Alabama's Great Butterfly Diversity is Linked to Its Unique Geology and Climate
For the purposes of this atlas, the state is divided into three regions:
[The following is adapted from the Introduction of Butterflies of Alabama by W. Mike Howell and Vitaly Charny]
All Alabama naturalists agree that our state has an extraordinarily rich diversity of animal and plant life. The number of documented butterfly species rivals and surpasses that of most states. Alabama’s great biodiversity is due largely to its wide diversity of geology and moderate to warm climate.
Alabama has high mountainous ridges and deep valleys, foothills of the Appalachians, Black Belt prairie, flat coastal plains, river deltas, lakes, springs, huge cave systems, swamps, Gulf and bay coastlines, and barrier islands. All of this land diversity is drained by numerous river systems, with the mighty Tennessee River coursing through the northern one-fifth of the state. Four-fifths of that portion of the state below the Tennessee River is drained by several major rivers flowing southwestward into Mobile Bay, together forming the Mobile River Basin. A few isolated river basins occur along the southern boundary of the state and empty directly into the Gulf of Mexico, while others empty into the Choctawhatchee, Escambia and Pensacola Bays (Fig. 2).
A distinct line of waterfalls occurs across the state where the harder, more erosion resistant upland Paleozoic-age rocks of the northern half of the State meet the softer, more erosionable Cretaceous-age and younger rocks of the more southerly Coastal Plain (= Southeastern Plains Ecoregion). Rivers and streams crossing this Fall Line are marked by waterfalls and “white water.” The Fall Line extends from immediately west of Florence in the extreme northwest portion of the state down to just above Tuscaloosa and on to Centreville, then courses above Montgomery and eastward to the Alabama-Georgia state line near Auburn and Columbus, GA (Fig. 2). The Fall Line roughly follows the ancient shoreline of the seas that covered this region during the Cretaceous Period (known as the Mississippi Embayment). The Fall Line plays an important role in animal and plant distribution in Alabama. Lowland species often do not cross the Fall Line into the uplands. Conversely, many upland species will not cross the Fall Line into the lowlands of the Coastal Plain (Smith-Vaniz, 1968; Mount, 1975; Mettee et al., 1996; Boschung and Mayden, 2004; Lacefield, 2000).
Recently, Griffith et al. (2001) produced excellent maps outlining the ecoregions in Alabama. Ecoregions are those regions that share certain biotic and abiotic features. They are similar in the type, quality and quantity of environmental resources such as geology, physiography, vegetation, climate, soils, land use, wildlife and hydrology.
The Six Ecoregions of Alabama
Each of these ecoregions is important when beginning a study on Alabama butterflies. Several species of Alabama butterflies are limited to just one of these regions because of some unique feature of that ecoregion. Because the physiographic provinces as described by Lacefield (2000) are so familiar in many Alabamian’s mind, we will try to describe an ecosystem below and give its equivalent to that of Lacefield (2000). Reference to the Level III Ecoregions of Alabama Map (Fig. 2) will serve as an aid to locate these ecoregions as they are discussed.
The Southern Coastal Plain represents the smallest ecoregion in Alabama and is situated along Alabama’s Gulf Coast. It extends from the barrier islands (such as Dauphin Island) eastward to Fort Morgan and the beachfront regions of Gulf Shores to Orange Beach, plus the east, west and north shorelines of Mobile Bay. It includes estuaries, salt marshes, lagoons, bayous, river deltas, and wetlands. Geologically speaking, the delta and coastal areas of Alabama are a recently formed landmass referred to by Lacefield (2000) as “the Delta and Coastal Area” of the Lower Coastal Plain. This area receives huge amounts of sediments from the extensive upstate drainage area of the Mobile River Basin. The area is constantly changing in size and shape due to floods, hurricanes, erosion, and other forces of nature. The Mobile-Tensaw river delta, just north of Mobile Bay, contains extensive swamp lands with hundreds of square miles of cypress trees and hardwoods. This area is mostly an inhospitable region for humans and the environment has been little disturbed by human development. It serves as an important refugium for certain butterfly species. (Fig.1 and 3)
The sugar white sands of Alabama beaches and the sky blue Gulf waters make other parts of this ecoregion a vacationer’s paradise. The coastal areas from Dauphin Island eastward to the beachfront properties around Fort Morgan, Gulf Shores and Orange Beach are presently under intense pressure by condominium developers and others who would alter the natural features of the sand dune community, with its xeric pine flatwoods and salt marsh habitats. This relatively small but ecologically unique region contains some rather distinctive species of butterflies (Twin Spot Skipper, Queen, Great Southern White, Eastern Pygmy Blue, Zebra Longwing, Tropical Checkered Skipper, Dusky Roadside Skipper and Duke’s Skipper) whose continued existence depends upon keeping this region relatively free of residential and commercial development. This area is also an important “stopping-over” and resting area for Monarch butterflies on their annual migration to Mexico.
