What is a Cedar GladeWhen settlers first came into the mid-south, they noticed places where there were no trees. They called these places "glades” referring to their grassy and tree-less nature..

Cedar Glade plant zones

Cedar glades and barrens are among of the rarest habitat types in the Southeastern United States. Distinctive in appearance, these regions in middle Tennessee (and more rarely in nearby states) are characterized by a mosaic of limestone outcroppings, where the bedrock is exposed or comes very close to the soil surface. Plants in these glades are distinctive. Where rock is closest to the surface, only non-woody plants can grow, but as you move outward and the soil thickens, dense cedar thickets can grow, with hardwood forests in deeper-soiled zones beyond them. The rocky, thin soiled environment of the cedar glade is too harsh for most trees to become established, but red cedar is able to grow in cracks in the bedrock or in random pockets of deeper soil. Consequently, trees in the glade grow widely spaced, in clumps, or in bands on the edges of the glade. This creates a mosaic of light and habitat structure for plants and animals with different preferences. Bedrock based cedar glades, which remain tree-sparse for as long as it takes for soil to form on the bedrock (thousands of years or indefinitely). Where the dense cedar thickets grow around the margins of the glade where the soil is thicker, sun loving species are shaded out. The sunny centers of the glade outcroppings and barrens are home to a wide array of rare and beautiful wildflowers and grasses.

Plants of the glades

While cedars are the primary tree of cedar glades, other tree species include black and bur oak, paper birch, and red maple. These deciduous trees are often stunted or dwarfed because of the scarcity of nutrients and water. Shrubs of the cedar glade include old field juniper and horizontal juniper.

Cedar glades are home to diversewildlife. The rocky terrain is a great place for basking reptiles and nooks and crannies provide an abundance of places for creatures to take cover. The cedars also provide thermal cover, protecting wildlife from cold winter weather, and extreme summer heat.

Approximately 43 acres of these rare cedar glades are present in Stones River National Battlefield in TN. Cedar glades are, as expected, treeless because of very shallow soils. Many of the plants within the glades are endemic, which means they are found exclusively in cedar glades. This plant life is mostly composed of non-woody plants. Plants have adapted to these extreme micro-climates.  

Cedar glades consist of extreme climatic conditions. Winter temperatures in glades are analogous to those of neighboring forest; however, summer temperatures are frequently 10 to 30 degrees higher. Thin glade soils tend to remain waterlogged throughout much of the wet winter and early spring, but dry rapidly during the summer. Then the glade becomes desert like.

Glade plants, like many desert plants, have unique ways of surviving hot, dry summers. Plants that grow in thin soils have very shallow roots and are small. Several glade plants create flowers early in spring and release seeds before the harsh conditions develop. Others plants produce a lot of seeds and a have a life cycle that is very quick. Several glade plants are perennials. They have abundant belowground stems or bulbs that store food. Still others stay alive by having extensive root systems that absorb water from soil under rocks or by storing water in leaves. Other adaptations consist of a plant’s inability to be used as a food source for animals or the manufacture of chemicals that prevent the growth of other plants.

What is an endemic?An endemic is an organism which lives in only a small geographic area or one type of habitat. The cedar glades are unusual in having a large number of endemic species. A few examples will demonstrate the difference between an endemic and non-endemic species.

Many of the glade endemics have adaptations to the harsh conditions of the glades.  They survive on the glades because they can cope with the conditions better than other species.Most glade endemics cannot compete with the plants that grow outside the glades. They survive on the glades because there is less competition.

Rocks of the glades

Cedar glades are underlain by limestone, which dissolves in acid precipitation over time. This cave-filled, “holey” bedrock formation is called Karst topography. Karsts are characterized by porous limestone with deep fissures, sinkholes, underground caves, and streams. Because of the networking of underground water, any stream or river pollution can be devastating to fragile stream and cave life in the entire area. Many of the plants found in cedar glades are called calciphiles (lovers of calcium) because they grow on calcareous (calcium rich) soil. It may not be the case that calciphiles love calcareous soils, but they have adaptated to tolerate high calcium, and low iron and phosphorus levels. Many calciphiles will grow in other soil types but are most competitive in calcareous soil. Plants found in cedar glades are also extremely well adapted to drought.

While cedars are the primary tree of cedar glades, other tree species include black and bur oak, paper birch, and red maple. These deciduous trees are often stunted or dwarfed because of the scarcity of nutrients and water. Shrubs of the cedar glade include old field juniper and horizontal juniper.

