The Smokies is an ancient land-mass. Its plantlife may have evolved uninterruptedly for more than 200 million years. Continental Ice Age glaciation did not reach this far south, and as the Atlantic Ocean has repeatedly inundated most of North America, the Smokies remained an island.
The Evolution of Abundance
Diversity is the biological keynote of the Great Smoky Mountains. Within the national park have been found about 1,500 species of flowering plants, among which are some 100 trees. There are around 2,000 fungi, 50 mammals, 200 birds, and 70 fishes, or more than in the fresh waters of any other national park on our continent. There are about 80 reptiles and amphibians, among which are 22 salamanders, which is probably as many as can be found in any similar-sized area in North America. Present conditions, such as warmth, abundant moisture, and a diversity of environments brought about by the height and dissection of the mountains, are partly responsible for this biotic wealth. But time, the many millions of years this land has been above the sea and south of the ice, has also been an important factor. It has been a span long enough for a great many species of plants and animals to get here and find a niche and for other species to evolve in the region. The story of the arrival and evolution of the present flora and fauna is intimately linked with the dramatic history of our continent.
We can only guess what life existed here during the 130 million years of the Mesozoic era, because no rocks from this period exist in the Smokies. But we can imagine that dinosaurs and primitive birds and mammals roamed the region, as they did other parts of the continent. Toward the close of the Mesozoic, flowering plants evolved and rapidly became the dominant type of vegetation. We can guess that some of these first magnolias, elms, and oaks grew right here in the ancestral Smokies. Newly evolved bees probably helped to pollinate some of the flowering plants.
The story becomes clearer and the life forms become more and more familiar to us during the 65 million years of the Cenozoic, the present era. In the first half of the Cenozoic, subtropical vegetation grew in the southern United States and temperate vegetation grew north to the Arctic. As these plants would indicate by their ability to grow here, this was a time of warm or mild climates throughout the Northern Hemisphere. Land bridges between North America and Eurasia, by way of the Bering Strait and perhaps Greenland, allowed the spread of a remarkably homogeneous flora throughout the then-temperate parts of these two continents. The Great Smokies, with their feet in the South and, as it were, their head climatically in the North, must have had both subtropical and temperate vegetation early in the Cenozoic era.
During the second half of the Cenozoic, a cooling trend set in. The widespread “Arctotertiary” vegetation of the northern latitudes moved southwards through North America and Eurasia. By the end of the Tertiary, which includes all but the past two to three million years of the Cenozoic, the vegetation zones of North America were probably very similar to those of the present. In the Smokies the trees probably ranged from southern types, such as sweetgum, at low elevations through the great mixture of cove forests and possibly to spruce and fir at the highest elevations. After a long period of gradual change in climate, the stage was set for the drastic events of the Pleistocene.
It is hard for us to imagine what an ice age must have been like in our country. Perhaps the only way to imagine it is to visit the Antarctic or one of the great glaciers in Alaska, and to watch giant slabs of ice fall from those towering walls. Then ... mentally transport the scene to the Hudson River valley or to the flatlands of Illinois, while magnifying the thickness of those glaciers several times over. Then imagine the surface of that great ice sheet stretching all the way to northern Canada.
If you had stood near the front of that massive ice sheet, you would have felt the cold air flowing off it. How far south that cold, dense air flowed and to what extent it affected temperatures in the southern states are unanswered questions. But undoubtedly temperatures were lowered throughout North America and perhaps farther south. Some scientists postulate a drop of 5.5 degrees Celsius (10 degrees Fahrenheit) in mean annual temperatures in southern United States. The high pressure that developed over the ice sheet would have pushed storm tracks southward, increasing precipitation in the South.
Such continental ice sheets advanced at least four times as climates cooled, and as many times they retreated during warmer intervals. With each advance and the consequent cooler, wetter climate, there was undoubtedly a southward shift of vegetation belts. In the mountains there would also have been a downward shift of forest types, particularly those of the higher elevations. That is, the higher elevation species would begin to grow down the slope. In sheltered coves temperatures probably did not drop as much as they did higher up or out in the open lowlands, and soils in coves were deeper and more fertile. The coves of the Southern Appalachians thus may have formed a refuge for many temperate species of plants, including some forced southward by the spreading ice. This is a factor in today’s biotic richness or abundance in the Smokies.
On top of the Smokies and other high mountains of the Southern Appalachians, tundra (treeless areas) may have developed as winter climates became too cold and windy even for spruce and fir, which is the situation today on high peaks of the Adirondacks and White Mountains in New England. Accumulations of blocky boulders in higher parts of the Smokies resemble block fields in the northern Appalachians that probably were formed above timberline in late stages of glaciation. From the location of block fields, geologists postulate a treeline in the Smokies somewhere between 900 and 1,500 meters (3,000 and 5,000 feet) elevation during the last glacial period, some 15,000 to 25,000 years ago. If islands of tundra did exist in the Southern Appalachians, it is not likely that tundra mammals would have migrated from the tundra bordering the ice front through the intervening forest to reach such Arctic pastures in the sky. But some birds might have. Water pipits, which today nest in the Arctic and above timberline on our Western mountains, might have bred on these patches of southern tundra. And the few snow buntings which have been seen wintering on Southern Appalachian balds may have been returning to ancestral nesting grounds of the species.