Most people don't think about Tennessee as having grasslands. In fact, many people probably still subscribe to the old adage that a squirrel could have traveled from the Atlantic Ocean to the Mississippi River without ever having touched the ground. The view that eastern North America was mostly a big close-canopied forest prior to European settlement is no longer widely accepted as fact. Many ecologists and botanists argue that the East is littered with various types of grass-dominated communities some covering an area the size of a house or smaller and others that at least historically covered thousands of square miles. All parts of Tennessee presently have or once had grasslands, from the lower elevations of West Tennessee's Coastal Plain to the highest mountain summits along the backbone of the Appalachians. As recognized here, our grasslands fall into four major groups: prairies, barrens, balds, and savannas. The first three are all dominated by grasses or grasslike plants (e.g. sedges) and various herbaceous species. Shrubs and trees are scarce and usually stunted or small in size. Savannas are closely related to grasslands and oftentimes grade into adjacent woodlands and grasslands much like an ecotone. Savannas have more tree canopy coverage than grasslands, generally 10-30%, compared to tree canopy coverage in woodlands which typically is 30-75% or greater. Below, the distinctive characteristics of each system type are described in more detail.
Prairies as recognized here are areas dominated by medium- to tall-statured grasses and herbaceous plants that develop on flat plains or gently undulating landscapes. They typically have deep, fertile soils and historically were almost treeless. Prairies of Tennessee likely were maintained historically by a combination of fire and grazing by megafauna. Some prairie systems however were also partly maintained by the presence of a clay fragipan which restricts the growth of tree roots and oscillates from a winter and spring wet phase to a very dry phase in summer and fall. These are referred to here as Xerohydric Hardpan Prairies. At least one prairie type in Tennessee was probably also maintained in part by the presence of dense clays which were subject to shrink-swell processes, thus restricting tree growth and favoring grasses and herbaceous plants. Prairies were most common in parts of West and Middle Tennessee but prairie-like areas also probably were also found on relativel large plain-like surfaces of the Cumberland Plateau and in wide valleys of the southern Ridge and Valley. The following prairie types are recognized here for Tennessee:
Barrens as recognized here include areas dominated by grasses and herbs that develop on rocky sites where growth of trees is inhibited or slowed due to edaphic conditions such as shallow soils over bedrock, high degree of exposed surface rock, or steep easily erodible slopes. Some sites in the Blue Ridge of North Carolina also fit the definition of Barrens as used here. They are maintained by serpertine soils which are high in magnesium and whose high levels are toxic to many plants. Some authors have used the name Xeric Limestone Prairie for grasslands that occur on sloping rocky sites over limestone or dolomite. I prefer to restrict the term prairie to open, level to gently undulating and deep-soiled communities. Barrens are distinguished from glades by their usually sloping nature, deeper soils, smaller amount of exposed bedrock, and dominance by perennial grasses (vs. annual grasses in glades). Barrens are found in the Western Valley, the Highland Rim, Nashville Basin, Cumberland Plateau, and Ridge and Valley.
Grass balds are high-elevation grasslands found atop some of the highest peaks in the Appalachian Mountains of eastern Tennessee, western North Carolina, and southwestern Virginia, typically over 5,500 feet in elevation. They are dominated by a mix of grasses, sedges, herbaceous species, and shrubs. Surrounding the grass balds are shrub thickets, spruce-fir forests, or northern hardwood forests. Various theories have been posited to explain the origin of grass balds. Theories for their origin have included fire, logging, and grazing. Perhaps the prevailing theory is that they are the remnants of alpine tundra that once extended south during the last Pleistocene ice age. Today the balds are under threat due to shrub encroachment and succession. They are home to many northern species, including several that are significantly disjunct from the Northeast.
Early settlers who crossed parts of the Tennessee landscape described savanna-like scenes--areas with scattered, open-grown oak trees growing above a diverse grassland comprised of a wide variety of native grasses and forbs. Such scenes were described from the Eastern Highland Rim in the area known as The Barrens and they were also described from parts of the Cumberland Plateau. No doubt savannas are probably one of the rarest remaining community types in Tennessee though at one time they may have been one of the more common community types in some areas of the state. Due to the fact that our remaining native grasslands are small in size and are all closely associated with woodlands now, the recognition of savanna remnants has become very challenging. The following savanna types are recognized tentatively with the acknowledgement that these are likely quite different from pre-settlement savannas. They are highlighted however because they are essentially all we have left and studying their modern structure and composition is important to realizing or understanding what was formerly here.