With over 120 images, this text provides an overview of the landscape of this region, including the major changes that have taken place over the past 300 million years; describes the different types of forests and other plant communities currently present in Central Appalachia; and examines living systems ranging from microorganisms and fungi to birds and mammals. Through a consideration of the history of humans in the region, beginning with the arrival of the first Native Americans, A Natural History of the Central Appalachians also discusses the past, present, and future influences of human activity upon this geographic area.
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About the Author
Steve Stephenson has lived, worked, and carried out research throughout the Central Appalachian region for much of his career. He is a Research Professor in the Department of Biological Sciences at the University of Arkansas and the author of Myxomycetes: A Handbook of Slime Molds and The Kingdom Fungi: The Biology of Mushrooms, Molds, and Lichens and a coauthor of Macrofungi Associated with Oaks of Eastern North America.
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A Natural History of the Central Appalachians
By Steven L. Stephenson
West Virginia University PressCopyright © 2013 West Virginia University Press
All rights reserved.
INTRODUCTION TO THE CENTRAL APPALACHIANS
THE REGION DEFINED HEREIN as the Central Appalachians consists of a system of linear ridges with intervening valleys, deeply dissected plateaus, and other landforms that produce a generally rugged terrain in western and southwestern Virginia, eastern and central West Virginia, western Maryland, and a portion of south central and southwestern Pennsylvania (fig. 1). It encompasses portions of the Blue Ridge, Ridge and Valley, and Appalachian Plateau physiographic provinces as delimited by Fenneman (1938). For the purposes of this book, the southern limit of the Central Appalachians is considered to correspond to the state boundary between Virginia and North Carolina (which occurs at 36° 30' N). The northern limit in south central and southwestern Pennsylvania is not as clearly defined but is represented by the approximate southernmost boundary of the area of eastern North America covered by ice during the last glaciation, something that will be considered in more detail later in this chapter. The eastern limit coincides with the eastern edge of the Blue Ridge Mountains, the western limit with a line drawn from the valley of the Monongahela River in north central West Virginia and southwestern Pennsylvania (at approximately 79° 51' W) to the point in southern West Virginia where the boundaries of West Virginia, Kentucky, and Virginia intersect (about 37° 32' N, 81° 58' W). Although this line was arbitrarily drawn simply to delimit the general extent of the region actually being considered in this book, most areas to the east of the line occur at elevations greater than two thousand feet.
The Central Appalachians are only one part of the Appalachian system, which extends more than fifteen hundred miles from central Alabama to the island of Newfoundland in Canada. At its widest point, the entire system (including mountain ridges along with associated hills, plateaus, and other elevated portions of the landscape) is as much as three hundred miles across. Although not considered among the world's great mountain ranges, the Appalachians are the single most important topographic feature in all of eastern North America.
The topography, climate, and poor soils limit agriculture throughout much of the Central Appalachians. As a result, forests still exist over most of the region. These forests range from mixed mesophytic and Appalachian oak on low- to mid-elevation sites to northern hardwood and red spruce at higher elevations. The forest cover is not complete, and there are a number of other vegetation types of more limited distribution. Among these are vegetation types associated with mountain bogs, grass balds, shrub balds, and shale barrens. This wide range of botanical diversity is accompanied by a corresponding high diversity in the overall biota.
GEOLOGIC HISTORY Shortly after I moved to West Virginia after accepting a position as an assistant professor of biology at what was then Fairmont State College, Dale Naegele, a geologist at the college, invited me to go on a fossil collecting trip to an area near the Fairfax Stone. As most West Virginians know, the Fairfax Stone is one of the most significant historical landmarks in the state. Located near Blackwater Falls State Park in Tucker County, the stone once marked the western boundary of land granted to Lord Fairfax by the king of England in the eighteenth century. Almost two centuries later, in 1910, this stone was of major importance in establishing the final state boundary between West Virginia and Maryland. Our trip to the area did not involve the stone marker: we were there to collect plant fossils from exposed layers of rocks that dated back about 300 million years (fig. 2). The plants represented by these fossils lived at a time when the Central Appalachian region was very different from what it is today. Instead of being mountainous, the landscape 300 million years ago was relatively flat, and most areas were not much above sea level. Evidence for this is the presence of thin layers of limestone (rocks that consist mostly of lime, more properly known as calcium carbonate) derived from marine sediments occasionally found interspaced among the layers that contain the fossil plants, which clearly have a non-marine origin. The predominant vegetation type, based on the evidence provided by the fossils themselves, was swamplike. Trees were present, but they were primitive forms quite unlike anything currently found in Central Appalachian forests. The fossils we collected that day were in a layer of shale (a type of rock formed largely from clay-sized mineral particles) just above what is usually referred to as a coal seam. The exact origin of coal was a disputed subject until the eighteenth century. Coal is essentially organic material (mostly from plants) that has been chemically and physically altered to the extent that its botanical origin is no longer readily apparent. As will be discussed later in this book, these coal seams have had a profound impact on parts of the Central Appalachians.
