INVENTORY, DESCRIPTION AND MANAGEMENT OF SANDSTONE
GLADES IN WESTERN LOUISIANA
Barbara R. MacRoberts
A number of recent papers on open forest communities--prairies, barrens, bogs, rock-outcrop communities--reinforce the fact that very little is known about the plant communities of the Western Gulf Coastal Plain. For example, Quarterman et al. (1993) show the general distribution of limestone, sandstone, and granite outcrops in the southeastern United States but record none for Louisiana or Texas. Again, in a review paper by DeSelm and Murdock (1993) on grass dominated communities of the southeastern United States, we find only part of one sentence devoted to Louisiana calcareous prairies. These two sources typify knowledge about plant communities in the west gulf coastal plain. Except for major community types which are extensions of eastern forest types, western Louisiana and eastern Texas remain terra incognita, some of the poorest known and described sections of the North American continent.
However, instead of biological uniformity and poverty, the west gulf coastal plain is rich in plant species and communities. Some of the plant communities found in this area are glades, barrens, bogs, outcrops, swamps, prairies, savannas, pine and hardwood forests. Many of these communities remain to be studied. Over the past few years, we have begun to describe the communities on the Kisatchie National Forest located in the center of the West Gulf Coastal Plain.
Our purpose in this paper is to make known some of the rich variety of plant communities that characterize our area and to report on some of the work that is being done on them. Specifically, we describe what are locally known as sandstone glades and sandstone outcrops (MacRoberts and MacRoberts 1992, 1993a, 1993b, 1993c). Both are inclusion communities embedded in the pine forests of the southeast.
Between 1991 and 1993, we made biweekly visits to 3 glades (1.2 to 1.9 ha in size) and 3 outcrops (0.4 to 1.2 ha in size) to collect specimens of all vascular species, examine transects, collect soil information, and study tree survival and growth. In addition, using aerial photographs, we located, mapped, and surveyed many additional glades and outcrops.
Sandstone glades are open, often mesa like, with acidic nutrient poor soils. They are strewn with boulders and scattered with old, slow growing, stunted pines and oaks. They are not rich in vascular species; the three glades had between 43 and 69 taxa. Dominant families in glades were grasses and composites accounting for a third of the flora. No rare species were discovered in these habitats.
Sandstone outcrops consists of a rock pavement or ledge without boulders. They are upslope from open calcareous prairie-like habitat, and support old slow growing pines and oaks. Outcrops are much richer in species than glades. Three had between 82 and 110 species. Calcifiles predominate with peas, grasses, and composites accounting for about 40% of the species. Several locally rare species such as Talinum parviflorum, Schoenolerion wrightii, Selaginella riddellii, and Carex meadii occur on outcrops.
Both glades and outcrops are rich in lichens and mosses; unfortunately no one has undertaken to study this interesting component of the flora.
Outcrops appear to resemble most closely the cedar glade type of community in Tennessee and Kentucky while sandstone glades appear to be peculiar to Louisiana.
Special management techniques and procedures are being implemented on the Kisatchie National Forest to maintain and enhance sandstone glades and outcrops. Glades and outcrops are routinely included in prescribed burns to control hardwood invasion and to stimulate herbaceous vegetation growth. Glades and outcrops are signed and/or fenced; and vehicular use and grazing are discouraged in these areas. An inventory of glades and outcrops on the Forest is ongoing with the location and pertinent information specific to each site entered into the Forest Geographic Information System (GIS). GIS data and information pertaining to glades and outcrops are readily available to Forest managers for their use in project planning.
DeSelm, H. R. and N. Murdock. 1993. Grass-dominated communities. In: W. H. Martin, S. G. Boyce, and A. C. Echternacht. eds. Biodiversity of the Southeastern United States: ä Upland Terrestrial Communities. John Wiley, N.Y.
MacRoberts, B. R. and M. H. MacRoberts. 1993a. Floristics of two Louisiana sandstone glades. Phytologia 74:431-437.
MacRoberts, M. H. and B. R. MacRoberts. 1992. Floristics of a sandstone glade in western Louisiana. Phytologia 72:130-138.
Quarterman, E., M. P. Burbanck and D. J. Shure. 1993. Rock outcrop communities: Limestone, sandstone, and granite. In: W. H. Martin, S. G. Boyce, and A. C. Echternacht, eds. Biodiversity of the Southeastern United States: Upland Terrestrial Communities. John Wiley, N.Y.