the 19th century when they were first described by Lewis and Clark. Mountains in the Wyoming Basins today serve as refugia from which these animals might again roam as lowland species if their conservation could be assured.
History & Humans
Early explorers noted the gradual change from grassland on the prairies into the rolling sagebrush shrubland of the Wyoming Basins (Wilcove 1999). Soil and climatic conditions are largely responsible for the shift in habitat. These areas were the open plains grazed by vast bison herds for thousands of years. Large numbers of scavengers (bears, coyotes, vultures, wolves, wolverines) followed the bison herds, cleaning the plains of the millions of dead bison as they died in life’s great circle. Today, the scavenger part of the food chain is largely absent.
In the days before European settlement, the sagebrush shrublands were home to millions of prairie dogs whose burrows and digging activities provided food, shelter, and soil aeration (Whicker & Detling 1988). The prairie dog lands were home to an entire community of animals associated with prairie dog habitat. Ferruginous hawks, mountain plover, swift fox, burrowing owls, and black footed ferrets were frequently found in connection with prairie dog colonies. Today, black- footed ferrets hover near the edge of extinction and the others are declining as prairie dog numbers decline
Despite human conversion of the prairies (in the Midwestern states) to intensive agriculture, the sagebrush shrublands remain surprisingly intact. As a landscape, areas once dominated by sagebrush are still dominated by sagebrush. Cattle and sheep today graze lands which were formerly grazed by bison, although today the bodies of the livestock feed humans, not wild scavengers. Many of the grassland birds of the prairie find refuge today on the sagebrush lands although they are threatened by agriculture elsewhere. This has led to the pronouncement that grassland birds are our most endangered group and places additional importance on their conservation in the Wyoming Basins.