These glades are most highly developed in the area of the Central Basin (Nashville Basin) in Tennessee where they are widespread and display high levels of endemism, which is when a species is confined to a unique geographic location or habitat type.
An extremely fragile ecosystem
As shown in the photos below, much of this fragile ecosystem has been destroyed or severely damaged by humans. Historically, the glades have been viewed as barren wastelands open to activities such as target shooting, drinking, and off-road vehicles. The latter has greatly damaged these fragile ecosystems. Many have been destroyed by urban sprawl, agriculture, and dumping everything from old cars to household appliances.
However, these areas support highly specialized species of plant communities, some of which are found nowhere else in the world.
Soluble limestone rock forms the karst topography of the glades which includes surface sink holes and subterranean water. An underlying cave network is home to many extraordinary cave organisms. Cedar glades are characterized by very thin soil and exposed, rocky patches surrounded by Eastern red cedar trees. In the forested southeastern United States, glade environments vary seasonally. They display standing water in the winter due to poor drainage and hot, dry conditions in summer.
What are cedar glades?
A calcareous glade is an ecological community found in the central eastern United States. Calcareous glades occur where bedrock such as limestone is near or at the surface along with very shallow, sparse soil. Because of the shallow soil and the extreme conditions created by it, trees are often unable to grow in the glades. This results in a habitat that is usually sunny, dry and hot. Calcareous glade vegetation has more in common with a desert habitat than a grassland and is dominated by small spring annuals along with occasional geophyte or succulent perennials.
The use of the words glades and barrens to describe dry, rocky communities in the United States is not applied uniformly and often used interchangeably. Calcareous glade communities can integrate with dry rocky prairies, particularly in sloping habitats. Their unsuitability for agriculture has resulted in the glades lack of development and has allowed them to thrive undisturbed by human development. Cedar in the name comes from the abundance of eastern red cedar trees that grow along the margins of the glades or in cracks in the bedrock where roots gain a foothold.
Rare plant species of Tennessee's cedar glades
Several species of plants grow only in the cedar glades. With such a geographically limited range, they are considered to be very rare. These endemic species include:
Pyne’s Ground Plum (Astragalus bibullatus)
Tennessee Milkvetch (Astragalus tennesseensis)
Leafy Prairie Clover (Dalea foliosa)
Gattinger’s Prairie Clover (Dalea gattingeri)
Glade Larkspur (Delphinium carolinianum ssp. calciphilum)
Tennessee Coneflower (Echinacea tennesseensis)
Glade Cresses (Leavenworthia spp.)
Gattinger’s Lobelia (Lobelia appendiculata var. gattingeri)
False Gromwell (Onosmodium molle)
Nashville Breadroot (Pediomelum subacaule)(pictured directly below)
Glade Phacelia (Phacelia dubia var. interior)
Limestone Fameflower (Talinum calcaricum)
Sunnybell Lilly (Schoenolirion croceum)
Two primary reasons for their survival
These plants develop characteristics that make them particularly well adapted to the specific environment. Many cedar glade plants have traits that help them survive the hot, dry summer. Some are winter annuals, producing seeds that spend the summer in a dormant state and then germinate in autumn. Others produce very long root systems that find their way through bedrock fissures to access water, or they have water storage structures such as fleshy leaves.
Glade plants cannot compete successfully in other environments. Most are very shade intolerant which makes it difficult for them to compete in environments with deeper soil that can support the growth of shade trees and shrubs.
Birds of the glades
Professor Elsie Quarterman
Elsie Quarterman (1910-2014), Professor Emerita of biology at Vanderbilt University and one of the country's first prominent female plant ecologists, was the first woman to serve as an academic department chair at Vanderbilt University. She is best known for her work on the ecology of Tennessee cedar glades. Named in her honor, the Elsie Quarterman Cedar Glade is a 185-acre natural area in Rutherford County, Tennessee that is a recovery site for the Tennessee coneflower.
Professor Quarterman is credited with rediscovering the native Tennessee coneflower (Echinacea tennesseensis) in 1960. The plant is found only in Middle Tennessee cedar glades and was previously thought to be extinct. It became the first plant endemic to Tennessee to be protected by the Endangered Species Act. Because of her efforts to establish more populations within the cedar glades, it was removed from the list in 2011. She also supervised seven doctoral students, including Stewart Ware, a plant ecologist at the College of William and Mary, and Carol and Jerry Baskin, professors of Biology, Ecology and Evolutionary Biology, and Plant Sciences at the University of Kentucky.