All the rocks associated with the plant fossils were sedimentary rocks, rocks formed from the mineral materials (or sediments) that settle and accumulate on the bottom of a body of water. The sediments that ultimately accounted for the formation of coal were produced by a range of mountains in what is now eastern Virginia. Vast amounts of sediments must have been involved, since there are places where sequences of rock layers containing coal seams are found over a vertical distance of more than one thousand feet, and the period of the earth's history during which the coal seams were formed lasted for many millions of years. The most commonly encountered type of sedimentary rock in the Central Appalachians is sandstone, which forms from sand-sized mineral particles. Two other fundamentally different types of rocks are metamorphic rocks and igneous rocks. The latter are formed directly from the mineral material that makes up the deeper, molten layers of the earth's crust, while metamorphic rocks are formed from sedimentary rocks or igneous rocks whose basic structure is altered after being subjected to intense heat and pressure.
Just what does the age of the fossils (approximately 300 million years) collected from the locality near Fairfax Stone mean in the context of the history of the earth? First of all, evidence from radiometric dating indicates that the earth itself is about 4.55 billion years old. Geologists and other scientists have plotted the time that has passed since this event on a schema known as the geologic time scale, which they have divided into units delimited by major geological and paleontological events. The units of the geologic time scale most useful in a discussion of the history of the Central Appalachians are the geologic eras and the periods into which they are divided (table 1). For example, the Paleozoic era, which extended from 542 to about 251 million years ago, is made up of six periods, of which the Cambrian is the oldest and the Permian the most recent. The fossils that we collected near the Fairfax Stone (as well as the underlying coal seam) dated back to the very end of the Carboniferous period. North American geologists have usually further divided the Carboniferous into two subdivisions — the Mississippian (359 to 318 million years ago) and the Pennsylvanian (318 to 299 million years ago).
As a result of shifting tectonic plates (a process known as plate tectonics), the land surface of the earth has continually reshaped itself over hundreds of millions of years. Continents have formed and then broken apart, and in some instances most of the land surface was concentrated into what have been referred to as supercontinents. For example, during the early Paleozoic there were a considerable number of separate continents, but toward the end of this era most of the land surface had gathered together to form a supercontinent that has been named Pangaea (meaning "all lands"). At that time a large part of what was to become the continent of North America was joined to what are now Africa and portions of Europe. The shapes of these early continental land masses were quite different from what they are at present, as were the relative positions of these land masses on the earth, and the Central Appalachian region was then near the equator. It is interesting to note that during the Carboniferous the region would have been part of what might be considered a single gigantic and largely continuous wetland characterized by the coal swamp forests to be described in chapter 2. In theory, it would have been possible to have walked all the way from what is now Poland, crossing the British Isles, Nova Scotia, and the Central Appalachians, to reach the central United States! During the Permian an interval of mountain building (called the Appalachian orogeny) occurred in eastern North America, transforming what had been a flat region into a range of towering mountains that probably resembled the Himalaya Mountains of today. In addition to the major uplifting, many horizontal layers of rocks underwent extensive folding and thrust faulting (a process by which breaks in the earth's crust cause older layers of rock to be pushed up and over younger layers), which can be observed in road cuts at a number of places in the Central Appalachians (fig. 3). As soon as they were uplifted, these mountains became subject to erosion, and the sediments produced now make up most of the rocks exposed at the surface throughout the region.
During the vast interval of time that has passed since their formation, the mountains produced during the Appalachian orogeny gradually eroded, making slopes less steep, ridges and summits more rounded, and the overall relief (i.e., the variations in elevation over an area of the earth's surface) much less than when the mountains were new. Nevertheless, portions of the region have persisted above sea level for well over 250 million years, and this has been important for several groups of organisms found in the Central Appalachians.
Data from studies of the rate at which erosion occurs indicate that the entire Appalachian system is being lowered by approximately a hundred feet every million years. If this rate had remained the same since the rise of the original Appalachians approximately 300 million years ago, these original mountains would have been almost 30,000 feet tall, which seems highly unlikely. (Mount Everest, currently the highest mountain on the earth, reaches 29,029 feet.) Modern geologists have suggested that instead of being remnants of the original Appalachians, the mountains that we see today actually are no older than the early Cenozoic. The considerable erosion that has taken place seems to have been counterbalanced by concurrent geological uplift that apparently occurs at a rate of at least thirty feet per million years. The presence of rock layers of Cenozoic age at elevations above sixteen hundred feet in parts of the Appalachians seemingly provides clear evidence for such uplifting. There is indirect evidence, derived from the sediment record left as the mountains eroded, that the rate of uplift has varied greatly during the Cenozoic. Many rivers carry sediment eroded from the Appalachians to the Atlantic Ocean and Atlantic Coastal Plain, where it is deposited. These deposits, both onshore and offshore, have been well studied, and it is now possible to determine the volume of sediment deposited during different intervals of time. The most important influence on the amount of sediment deposited at a given time seems to be the amount of erosion taking place in the mountains during that time, which in turn depends largely on the height and steepness of the land surface being eroded. When the mountains are high and their slopes steep, there is more erosion and thus more sediment deposited, while there is less erosion and less sediment when the mountains are lower and their slopes are gentler. By plotting the volume of sediment deposited against time, one can calculate an index of what the topography in the region was like. Relatively little sediment appears to have been deposited during the early and middle Cenozoic, suggesting a landscape with little relief. However, a twentyfold increase in sediment accumulation began approximately twenty million years ago, reaching a peak about fifteen million years (fig. 4). This pattern suggests a considerable increase in relief and therefore in uplift rate. Exactly what caused such a major change in uplift rates is not known.
