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Prairies, Glades, and Barrens: Rare Habitats for Rare Species

Arkansas Natural Heritage Commission - Wednesday, June 01, 2016

When European explorers and early settlers first came to what is now Arkansas they encountered not an unbroken forest but a diverse patchwork of dense forests, open woodlands, and treeless grasslands. Today, while forested habitats are still relatively common, these naturally open grasslands have all but vanished, causing steep declines in many species of plants and animals that depend on them.

Historical records indicate that there were as many as 2 million acres of naturally open grassland habitat in Arkansas in the early 1800s. These open habitats have been generically referred to as “prairies” in the past. Many were true tallgrass prairies, but others would be more appropriately classified as glades or barrens.

Occurring primarily in the Great Plains and Upper Midwest regions of North America, tallgrass prairies also occur in scattered pockets in areas east and south of this main range. In Arkansas such areas include the Grand Prairie region of eastern Arkansas, the Arkansas Valley prairies east of Fort Smith, and the areas around Harrison, Fayetteville, Rogers, and Siloam Springs in north central and northwest Arkansas that historically supported prairie.

Tallgrass prairies often have rich topsoil and, as the name implies, are dominated by several species of tall grasses, most notably big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), switchgrass (Panicum virgatum), and Indiangrass (Sorghastrum nutans). In addition to these “backbone species”, prairies support hundreds of other species of grasses, sedges, rushes, forbs (wildflowers), and shrubs as well as a rich and varied fauna.

In the Great Plains and Upper Midwest, tallgrass prairies dominated the landscape because rainfall amounts are low enough that drought-tolerant prairie grasses and wildflowers have an advantage over trees, which need more water. In Arkansas, we generally have enough rainfall to support forests so there are other factors responsible for the existence of our prairies. The two main ones are droughty soil conditions (often caused by the presence of a clay or rock layer in the soil near the surface of the ground) that limit the amount of moisture available to plants and the tendency for these areas to burn about once every 2 to 3 years.

In addition to tallgrass prairie, Arkansas had a great deal of blackland prairie at the time of settlement. Blackland prairies are found on limestone formations deposited by the Cretaceous sea that once covered the Gulf Coastal Plain. Confined to the southwest corner of the state, the region consists of several distinct areas of alkaline soil characterized by chalk outcrops, black soil, and cuestas – long, low ridges with a relatively steep face on one side and a long, gentle slope on the other. It is on the steep sides of these cuestas that we find the blackland prairie communities. Typical blackland prairie plants include compass plant (Silphium laciniatum), gamagrass (Tripsacum dactyloides), switchgrass (Panicum virgatum), and purple prairie-clover (Dalea purpurea).


In contrast to prairies, glades typically have much thinner soils and occur where bedrock outcrops or comes very close to the surface of the ground. These are basically rocky “micro-deserts” and are home to true desert plants such as false aloe (Manfreda virginica), rock pink (Phemeranthus calycinus), Arkansas yucca (Yucca arkansana), and eastern prickly-pear cactus (Opuntia humifusa). These habitats generally include a grassland element dominated by shorter annual grasses such as dropseed (Sporobolus spp.) and three-awn grasses (Aristida spp.). Drought-tolerant perennials such as little bluestem and sideoats grama (Bouteloua curtipendula) may occur in areas of thicker soils around rock outcrops. Glades are known for their high number of rare and endemic species.

Barrens in Arkansas, like glades and prairies, are generally the result of extreme soil conditions. Two notable types of barrens occur in Arkansas; saline and sandhill barrens. A saline-soil grassland community, “saline barrens”, occurs where there is thin soil with naturally high levels of sodium and magnesium salts overlying a dense clay layer. These soils are too toxic for most woody plant species and even include areas called “slicks” that are so salty that they lack any plant cover whatsoever. Overall, the vegetation of these saline barrens is most similar to that of glades but they often include small sedge and rush marshes in low, wet depressions.

 

In addition to glades, blackland praire and sandhill barrens are the more likely place we will be working with the Arkansas Game and Fish Commission (AGFC) to remove cedar. The sandhill barrens community occurs on the higher portion of the rolling hills in southwest Arkansas on deep, excessively well-drained sands. This is an open, thinly wooded community characterized by drought-adapted, fire-tolerant herbaceous vegetation with considerable patches of bare sand between plants in some areas. Dominant species include several species of three-awn grass (Aristida spp.), little bluestem (Schizachyrium scoparium), splitbeard bluestem (Andropogon ternarius), slender Indiangrass (Sorghastrum elliottii), and many species of forbs (some very rare).


 




Blackland Prairie remnants


Tallgrass prairie remnants


Glades


Barrens


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