Do you know where you live?Written by George Ellison
One of the handouts I use during natural history workshops is headed “Southern Blue Ridge Province: Geographic Location and Influences.” It is the best “concise” approximation of the situation that I have been able to devise, as yet. I revise it from year to year, but many of the “facts” therein remain subjective. Here it is:
The Appalachians — created between 300 and 250 million years ago as a result of periods of mountain building brought about when the North American continental plate collided with the plates forming the European and African continents — extend some 2,000 miles from Canada’s Gaspe Peninsula to north Georgia and Alabama. They have been described as “The most elegant mountain range in the world.”
The Southern Appalachians can be defined as the ranges south of the point in northeastern Pennsylvania to which glacial ice sheets extended at the height of the Wisconsin epoch 18,000 years ago. That region consists of four geographic provinces: Piedmont, Blue Ridge, Ridge and Valley, and Plateau. The Blue Ridge is by far the most significant in regard to mountainous terrain.
The Blue Ridge Province of the Southern Appalachians extends from just south of Harrisburg Penn., to the hills of north Georgia just north of Atlanta, encompassing mountainous portions of southwestern Virginia, western North Carolina, east Tennessee, northwest South Carolina, and north Georgia. The Blue Ridge can be divided into northern and southern provinces, with the Southern Blue Ridge Province (SBRP) consisting of the terrain south of Mt. Rogers in southwestern Virginia to Mt. Oglethorpe in north Georgia.
The eastern front or escarpment of the SBRP is clearly defined from Virginia into South Carolina. On its western front the SBRP consists of the Unaka, Great Smoky, Unocoi, and other massive ranges. Connecting the eastern and western fronts are transverse ranges: Blacks, Great Craggies, Great Balsams, Nantahalas, and many others. The Appalachian system as a whole reaches its greatest elevation, largest mass, and most rugged topography in the SBRP where 125 peaks rise 5,000 feet or more, with 49 of them surpassing 6,000 feet. (From Mt. Rogers in Virginia northward to the Gaspe Penninsula only Mt. Washington in New Hampshire exceeds 6,000 feet.)
This topography profoundly influences the region’s average temperature (and thereby its plant and animal life, which exhibit strong northern affinities). The principle of verticality states that for each 1,000 feet gained in elevation the mean temperature decreases about 4 degrees F, equivalent to a change of 250 miles in latitude. (This means that if you travel from the lowest elevations in the SBRP at about 1,000 feet to the higher elevations above 6,000 feet, it’s the equivalent of traveling more than 1,200 miles northward in regard to the habitats you will encounter.)
The SBRP is situated where winds bringing saturated air masses from the Gulf of Mexico and the southern Coastal Plain are cooled and lose much of their content. (Air cools while rising to pass over a mountain range and can hold less moisture than warm air; therefore, heavy condensation occurs where large fronts first encounter massive ranges, as is the instance along the Blue Ridge divide.) The heaviest rainfall in the entire Appalachian region occurs along the GA-NC-SC borders, resulting in annual rainfalls of over 90 inches in many areas. (As much as 145 inches have been recorded with regularity since 1935 along the GA-NC line by the Coweeta Hydrologic Lab located near Otto). Taking this into consideration, some professional observers now refer to the area as a temperate rain forest. The higher elevations of the SBRP can be thought of as a peninsula of northern terrain extending into the southeastern U.S. where typical flora and fauna of northeastern and southeastern North America flourish. The region features approximately 1,500 vascular plants (many of which are considered to be showy wildflowers) and 125 species of trees (in all of Europe there are only about 75 species).
Not all agree on the exact extent of the SBRP. Not all agree on the number of 5,000- and 6,000-foot peaks. Not all agree on the definition for the “principle of verticality.” And so on. Almost nobody agrees on the location of the so-called “Temperate (or Appalachian) Rain Forest.” Here are three excerpts from various sources:
(1) “Temperate Rain Forests” of North America are usually defined by P.B. Alaback’s definition published in 1991 in the “Review of Chilean Natural History”: “Annual precipitation over 1400 mm [55 inches], cool summers stemming from an equable year-round climate with mean annual temperature between 4 and 12 degrees Celsius (39 and 54 degrees F.), and infrequent fire.”
(2) Temperate rain forests in the eastern USA are limited to areas in the southern Appalachian Mountains where orographic precipitation causes weather systems coming from the west and from the Gulf of Mexico to drop more precipitation than in surrounding areas. The largest of these forest blocks are located in western North Carolina, northern Georgia, and far eastern Tennessee, largely in the Pisgah, Nantahala, Chattahoochee National Forests and nearby Gorges State Park. In addition, small areas in the highest elevations of the Great Smoky Mountains also receive substantial rainfall, with Clingmans Dome, for example, collecting about 2000 mm of precipitation per year.
(3) An online description of Jocasse State Park by Stephanie Walker and Dirk Frankenberg reads, in part: ‘Near the southwestern corner of the state, the Blue Ridge escarpment rises over 2,500 feet from the Piedmont to the Highlands Plateau at 3,500 to 4,000 feet above sea level. This difference in elevation has been eroded by rainfall runoff into a half-moon-shaped indentation in the Blue Ridge through which five major rivers make their way towards the sea. These rivers have cut deep gorges into the escarpment, which are known collectively as the Jocassee Gorges after one of the principal streams. Annual rainfalls in the heavily forested Jocassee Gorges region can range upward of 100 inches - the generally accepted definition of a rain forest. In the temperate zone of the United States, this is the only rain forest east of the Olympic peninsula in the Pacific Northwest.’
The so-called “Appalachian Rain Forest” and many other aspects related to the Blue Ridge are starting to assume a mythical status in my mind.