This ecoregion is basically equivalent to Lacefield’s Coastal Plain physiographic region, which he divides into Upper and Lower Coastal Plains (Lacefield, 2000). The most southern portion of this ecoregion (Lacefield’s Lower Coastal Plain) extends as a narrow band completely crossing Alabama’s southernmost counties. This band encompasses towns such as Dothan, Geneva, Ozark, Luverne, Evergreen, Monroeville, and Grove Hill. The land in this region is relatively flat but includes some areas with low rolling hills. The soils are largely sands, sandy loams, red clays and sandy clays with extensive gravel beds near streams and old stream channels. Native forests are dominated by communities of either longleaf pine/turkey-oak or longleaf pine/scrub-oak. Dominant herbaceous plant species in this area include wiregrasses (Aristida stricta and Sporobolus junceus.) Most of the land has been cleared for food crops such as peanuts, cotton, corn, and soybeans, or devoted to intensive loblolly pine-tree farming. Thus, much of the native vegetation on which butterflies depend has been largely replaced in this region with row crops and pine-tree stands (Mount, 1975). The Palamedes Swallowtail and Delaware Skipper are largely found in this southern portion of the Southeastern Plains ecoregion.
According to Lacefield (2000), the Upper Coastal Plain in Alabama (or Upper Southeastern Plains) lies just north of the Lower Coastal Plain, extending as a band across the state with its northern boundary immediately south of the Fall Line. This area has rolling hills, flat lands, swamps and a unique geological land form known as the Black Belt (which extends, for example, through the towns of Gainesville, Livingston, Demopolis, York, Epps, Selma, Montgomery and Clayton). While soils in the northern portion are largely sands and clays, the Black Belt is underlain by extensive layers of white chalk. At the surface of the ground, chalk layers and organic matter interact and weather over time to produce a rich, black, prairie-type soil known as “chernozem.” This area contained many large, pre-Civil War cotton plantations. Much of the productive surface soils of the Black Belt have been eroded away leaving chalky layers at the surface. Few row crops are produced in the area today and the land is used largely for cattle grazing (Lacefield, 2000). Cedar trees are the dominant trees found in the Black Belt, most commonly growing along fence rows where birds have deposited the seeds of these trees along with their feces. Uncommon butterflies like Mitchell’s Satyr, Phaon Crescent, Tawny Emperor, and Appalachian Brown, are found in this upper portion of the Southeastern Plains Ecoregion mostly in river and swamp bottomlands.
The word Piedmont is a French word that means “foot of the mountains.” This is a roughly triangular region in the east-central portion of Alabama that forms the foot of the Appalachian Mountains (Fig. XX ). The Piedmont is the region where the southernmost edge of the Appalachian Mountains dips below the more recent earth deposits which form the Southeastern Plains (Upper Coastal Plain of Lacefield, 2000). Along its northwestern portion, the Piedmont borders the Ridge and Valley Ecoregion (Valley and Ridge Physiographic Province of Lacefield, 2000). A narrow system of ridges is found along the northeastern portion of the Piedmont east of the Alabama cities of Talladega and Anniston. Cheaha Mountain, the highest point in the state of Alabama (at 2,407 feet) is found in this portion. Elsewhere the Piedmont is dominated by hills.
The Piedmont contains the oldest surface rocks in the state. The outcrops here are metamorphic rocks formed from sedimentary rocks that were molten by tremendous heat and pressure to form slate, mica schist, quartzite, gneiss, phyllite, amphibolite, and marble (Lacefield, 2000; Mettee et al., 1996). The soils are largely clay mixed with rocks. Most of the farms in the Piedmont are rather small and much of the land remains forested. Most of the ridge tops are covered with pines while hardwoods dominate the slopes and bottomlands (Mount, 1975). The area contains numerous small springs and clear upland creeks. No butterfly species appears to be limited to the Piedmont ecoregion of Alabama.
The Ridge and Valley Ecoregion (Valley and Ridge Province of Lacefield, 2000) lies just northwest of the Piedmont and is sandwiched between that province and the Southwestern Appalachians Ecoregion (=Cumberland Plateau of Lacefield, 2000). (Fig. 7). This distinctive physiographic region consists largely of sandstone ridges and limestone and/or shale valleys which are oriented from the northeast to the southwest. The Ridge and Valley ecoregion originates as far north as Pennsylvania and terminates at the Fall Line in Alabama. The region is drained by the Coosa, Cahaba, and portions of the Black Warrior River systems.
The region was formed by folding of the earth’s layers upward to form the ridges and downward to create the valleys (Lacefield, 2000). Some of the ridges rise over 500 feet above the valley floor below. Some of these valleys extend from extreme northeast Alabama all the way to the Fall Line uninterrupted. For example, the Coosa Valley extends 100 miles northeast and southwest (with a maximum width of 20 miles) and crosses Cherokee, Calhoun, St. Clair, Talladega and Shelby counties (Johnston, 1933). The extensive folding of the layers of the earth’s crust to form the ridges exposed expansive seams of sandstone, shale, limestone, and dolomite of Paleozoic age. Alabama’s largest city, Birmingham, lies in one of these valleys (Jones Valley). Here the exposed layers of Red Mountain iron ore and limestone served as the basis of the heavy mining in early Birmingham. Iron ore, limestone, plenty of clean water in this region, and abundant coal seams in the nearby Cumberland Plateau provided the basic raw materials needed for the iron and steel industry for which Birmingham is noted.