What all of this means is that the geology of the Central Appalachian region has been a lot more dynamic since the arrival of the first Native Americans more than twelve thousand years ago than might be suggested by the seeming imperturbability of the landscape (apart from changes brought on by certain human activities). The geological record reveals abundant evidence that what we see today is very different from what would have been seen in the distant past (and sometimes the not-so-distant past).
THE ICE AGES About 2.6 million years ago another dramatic geologic event affected the landscape of the Central Appalachians. The earth's climate began to cool, and major ice sheets began to form in northern portions of North America, Europe, and Asia. This was not a unique event, since there have been at least five occasions in the history of the earth when the same type of global cooling took place. Each of these occasions is commonly referred to as an "ice age" (or, more precisely, a "glacial age"). During an ice age, ice sheets form and then expand outward at the margin as more and more ice accumulates. This expansion (or advance) of the ice sheet continues as long as temperatures at the margin are not so high that they melt the ice faster than it arrives. As a result of the long-term variations in temperature that characterize an ice age, the ice sheets advance and then retreat. Glaciations are periods during which global temperatures are low and ice sheets form and advance. The warmer intervals between glaciations, when the ice sheets are limited in extent, are called interglacial periods. For example, there were four major advances (and thus glaciations) during the most recent ice age, with the most recent advance (which has been named the Wisconsin glaciation) reaching its maximum extent about eighteen thousand years ago. It has been estimated that ice then covered about 30 percent of the land surface of the earth and that sea level was about four hundred feet lower than it is today. The sheer size of the large ice sheet (called the Laurentide) that covered much of the northern portion of North America during the Wisconsin Glaciation is difficult to comprehend. At its very largest, the Laurentide ice sheet probably extended over an area of almost six million square miles, with a maximum thickness of more than two miles centered over what is now Hudson Bay.
Ice sheets never covered any of the Central Appalachian region, although the southern margin of the Laurentide ice sheet advanced to within about twenty-five miles of the tip of what is now the northern panhandle of West Virginia. There is little evidence that smaller, localized glaciers ever developed in the higher mountains, although such glaciers did form in the Rocky Mountains in western North America. Nevertheless, the impact of glaciation upon the Central Appalachians was considerable. Because of the proximity of the large ice sheet just to the north, mean annual temperatures throughout the region were as much as 20°F cooler than at present. As a result of these low temperatures, the predominant vegetation was similar to what one finds in present-day Canada. Higher elevations in the Central Appalachians were actually above the tree line and thus would have resembled tundra, a vegetation type that can no longer found anywhere in the region.
Although the Laurentide ice sheet never covered any portion of the Central Appalachians, it did block one of the major northward-flowing rivers, the Monongahela. This river drains a large area of central West Virginia, and the blockage created a large glacial lake, which has been named Lake Monongahela. Much of the area was probably more of a vast mosaic of wetlands and ponds than a lake in the traditional sense, like one of the Great Lakes. In fact, Lake Monongahela has been called an "immense ice-age pond."
Excerpted from A Natural History of the Central Appalachians by Steven L. Stephenson. Copyright © 2013 West Virginia University Press. Excerpted by permission of West Virginia University Press.
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Table of Contents
Chapter 01 Introduction to the Central Appalachians 1
Chapter 02 History of the Flora and Fauna 17
Chapter 03 Plant Life of the Central Appalachians 35
Chapter 04 Forests of the Central Appalachians 51
Chapter 05 Non-Forested Areas of the Central Appalachians 69
Chapter 06 Plants of Special Interest 85
Chapter 07 Lower Plants 101
Chapter 08 Mushrooms and Other Fungi 117
Chapter 09 Non-Insect Arthropods and Other Invertebrates 135
Chapter 10 Insects of the Central Appalachians 153
Chapter 11 Reptiles, Amphibians, and Fishes 167
Chapter 12 Birds and Mammals 185
Chapter 13 Humans in the Central Appalachians 199
Chapter 14 Past, Present, and Future 217
Glossary of Common and Scientific Names 236
Further Reading 242
Figure Credits 248
About the Author 260