Texas blackland prairies

Category: Grassland, Tundra, and Human Biomes.

Geographic Location: North America.

Summary: The Texas Blackland Prairies are the surviving portions of a once-vast tallgrass prairie and home to a variety of grassland ecosystems.

The Texas Blackland Prairies are a temperate grassland ecoregion running from the Red River in north Texas to San Antonio in south-central Texas, an area of about 20,000 square miles (51,800 square kilometers). The area consists of a main belt of 17,000 square miles (44,030 square kilometers) and two islands of tallgrass prairie grasslands. Tallgrass prairie is an ecoregion dominated by tall grasses, as opposed to the shortgrass prairies characteristic of the western Great Plains, with less than 10 percent tree cover. A similar grass-dominated ecoregion with 10–49 percent tree cover is the savanna.

Tree seedlings and invasive species are regularly eliminated in the prairie by periodic wildfires often set by lightning in the dry season. The fires contribute to the accumulation of nutrient-rich loess soil and organic matter, leading to deep and good fertility.

Tallgrass prairie once covered a much larger portion of North America, including much of the Midwest and the Canadian prairies, but is now perhaps the most endangered large ecosystem in North America. More than 99 percent of the original North American tallgrass prairie has been converted to farmland. Most of the surviving tallgrass prairies owe their survival to rocky hill country that made plowing difficult, as in Kansas; to cattle ranchers who preserved the prairies for grazing, as in Oklahoma; or to nature reserves. In Texas, less than 1 percent of the prairie remains.

Precipitation ranges from 30 to 45 inches (76 to 114 centimeters) a year, mainly in the wet spring, and temperature is mild and temperate, averaging 63–70 degrees F (17–21 degrees C).

The two prairie islands of this biome are the Fayette Prairie and the San Antonio Prairie, which are surrounded by the Piney Woods in the northeast and the east central Texas forests in all other directions. The main belt is divided into four narrow areas aligned north to south: the Eagle Ford Prairie, the White Rock Cuesta, the Taylor Black Prairie, and the Eastern Marginal Prairie. Each of these areas has a characteristic soil type—and that goes a long way toward determining its plant and animal community makeup.

Eagle Ford and Taylor Black have soils that are mainly vertisol clays—soils with a large amount of montmorillonite, an expansive clay that forms deep cracks in dry seasons. These cracks can be big enough to injure grazing livestock that lose their footing. In Texas, vertisol clay soils are commonly called black gumbo and are classified as Ustert vertisols, a category in American soil taxonomy meaning that the cracks are open for at least 90 cumulative days a year.

Vertisol regions are marked by hog wallows, small lakes usually a few feet (meters) across and 1 foot (0.3 meter) or so deep that appear after a rainfall, that is, mud puddles big enough for a pig to roll around in.

The White Rock Cuesta soils are mollisols, similar to vertisols but with less clay content and without the crack-forming characteristics. Mollisols are calcareous and rich in loess, and similar to the soils of the Great Plains and the Argentinian pampas.

The Eastern Marginal Prairie and the San Antonio Prairie are predominantly composed of alfisols, while the Fayette Prairie is composed of both alfisols and vertisols. Alfisols are a soil with abundant aluminum, iron, calcium, magnesium, and potassium, as well as clay-enriched subsoil. Alfisol regions are easily identified by the presence of Mima mounds (named for the Mima Prairie in Washington state), naturally occurring domelike or flattened mounds roughly 1–6 feet (0.3–2 meters) high and 5–150 feet (1.5–46 meters) in diameter, covered in a blanket of tallgrass. There are varying theories as to how Mima mounds are formed, with the leading schools arguing for wind-based origins or the tunneling activities of gophers. It is likely that they can be formed by several factors, either independently or in conjunction.

Vegetation

On Eagle Ford, Taylor Black, the Eastern Marginal, and the prairie islands, the dominant grasses are little bluestem (Schizachyrium scoparium) and indiangrass (Sorghastrum nutans), both of which regrow well after fires. Big bluestem (Andropogon gerardii), though found on the vertisol regions, is dominant only on White Rock Cuesta. Mixed switchgrass (Panicum virgatum) and gamagrass (Tripsacum dactyloides) prairies are found in bottomlands throughout the ecoregion, and near hog wallows in the vertisol uplands.

