I just got back from two weeks exploring the forests of the North Carolina mountains. I spent a good amount of time in some of the high elevation forests (near or above 6,000 feet) including Mt. Mitchell, Grandfather Mtn., Mt. Pisgah and Roan Mtn. I also visited some of the lower elevation streams in Linville Gorge and the Wilson Creek watershed (under 2,000 feet). It was interesting to observe the difference in vegetation found in these two habitats. The most obvious was the high elevation conifers of red spruce and fraser fir versus the lower elevation deciduous oak, hickory and magnolias. The shrub and herbaceous layers also reflected this stratification, even within the same genus. For example, the red elderberry and common bluets (a houstonia) were constant companions in the high elevations while the white elderberry and large-leaved houstonia accompanied our low elevation hikes. At least, where I traveled, the companion species almost never overlapped. These species have clearly evolved specific adaptive advantages that enable them to thrive in different niches in a non-competitive manner. This elevation gradient in turn affects the animal species that inhabit the area. For example, winter wrens, northern juncos and golden crowned kinglets, winter visitors in our own Shenandoah National Park (SNP), are year-round breeding residents in these boreal forests. And, of course, it was the chatter of the smaller, yet more vocal red squirrel that filled the coniferous forests, replacing the gray squirrel of the deciduous forests.

I enjoy visiting the forests of other regions. Our own SNP is wonderful, but relatively dry. Excellent for oaks and the associated mammalian residents, including one of the highest densities of black bear in the country, but lacking in the tremendous variety of vegetation that can be found in the wetter habitats of West Virginia and the southern Appalachians.

Nonetheless, our SNP does barely reach high enough to get enough moisture and summer temperature relief to retain a relic boreal habitat. A few red spruce and balsam fir can be found at the 4000’ mountain tops of Stoney Man, Hawksbill and a few others.

Hemlocks, the mainstay of the coniferous forests along the Great Lakes and Canadian border, along with white pine, can only compete this far south in the wet coves where they can keep their feet wet and cool over our hot summers. Relic spruce and fir, gray and white birch, mountain maple, bunchberry, bear-berry, ninebark and Canadian yew, more common in the northern hardwood forests, still fight for survival in disjunct colonies at the highest peaks in the SNP where the elevations approach 4,000 feet.

These spruce and fir forests show up as island colonies along the crest of the Appalachians as one travels south along the Blue Ridge, culminating in a final major stand in the Great Smoky Mountains of North Carolina and Tennessee. But our forests have not always been this way. In fact, the one constant is that, over time, they are in a state of constant flux. The spruce forests of the SNP are known as relic, or disjunct, colonies, all that's left from the solid stand that once covered this region some 10,000 years ago. At the height of the most recent Wisconsin glaciation, some 18,000 years ago, the deciduous trees, such as maples and chestnut, were notably absent from the eastern forests. They had retreated to "refugium," probably in the lower stretches of the Mississippi River in Louisiana. The hemlocks and white pine, being more cold-tolerant, were safely ensconced in refugium in the southern Appalachians. From 10,000 to 4,000 years ago, as this last glaciation released its grip on the North American continent, these deciduous species have slowly increased their range, with the boreal forest transitional line slowly moving both north and up to higher elevations.

As these coniferous forests became isolated islands on high elevation summits, divergent evolution has caused the production of new species. The balsam fir (Abies balsamea) on several peaks in Virginia and West Virginia has evolved into a slightly differing form (Abies intermedia). However, further south, the firs show even greater differences, forming a young endemic (found nowhere else in the world) species, the Fraser fir (Abies fraseri).

The faunal populations also become stranded. If you read Maurice Brook's "The Appalachians, you will learn about the tremendous diversity of salamanders that, stranded on these summits for thousands of generations, have evolved into 25 separate endemic species. These include the Shenandoah, Cheat Mountain, Peaks of Otter, and Cow Pasture salamanders, among others.

Still another effect on our forests resulting from the glaciation impacts the bird populations. As the ice sheet covered the Northern forests, the available Southern forests were split into eastern and western ranges separated by a large, uninhabitable prairie. In this manner, we now have the Eastern yellow-shafted and Western red-shafted flickers; the Eastern myrtle and Western Audubon's warbler. Where they merge in the Midwest today, there is some interbreeding occurring. Are they different species? Depends on whether you are a lumper or a splitter.

To me, the most interesting relics in our forests are the existence of certain extremely large seeded fruits, such as the paw paw, the Kentucky coffee tree and the Osage orange. The seeds are just too large to be evolved for digestion by the existing mammals. And how about those over-sized thorns on hawthorns and locust trees? The thorns are spaced too far apart to prevent todays mammals from eating between the thorns. The generally accepted answer is the former existence of megafauna. It is known that 35 to 40 large North American mammals became extinct about 12 to 10 thousand years ago. These included mastodons, mammoths, giant sloths and beaver, dire wolves, camel, horses, shrub and musk oxen, lion and, of course, the saber tooth tiger. This happened at the same approximate time that the continent was changing from an oceanic climate of mild summers and winters (associated with the Wisconsin glaciation), to a continental climate of hot summers and cold winters (ever live in Chicago?). It is postulated that this stressful environment changed the vegetation, putting the megafauna at a competitive disadvantage with the smaller mammals. It is also acknowledged that at this time, the North American continent was being populated by another predaceous mammal, who had a tremendous competitive edge over all other mammals. Certainly, both factors played roles in the extinction of these species. Perhaps the diseases introduced by Asian man had as significant impact on these large megafauna as they did on the native Indians.

If you have an interest in learning more about our North American forests since the last ice age, I recommend "After the Ice Age" by E.C. Pielou. You will find out that we're currently in only the second glacial age that has occurred in the last billion years. Each glacial age, lasting only about 10 million years, corresponds to periods when the tectonic plates are arranged so that polar cold waters are prevented from mixing with tropical warm waters. You'll also read that we are only 2 million years into this glacial age (the Pleistocene), and have been cooling down over the last 4000 years, fast approaching the next glaciation (would you believe only 5000 years to go?).