Great Plains Sandhill Grasslands and Shrublands

It is all too easy to take a cursory look at the rolling plains in the eastern one-third of Colorado and think that it is all the same. In the Plains Plants section of this website, we discussed the Plains Shortgrass Prairie ecosystem, which is the primary ecological plant community in this area. In that section, we drove northeast up I-76 toward Nebraska and then turned north on Route 50 to the Pawnee National grasslands.

But if you stay on I-76 and continue toward Fort Morgan, you will encounter a completely different ecosystem, the Sandhill Grasslands and Shrublands plant communities, with their own suite of native plants. The primary reason this change in ecosystem is because of a change in substrate. The soils of the shortgrass prairie are primarily composed of fine sandy loam, but as you approach the eastern boundary of Colorado with Nebraska and Kansas, you begin to encounter dune fields composed primarily of sand.

It is thought that these dune fields developed at the end of the last ice age when streams fed by the glaciers in the Rocky Mountains flowed east and overflowed their banks carrying sand and gravel and creating floodplains of sand. At the same time strong winds blowing from the ice fields piled the sand into dunes, which, over the centuries, gradually stabilized into the present vegetated sand hills.

Sandhill grasslands and shrublands extend far beyond the border of eastern Colorado into Nebraska, southwestern Kansas, western Oklahoma, with significant tracts in northeastern New Mexico and the Texas panhandle. In Colorado the largest tracts of shrublands are found in the South Platte Dune Field (2896 sq. mi.) and the Wray Dune Field (2896 sq. mi.) in northeast corner of the state, and the Black Squirrel Dune Field in east central Colorado (1379 sq. mi.).

The sandhill grasslands and shrublands are identified by the presence of a single indicator plant species, Sand sage (Artemisia filifolia). Sand sage is uniquely adapted to the environment in the sand dune fields in the eastern plains. Firstly it is both fire adapted and also adapted to grazing by bison (more recently, cattle). When disturbed by fire, sand sage is usually top-killed, but then quickly resprouts. Grazing by animals is similar to top-killing by fire, with the same result. When sand sage is occasionally killed completely by fire, research has shown that abundant seedlings sprout after the fire.

Sand sage is very drought resistant, able to survive with as little as 8” of rain annually. In addition this plant is able to grow in nutrient-poor soils because it has the ability to concentrate elements needed for growth in much higher levels than found in its substrate. It has a root system