Cedar glades are home to diverse wildlife. The rocky terrain is a great place for basking reptiles and nooks and crannies provide an abundance of places for creatures to take cover. The cedars also provide thermal cover, protecting wildlife from cold winter weather, and extreme summer heat.

Our nearby glades in SW Virginia—The Cedars

In southwest Virginia, there are barrens scattered throughout the Virginia Ridge and Valley region, usually occurring on steep, south- to west-facing slopes. Not far from the Tennessee border, Shallow, drought-prone soil on the rocky ground creates an opening in the forest called a limestone glade where specialized plant and animal life survive.

The Cedars region of Lee County contains "flatrock" limestone barrens on gently rolling topography. Soils typically have high pH (> 7.0) and calcium levels. Warm-season prairie grasses characterize the largely herbaceous vegetation and communities in this group are considered state-rare and, in some cases, globally rare. Threats include quarrying,development, grazing, and invasive introduced weeds.

The Cedars Natural Area Preserve is a 50-acre tract at the northern end of the karst, was first purchased as a Nature Conservancy preserve in 1996. It was transferred by the Conservancy to the state in 1997 to become a Natural Area Preserve. Eventually, the Department of Conservation and Recreation which administers the preserve will buy additional land for interpretive trails and public parking.

Running glade clover (Trifolium calcaricum) was found in the limestone glade eight years ago. The only other site where it is known to exist in the world is 200 miles away in Tennessee. Producing creamy-white blossoms with wine-colored veins in May, the running glade clover resembles common white lawn clover, though it is not closely related. It has long, trailing stems, or stolons, which run along the ground and put down additional roots. The endangered herbaceous plant prefers thinly wooded to open areas, and has been located in 24 places over a 5-square-mile area.

The Lee County cave isopod (Lirceus usdagalun), an endangered crustacean resembling a grain of rice with legs, is found in two caves in The Cedars and nowhere else in the world. The tiny, eyeless, unpigmented troglobyte, or cave-dweller, kept plans for a federal prison and a county airport at bay for two years until the projects were moved to other sites.

From a distance, the stand of red cedars, which often serve as a marker for limestone soil, may seem unremarkable. But the same poor, shallow soil in which the cedars thrive, along with a few Virginia pine and chinquapin oak, also supports 16 rare plant species and provides habitat for the loggerhead shrike (Lanium ludovicianus). Once common in Virginia, the shrike is rare to uncommon in the state and declining rapidly. Insects are the shrike's main diet, but it will eat small birds, mammals, and amphibians when insects are scarce. Lacking talons, the shrike is known for sometimes impaling its victim on thorny plants or barbed wire.

Classifying treeless areas

When scientists study these locations, they find more differences than similarities, and have classified these treeless habitats into three categories, all three of which exist in middle Tennessee.

Limestone Cedar Glades Xeric (dry) Limestone Prairies Barrens

Why are there glades in Middle Tennessee?Karst is an area of land that is underlain by rock that dissolves slowly with slightly acid rainwater. 

The glades of the Tennessee Central Basin are the product of half a billion years of geologic history. To understand them, we must go back 460 million years to the middle of the Ordovician Period. At that time, what is now North America sat just south of the equator in a shallow tropical sea. The rock that was deposited under these conditions, called the Stones River Group, is an extremely pure limestone, close to 100% pure calcium carbonate (CaCO3) . Throughout the Paleozoic Era (570-250 million years ago), what is now the eastern edge of North America collided repeatedly with other plates. This caused compressional forces to buckle the earth's surface forming a bulge in middle Tennessee called the Nashville Dome.

With each tectonic collision, the dome would be squeezed and become steeper, and between collisions, it would erode and become flatter. Earthquakes resulted in a major change in the environment, allowing large amounts of silicatious silt to be deposited in the region. The rock that was deposited, was no longer pure limestone, but limestone mixed with large quantities of shale and phosphate. As the Paleozoic Era continued, other kinds of rock were deposited: the black Chattanooga Shale in the late Devonian Period, the cherty Fort Payne Formation in the early Mississippian, and the sandstone of the Pennsylvanian Period.

Differential Erosion: The Carving of the Nashville Basin

Since the end of the Paleozoic Era (250 million years ago) middle Tennessee has generally been above sea level, and the rock deposited during the Paleozoic Era has gradually eroded.

Rocks erode at different rates. Insoluble rocks, such as sandstone, chert, and shale, erode relatively slowly, whereas soluble limestone erodes rapidly. Scientists estimate that the middle Tennessee's Ordovician limestone erodes three times as fast as the rocks of the Fort Payne Formation . Thus as soon as the limestone was exposed, a basin started forming.