The Fayette Prairie is home to mixed prairies of little bluestem and brownseed paspalum (Paspalum plicatulum), while in the north, where the soil is acidic, mixes of Silveanus dropseed (Sporobolus silveanus) and mead’s sedge (Carx meadii) are found. The White Rock Cuesta is home to seep muhly (Muhlenbergia reverchonii), hairy grama (Bouteloua hirsuta), and species of Dalea such as prairie clover. The Eastern Marginal is home to the prairie blazing star (Liatris pycnostachya), a tall aster with fluffy purple flowers, and the large-flowered tickseed (Coreopsis grandiflora), a yellow flower resembling a daisy.

Invasive plant species that have threatened the indigenous flora include bastard cabbage (Rapistrum rugosum), giant reed (Arundo donax), Johnson grass (Sorghum halepense), Chinese tallow tree (Triadica sebifera), King Ranch bluestem (Bothriochloa ischaemum), field blindweed (Convolvus arvensis), bermudagrass (Cynodon dactylon), chinaberry tree (Melia azedarach), heavenly bamboo (Nandina domestica), and Chinese privet (Ligustrum sinense).

Steps are being taken to encourage planting of native grasses in the area, which can mitigate some of the effects of climate change. Native prairie plants not only absorb carbon dioxide, but store it in the soil, keeping it “locked up” so it cannot be released back into the atmosphere. The grasses also provide a high-energy biofuel source. Both are incentives for landowners to replant areas with prairie grasses, native wildflowers, and other native plant species.

Fauna

The faunal species that has had the most effect in this biome as an invasive type is the fire ant (Solenopsis invicta Buren), the arrival of which resulted in the decimation of 99 percent of the native ant population and a 66 percent decline in ant-species richness.

Bison and pronghorn antelope were once prominent here, but neither species has lived here in wild herds since the 19th century; bison are raised in small numbers as livestock. Today, there are about 500 species of wildlife, including 327 bird species, 15 of which are threatened. There are seven threatened species of reptiles in the Texas Blacklands Prairies biome.

Other reptile species include the southern prairie lizard (Sceloporus undulatus consobrinus); northern prairie lizard (S. u. garmani); the southern prairie skink (Plestiodon septentrionalis obtusirostris); Texas horned lizard or horny toad (Phrynosoma cornutum), which has horns made of true bone that extend from its cranium and feeds on harvester ants and termites; Louisiana pine snake (Pituophis ruthveni), a nonvenomous constrictor that feeds mainly on the Baird’s pocket gopher (Geomys breviceps), a rodent that may be responsible for the Mima mounds and thus can be found near them; and the timber rattlesnake (Crotalus horridus), which usually hibernates with copperheads (Agkistrodon contortix).

The Arctic bird Smith’s longspur (Calcarius pictus) spends its winters in the blackland prairies. Other common bird species include the yellow warbler (Dendroica petechia), cardinal (Cardinalidae), turkey vulture (Cathartes aura), and hairy woodpecker (Picoides villosus). Mammals in the ecoregion include the coyote (Canis latrans), northern pygmy mouse (Baiomys taylori), fulvous harvest mouse (Reithrodontomys fulvescens), collared peccary (Pecari tajacu), and ringtailed cat (Bassariscus astutus).

Bibliography

Brennan, Leonard Alfred. Texas Quails: Ecology and Management. College Station: Texas A & M University Press, 2006.

Erlickman, Howard J. Camino del Norte: How a Series of Watering Holes, Fords, and Dirt Trails Evolved into Interstate 35. College Station: Texas A&M University Press, 2006.

Gahan, Mary Beth. “Daphne Prairie and Other Texas Grasslands Can Store Carbon and Help Fight Climate Change.” Texas Tribune, 20 Aug. 2020, www.texastribune.org/2020/08/20/daphne-prairie-grasslands-climate-change/. Accessed 30 Aug. 2022.

Peacock, Evan and Timothy Schauwecker. Blackland Prairies of the Gulf Coastal Plain: Nature, Culture, and Sustainability. Birmingham: University of Alabama Press, 2003.

Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks, et al. Terrestrial Ecoregions of North America: A Conservation Assessment. Washington, DC: Island Press, 1999.