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1994 Proceedings
North American Conference on Savannas and Barrens


H. R. DeSelm
Department of Botany
The University of Tennessee
Knoxville, TN 37996-1100

Living in the Edge: 1994 Midwest Oak Savanna Conferences

Explorers and early settlers who came to Tennessee in the eighteenth and early nineteenth centuries found grassy openings in the forests which they generally called barrens. Later writers have referred to the region where small grassy barrens occurred as "the barrens." Modern grassy barrens remnants resemble midwestern tallgrass prairies physiognomically and have many of the same dominant and associated plant taxa.

Grassy barrens occurred in Tennessee in all regions except the Mississippi River Alluvial Plain and the Blue Ridge. In West Tennessee and on the Highland Rim and the Central Basin, they occurred on loess-derived soils or on shallow limestone-derived soils. On the Cumberland Plateau, they occurred on shallow to deep sandstone-derived soils. In the Ridge and Valley most occurred on shallow limestone soils. Most sites, known from the historical record to have been located on gentle topography with deep soils, were destroyed by agricultural practices instituted during the period of settlement ca. 1730-1830. However, annual burning of open range until as late as 1945 allowed some sites to persist and the fire may have fostered spread of barrens dominants. Where not burned, some were lost to forest succession.


The writer's interest in, and search for, Tennessee barrens began in 1954. By 1993, about 120 sites had been found; these sites were periodically examined to build a florisitc list. At 58 sites, sets of 0.5m2 quadrats were placed on a line through the largest opening; quadrats totaled 740. In each quadrat, cover of each vascular species, rock, gravel, bare soil, tree litter, bryophytes, lichens and alga were estimated. Importance values were calculated for each species at each site using relative frequency and relative cover.


The vascular plants of the Tennessee barrens totaled 1095 taxa which was about 39 percent of the known Tennessee flora. Nine percent of the taxa were introduced; they occupied niches similar to native plants, and were otherwise indistinguishable. Most taxa were intraneous, but extraneous northern, southern, and western taxa totaled 17 percent of the flora. Barrens endemics were very rare, but some cedar glade endemics entered the flora, and more than five dozen Tennessee rare plants occurred. Richness of individual sites varied with size, number of my visits, presence of a forested border, length and intensity of grazing history and mowing-bush hogging frequency. Stock grazing history was certain but generally little is known of kinds of stock, of their numbers, or of the decades of this land use. Deer use was common.

Dominants of this vegetation were a number of grasses characteristic of the tallgrass prairie. Xeric sites were dominated by Schizachyrium, Bouteloua, and perennial Sporobolus species. Mesic sites were dominated by Andropogon gerardii and Sorghastrum. On wet mesic sites, large perennial Panicum spp. were dominant. On hydric sites mixed sedge communities with several grasses occurred; Spartina was rare, and Tripsacum was only occasional. Hundreds of other graminoids, forbs and woody plants occurred on the moisture series. If not bushhogged or burned, barrens sites may succeed to forest. The most xeric sites may be held open by episodic drought. Shallow soils and winter-wet/summer-dry pan soils slow succession. Barrens bordering high energy streams may be held open by flooding..


The origin of barrens and arrival of extraneous taxa is problematic. The species mix and paleo record do not argue for a single emigration period of expansions period. Emigration may have been over a long geologic period (Miocene-Pleistocene). Climatic forces that might have caused expansion have been followed by cool periods when barren areas would have contracted. Another agency such as fire was probably necessary to maintain the grass-land types. Elimination of forest canopy in 53-56 years was projected in a study of annual and periodic surface fires on an oak forest in Middle Tennessee.

We are in the "locate and inventory" stage of barrens work in Tennessee. The paucity of rectangular land survey records has slowed the search procedure. The absence of local graze/browse intensity information makes interpretation of floristic details per site difficult. Long-term study of sires seems essential but few are located on public lands and indeed repeated inventorying may degrade the biotic features. Studies of species interactions, species life histories, island biogeography, demographic fluctuations and evolution of races of barrens species have been carried out in other grasslands but rarely locally. Other questions remain as to the survival of our remnants in the face of climatic change, weed invasions, wildflower thieves, new insect and disease pests, woody succession, and air pollution effects. Will the barrens survive these current and future threats?


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