Most of the ridges and their steep slopes are relatively inaccessible to the logging industry. So today, these areas consist largely of a varied mixture of native hardwood trees, shrubs and herbs--optimum habitat for butterflies. The rather flat valleys have been largely logged over and contain cities, towns, industries, reservoirs, and farmlands. Limestone springs and coldwater streams are characteristic of this region.
Mount (1975) noted that a puzzling botanical situation was once found in the upper Coosa Valley in Cherokee and Etowah counties. Here was a rather large area of longleaf pine flatwoods with sandy or gravelly soil, much like that of the Lower Coastal Plain flatwoods communities (Harper, 1943). While we have not yet studied butterfly populations in this region, one might find here relict communities of butterflies more characteristic of pine flatwoods in south Alabama. The only documented records of Gorgone Checkerspot are from the Ridge and Valley ecoregion.
The Southwestern Appalachians (=Cumberland Plateau of Lacefield, 2000) is sandwiched between the Ridge and Valley ecoregion to the southeast and the Interior Plateau (= Highland Rim Province of Lacefield, 2000) to the northwest. This is sometimes called the Appalachian Plateau. The rolling terrain rises to 1,800 feet above sea level in northeast Alabama and slopes southwest down to about 500 feet above sea level, where it meets the upper portion of the Southeastern Plains. The City of Tuscaloosa sits nearly at the junction of these two provinces. In the northeast, this province contains some of the most spectacular upland scenery in Alabama. For example, Little River Canyon near Fort Payne is the largest canyon in the eastern United States and has spectacular falls and high, nearly vertical sandstone canyon walls (Fig. 8-12). Other striking regions of natural beauty include Buck’s Pocket State Park near Guntersville. Further to the southwest (near Jasper, Double Springs, Natural Bridge and Haleyville) is the extensive Bankhead National Forest. All of these areas have pristine streams that have carved deeply into the underlying rock strata. The steep canyons provide a cool microclimate that allows some species of butterflies that are more northerly forms to enter the extreme northeastern part of the Southwestern Applachians ecoregion. Butterflies such as the Appalachian Tiger Swallowtail, Dreamy Duskywing, Golden Banded-Skipper, West Virginia White, and Diana Fritillary are found in this area. From Jasper to Tuscaloosa, the coal bed-deposits of the swampy Pennsylvanian Period underlie the surface rocks. This area has been extensively strip-mined for coal for many years, thereby destroying a large part of this beautiful area of our state.
Northwest of the Southwestern Appalachians is a distinctive physiographic region known as the Interior Plateau Ecoregion (= Highland Rim of Lacefield, 2000). This province is often considered to be a part of a larger physiographic region known as the Interior Low Plateaus Province. Rock strata forming the steep cliffs bordering the Tennessee River in this area have been dated as some of the oldest in Alabama (Lacefield, 2000), being Mississippian to Ordovician limestones, cherts, sandstones, siltstones, and shales. The terrain consists of tablelands, hills and plains. The rock strata in this area tilt slightly upward to the north toward the Nashville Dome. The limestone and chert in this area erode to form low hills and rich, red soils.
This region contains Alabama’s Tennessee River valley just northwest of the Southwestern Appalachians Ecoregion. This is an important agricultural part of Alabama where vast quantities of cotton, corn and soybeans are grown. It is also a unique biological region containing a multitude of habitats such as springs, sinks, seeps, caves, and rock shelters. Swamp Metalmark and Bell’s Roadside Skipper are only known from this ecoregion.
Boschung, H. T., Jr., and R. L. Mayden. 2004. Fishes of Alabama. Washington, DC:Smithsonian Books, 736 pp.
Johnston, Jr., Wiliam Drumm. 1933. Ground Water in the Paleozoic Rocks of Northern Alabama. Geological Survey of Alabama, Tuscaloosa, AL, Special Report no. 16: 414 pages.
Lacefield, Jim. 2000. Lost Worlds in Alabama Rocks: A Guide to the State’s Ancient Life and Landscapes. Tuscaloosa, AL: Alabama Geological Society, 123 pp.
Mettee, M. F., Jr., P. E. O’Neil and J. M. Pierson. 1996. Fishes of Alabama and the Mobile Basin. Birmingham, AL: Oxmoor House, Inc., 820 pp.
Mount, R. H. 1975. The Reptiles and Amphibians of Alabama. Auburn, AL: Auburn University Experiment Station, 347 pp.
Smith-Vaniz, W. F. 1968. Freshwater Fishes of Alabama. Auburn, AL: Auburn University Agricultural Experiment Station, 211 pp.