Alabama

The unique glades of Bibb County

Bibb County Glades - Photo Courtesy of James AllisonThe extraordinary glades of Bibb County currently
encompass 330 acres of natural landscape, such as hardwood forested bluffs, longleaf pine forests and rocky dolomite glades. Exhibiting an islandlike distribution, the Bibb County glades are famous for eight, striking plant species specialized to grow in these glades and nowhere else. The Nature Conservancy considers its Bibb County Glades Preserve to be the most "biologically diverse piece of land in the state of Alabama." Allison indicates in his research that there are several factors that contributed to this amazing biological diversity.

One factor is the variety of geological formations found in Bibb County. Three geographical regions intersect in Bibb County: the Upper Coastal Plain, the Cumberland Plateau, and the Ridge and Valley. These regions each have a distinct variety of wildlife and plants that intersect as well. A second factor is that the county is mainly rural, meaning that much of the habitat remains intact for wildlife; Allison's third factor is the presence of many outcrops of a very unusual kind of rock. An outcrop is a place where bedrock naturally protrudes through the soil level. Half of the rare plant species in the Bibb County Glades are found predominantly on, or near, open, mostly treeless outcrops, or glades.

Dolomite - Photo Courtesy of Brooks R. DillardDolomite is a sedimentary rock characterized mainly as dark gray and thick bedded, with irregular cavities. It consists mainly of carbonates of calcium and magnesium. Fresh dolomite is often pink, pinkish, white, yellow, brown or gray and can even be black when iron is present in the crystal. When the rock is exposed at the surface it becomes darker as well, due to different types of chemical reactions that can take place. However, dolomite also can be colorless. There are several other types of dolomite found in Alabama and other southeastern states; however, these various different types of dolomite are usually very impure. The usual impurity is silica, which is a crystalline compound occurring abundantly as quartz. This siliceous material, known as chert, forms 40 percent of various different types of dolomite. Chert is a siliceous rock of chalcedonic or opaline silica occurring in limestone. With such impurities being the norm for most dolomite, there is something special about the particular, unusually pure Ketona Dolomite found in the Bibb County glades. This unusually pure, rare dolomite plays an important role in the development of plant life where these particular Ketona rock formations are exposed.

In contrast with other dolomites, Ketona is unusually pure, with only about 2 percent impurities. This fact indicates that Ketona is not affected by or diluted with chert or other impurities. Allison stated that the soil obtained from the weathering of Ketona Dolomite is extraordinarily high in magnesium, which is an element necessary for plant growth. There is a combination of high magnesium levels and shallow, droughty soil where the rock is located. Since the rock is located at or near the surface, conditions are produced in which only adapted plants can survive. Allison's new species are all important members of a community of drought-and magnesium-tolerant plants, plants that were able to evolve in the absence of competition from more species that were common but unable to tolerate a soil laced with magnesium.

Allison suggested that this Bibb County plant community is an ancient one, due to the fact that there are several newly discovered species, including some with primitive features and others whose nearest known locations are hundreds of miles away. The discovery of plant communities prevalent and restricted to a particular region, with multiple undescribed species, usually occurs in remote regions of South America, Africa or Southeast Asia, which makes Allison's discovery of this particular "botanical lost world" all the more amazing.