Oklahoma City lies within the Cross Timbers region, an ancient ecosystem that spans much of central Oklahoma into eastern Kansas and central Texas. The Cross Timbers is a complex mosaic of savanna, glade, and upland deciduous forest dominated by post oak and blackjack oak. Historically, grasslands were interspersed throughout the oak forests, creating a rich transitional area between the eastern forests and the Great Plains.
This ecosystem once supported vast assemblages of wildlife, including great herds of bison and other grazing animals. Even today the remaining Cross Timbers area serves as habitat for significant populations of mammals and birds, which benefit from the area’s rich diversity of flora.
The relatively short, gnarled trees of the Cross Timbers belie its status as ancient woodland. Its appearance is less dramatic than other ancient North American forests. Trees average only 15-40 feet in height and 10 to 20 inches in diameter; however, many existing post oaks and blackjack oaks are 200 to 400 years old. As a result of its diminutive size, the Cross Timbers remains underappreciated as an ecosystem, and most of the forest has been cleared for agriculture. Paradoxically, the modest stature of these trees has served to protect remnant stands of ancient forest, since the forests’ noncommercial timber value limits industrial logging. Important patches remain, especially on steep or rocky terrain.
The Cross Timbers are unique in the world for their assemblage of plants and animals. Existing stands of forest in Oklahoma City have been mapped and identified as Environmentally Sensitive Areas in planokc. Creating wildlife corridors to connect remnant patches will help safeguard the viability of this important ecosystem.
Globally, grasslands are the most altered and endangered of all ecosystems. Temperate grasslands, which include the North American Great Plains, are even more vulnerable, with only about 3% protected from development. Though data on the current range of grasslands exist for most other central U.S. states, no maps or range estimates are available for Oklahoma. Consequently, the extent of remaining prairie in Oklahoma City is unknown.
Historical data indicate that tallgrass prairie once dominated the central portion of Oklahoma from north to south. Reaching heights of nearly 10 feet, the primary species were big bluestem, little bluestem, Indian grass, and switchgrass. Numerous other perennial grasses and forbs were present. In fact, as many as 300 different plant species can grow in just three acres of North American tallgrass prairie, and insect populations can be as high as three million individuals per acre.
The decline of prairie extent in the United States ranges from 80% to 99%, primarily due to plowing and urbanization. However, ranching has preserved tallgrass prairie in some parts of Oklahoma. A major benefit to conservation of prairie is its compatibility with ranching when appropriate management practices are employed.
Humans have impacted the landscape in central Oklahoma for thousands of years. The first prehistoric Native Americans arrived in Oklahoma 10,000 to 20,000 years ago, and their arrival corresponded with significant changes to the fauna of the region, resulting from hunting, gathering, and use of fire to modify ecosystems. Starting in the 1830s, the relocation of Native American tribes from other regions into Oklahoma and the large influx of European settlers in the late 1800s initiated many of the trends we see today.
- Wildfire: In addition to fires started by lightning, fire was deliberately used by Native Americans to maintain open grasslands and savannas, with new regrowth attracting a wide variety of grazing animals. However, beginning with European settlement and fragmentation of the grassland, controlled fire practices dwindled. As a consequence, growth of denser forests and build-up of underbrush lead to hotter, more damaging fires when they eventually occurred. This pattern continues today.
- Herbivory: The rich faunal heritage of the plains included many grazing and browsing animals. This assemblage included bison, elk, mule deer, white-tailed deer, and pronghorn antelope, as well as many small animals.
- Drought: Recurrent droughts tend to limit native vegetation, causing periods in which vegetation abundance and range can decrease.
- Grazing by domestic animals: Less than optimal management practices, where domestic grazing animals feed on grasslands at too high a density, for too long, or during the wrong season, can lead to overgrazing. Overgrazing causes significant changes to the ecological community, as well as erosion. However, grazing can be consistent with positive environmental health in grasslands, when grazing practices mimic those of wild herbivores.
- Decline of keystone species: Keystone species, which are species that play a disproportionately large role in maintaining ecosystem function, included buffalo and prairie dogs on the Great Plains. Loss of keystone species can have major impacts on animal and plant communities and on ecosystem processes, such as groundwater recharge.
- Invasive species: Overgrazing can prime the land for invasion by non-native plant species that are often less palatable to grazing animals. Invasive species are one of the primary causes of biodiversity loss, as non-native species may out-compete native species and disrupt ecological communities.
- Plowing: Plowing causes some of the most dramatic impacts on the landscape. Destruction of the native prairie ecosystem has wide-ranging effects, altering biodiversity, erosion, soil fertility, and groundwater hydrology.
- Urbanization: Together with plowing, urbanization is among the most detrimental forces on native ecosystems. Urbanization leads to changes in ecosystem dynamics, nutrient cycles, groundwater hydrology, and a host of other natural processes. These factors are the primary concern of greenokc