High-elevation evergreen forests (dark trees) on Wilburn Ridge and Whitetop Mountain (far background) in Virginia.Consider, for a moment, taking a drive from a low-lying Appalachian valley to the high country of the region's highest peaks. A classic example of such a drive would be taking U.S. Highway 441 from Gatlinburg, TN or Cherokee, NC to the summit of Newfound Gap in the Great Smoky Mountains, or perhaps a trip on the Blue Ridge Parkway in western North Carolina. These incredibly steep (and scenic) drives can easily climb three or four-thousand feet in 20 miles of highway and traverse an incredible array of habitat types, from low-elevation bogs and cove forests to dense, evergreen thickets of spruce-fir forests on the uppermost peaks above 4,500 feet. That 20 miles of driving, in fact, can in many places cover the ecological equivalent of traveling from the southeastern U.S. to Quebec or Newfoundland!
What causes this change from warm, lowland forests to evergreen-dominated woods found more in New England or Canada? The answer lies in climate. As the steep slopes of the Appalachians rise abruptly from their foothills, higher elevations lead to cooler temperatures and, in many cases, higher amounts of precipitation as moist air cools and drops its moisture as rainfall or snow. Some of the East's highest annual precipitation actually occurs in the steep high mountains of extreme western North Carolina for this very reason. While small in size, these high-elevation "islands" have a climate vastly different than their surrounding ridges and thus harbor a unique array of habitats and species, such as the dense spruce-fir forests mentioned in the paragraph above.
The southern Appalachians, however, did not always appear this way. That 20-mile drive through an Appalachian valley, in fact, would have appeared vastly different to the naked eye 10,000-15,000 years ago than it does today. Instead, Appalachian forests at the end of Pleistocene Epoch - the geological period occurring from roughly 2.5 million to 11,000 years before present - were vast, park-like forests dominated by spruce and fir, even at the lowest elevations of Appalachian valleys. Rather than seeing black bears and deer serve as the mountains' larger mammals, massive "megafauna" such as mammoths, mastodons, and musk ox roamed the ridges and valleys. In short, this was a region largely unrecognizable relative to the mountains we see today.
Clues from the past
How do we know all of this? After all, we can't simply hop in a time machine and travel back 15,000 years to view these ecosystems for ourselves. We do, however, have clues that can give us a window into this wildly-varying past. The biggest of these clues come from a small, isolated valley in southwest Virginia. Within this valley - named Saltville for its large salt marshes - lie a series of ancient Appalachian bogs, many of which have been present since long before the end of the Pleistocene. At some point during this period, a huge collection of now-extinct megafauna died and were preserved within the area now covering the valley floor. A sampling of mammoths, mastodons, and even giant bears have been pulled from these bogs and older geological deposits nearby in Tennessee during scientific excavations, providing an incredible look into the fauna of Appalachia's past.
One of Saltville's most fascinating specimens from an evolutionary perspective was a single musk ox that perished in the valley's bogs during this time period over 100 centuries ago. This musk ox skeleton was preserved until the 1960s, when paleontologists unearthed the creature and took samples from inside its cranial cavity, or the open space within its skull. Inside, they found pollen from spruce and fir trees that now occur nowhere near the Saltville valley, instead occupying mountain summits over 4,000 feet higher. This evidence, along with similar findings in sediment samples from the same region, tell us that today's high-elevation forests were much more widespread in the Pleisotcene than they are currently.
More broadly, though, these clues into Appalachia's past serve as examples of one of our most common methods for studying evolutionary patterns and processes. Although evolution has been observed directly both in the field and in the laboratory, many evolutionary studies must rely on evidence such as that found in Saltville to understand a species' past. This reliance on evidence from the present as a window into processes from the past touches on a larger topics called uniformitarianism and is one of our most powerful methods for understanding how evolutionary processes have shaped our world. Here in Appalachia, uniformitarianism has allowed us to make inferences into what our forests and mountains would have looked like thousands of years into the past.
Change to the present
Even with this knowledge, though, a major question still remains: how did these one-vast spruce-fir forests become reduced to small, isolated islands restricted to our highest mountain peaks? The answer again lies in climate. During the Pleistocene, much of North America was covered by vast ice sheets up to 2 miles thick and formed by a much cooler climate than we experience today. Although major glacial activity did not extend into southern Appalachia, the mountains' climate was instead much more like modern-day New England or Canada than it is currently - a fact that allowed cold-adapted species like spruce and fir to persist even in our lower valleys.
As Earth warmed and the Pleistocene ended, however, things began to change. Appalachian valleys were no longer climatically-suitable for these evergreen forests, and their component tree species had nowhere to go...but up! The range of spruce and fir across the mountains gradually retracted until these forests were reduced to their locations today, exiled on the Appalachians' highest peaks. Once again, evidence from the present provides us with a window into this process, including growth data from tree rings and genetic material. This evidence, in fact, also tells us that our mountaintop islands are still retracting, retreating ever higher onto summits that don't have much room left as our climate continues warming. There is concern that with the combined effects of climate change and pollution, these unique forests may not last for long.
...which brings us back to that drive from an Appalachian valley to a high summit. The habitats and organisms our mountainsides harbor are not only varied but everchanging, structured by a menagerie of forces from climate and pollution to competition with other species. The high-elevation forests mentioned here are but one example of these changes, and these forests themselves harbor a staggering number of species that have evolved within our present mountaintop islands and will be detailed in later pieces on this website. _________________________________________________________________
See it for yourself
Clingmans Dome (Great Smoky Mountains NP, NC and TN): Spruce-fir ecosystems
Grandfather Mountain (NC): Spruce-fir ecosystems
Blue Ridge Parkway (Milepost 443 to 423): Roadside spruce-fir
Mount Rogers (VA): Spruce-fir ecosystem - see smartphone guide here
Museum of the Middle Appalachians (Saltville, VA): Pleistocene megafauna __________________________________________________________________
Relevant journal articles
McLaughlin, S.B., D.J. Downing, T.J. Blasing, E.R. Cook, and H.S. Adams. 1987. An analysis of climate and competition as contributors to decline of red spruce in high elevation Appalachian forests of the Eastern United states. Oecologica. 72:487-501.
Potter, K.M., J. Frampton, S.A. Josserand, and C.D. Nelson. 2010. Evolutionary history of two endemic Appalachian conifers revealed using microsatellite markers. Conservation Genetics. 11:1499-1513.
Ray, C.E., B.N. Cooper, and W.S. Benninghoff. 1967. Fossil mammals and pollen in a late Pleistocene deposit at Saltville, Virginia. Journal of Paleontology. 41:608-22.
