Ecology of Cedar Glades. I. Distribution of Glade Flora in Tennessee

"Cedar glades" cover about 5 per cent of the Central Basin of Middle Tennessee at an average elevation of 600 feet. They occupy the flat exposures of Lebanon limestone in an otherwise fertile region. Soil is thin and rocky and moisture conditions are extreme. The soil is saturated much of the time from December to May, the period of greatest precipitation, and becomes increasingly drier through the summer and fall. Open glades and woods dominated by red cedar (Juniperus virginiana) are the most typical communities of the region. Both open glades and glade woods are heterogeneous communities, made up of a few "constants" and a large number of sporadic species, most of which are herbs. There is a close relationship between physiography and vegetation as evidenced by the restriction of glade vegetation to Lebanon limestone in the Central Basin and by the presence of similar glades on Ordovician limestone in Virginia and Missouri. This is probably a matter of available moisture controlled in part by stratigraphy. Ability to survive the spring saturation and fall drought is a factor in determining restriction of species to glade habitats. The plants which are able to survive these conditions meet less competition from mesic species which are unable to invade glade areas. Among species characteristic of glades are endemics, disjuncts and eastern species of western genera.