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Crow's Nest is a large wilderness area located on the southern border of Stafford County, Virginia, on Potomac Creek. The greater portion of the Crow’s Nest Peninsula is approximately and lies within the coastal plain of Virginia. Virtually the entire Crow’s Nest Peninsula is forested with an impressive, mature stand of mixed hardwoods. Hardwood forests of this extent are becoming increasingly rare in the Virginia and Chesapeake Bay coastal plain due to prevalent forestry practices and fragmentation of natural areas for development and agriculture. The size and continuity of this hardwood stand enhance its viability and its value in providing a large, unfragmented natural area for diverse organisms. Within a relatively short time (50-100) years, this forest will also comprise a substantial occurrence of old-growth forest with inestimable scientific, biological, and aesthetic values. Currently, trees greater than 60 centimeters (2’) diameter at breast height (dbh) are common, and very large relict tree specimens are scattered throughout the site. The entire Crow’s Nest Peninsula is undeveloped and is primarily forested with mature stands of hardwood trees such as oaks and hickories. This is especially true in the eastern half of the peninsula and the northern slopes facing Accokeek Creek. The coastal plain landscape in this region of Virginia was formed beginning in the late Triassic period, approximately 230 million years ago through the rise and fall of the sea. Crow’s Nest is approximately five miles in length from east to west, across and rises above the surrounding Accokeek and Potomac Creeks. The peninsula is also highly dissected on its north and south sides by steep ravines flowing into these two fresh-water tidal creeks. In contrast, most landscapes in the coastal plain of Virginia are relatively flat and/or gently rolling. Crow’s Nest’s dramatic rise to above Potomac and Accokeek Creeks is startling compared to the adjacent peninsulas in Stafford County such as Marlborough Point and Widewater Peninsula are relatively flat. A large portion of Crow’s Nest is composed of calcareous, or calcium rich, soil layers from ocean or marine animals that once lived at the bottom of a vast inland sea. Most soils in the piedmont and coastal plain of Virginia are not calcareous or limey and thus tend to be acidic. This calcareous soil strata within Potomac Creek is referred to as the Aquia Formation, which is 60 million years old. The Aquia Formation is found within a larger outcrop belt known as the Pamunkey Group, a sequence of Lower Tertiary (Paleocene-Eocene) sands and clays that formed in shallow marine environments beneath the western margin of the Atlantic Ocean. The Aquia Formation is composed of marine sediments that are dark green to gray-green, argillaceous, highly glauconitic, well sorted fine-to medium grained sand with shell beds up to in depth. Today, shell-marl/calcareous ravine forests such as those at Crow’s Nest are not common anywhere in the mid-Atlantic region. These plant communities are rare to this coastal plain ecosystem. There are two nutrient-rich plant communities associated with lime sands and localized shell concretions at Crow’s Nest. One can be broadly classified as Basic Mesic Forests (G2, globally imperiled). Another rare community found at Crow’s Nest that is typically associated with the shell-marl/calcareous environments, is the Basic Oak-Hickory Forest (G2, globally imperiled). These are found on two very steep slopes facing Potomac Creek and represent this plant community. Much of the shell-marl/calcareous ravine forests that do still exist on the east coast of the United States have since been heavily logged. In assessing natural communities in need of protection, the Virginia Department of Conservation and Recreation listed the state’s few remaining calcareous ravine forests to be conservation priorities. The Crow’s Nest site is perhaps Virginia’s best remaining example of this rare forest community. Due to the unusual subsurface calcareous soil formations underlying most of the peninsula, the unusual soils are basic (alkaline) and give rise to rare plants and plant communities. This is due to the ability of the limey soils at Crow’s Nest to neutralize and buffer soil pH within the range 6.3 to 6.8. Elements such as calcium (Ca) and magnesium (Mg) create conditions in the soil that raise the pH of the soil and increase nutrient availability for plants. This results in the establishment of more robust and diverse vegetation at Crow’s Nest. Additionally, disjunct plant communities at Crow’s Nest are found that are not common in the piedmont and coastal plain of Virginia as these areas generally have lower pH soils. These rare or “disjunct” plants and plant communities include small-flower baby-blue-eyes (Nemophila aphylla) and glade fern (Athyrium pycnocarpon). After assisting and conducting field surveys for rare plant species and plant communities, the Virginia Department of Conservation and Recreation, Division of Natural Heritage determined in 1999 that “Crow’s Nest is considered one of the finest, if not the finest example of mature forests remaining in the Coastal Plain of Virginia.” These forest communities on the peninsula consist of several distinct community types. The peninsula supports several regionally and globally rare plants and plant communities, two of which are ranked Globally Imperiled (G2) by the Nature Conservancy’s Natural Heritage Program. ==Geologic History of Crow's Nest== The mid-Atlantic Ridge started to form in the early Jurassic period (175 million years ago), breaking apart the super continent Pangaea and beginning the expansion of the modern Atlantic Ocean. It has widened steadily to its present size. This rifting event separated North America from Africa and the area known today as Virginia became the trailing edge of the newly formed North American continent. The Jurassic Period is found in the Mesozoic Era, or the Age of the dinosaurs. The Mesozoic Era spanned a length of time from 251 million years ago to 66 million years ago. In the early Eocene Epoch (55.8 million years ago) the Coastal Plain of Virginia was completely underwater. Sediment accumulating beneath this sea eventually would become the Crow's Nest of today. The Paleocene and the Eocene Epochs are found in the Cenozoic Era, or the age of the mammals. The Cenozoic Era spanned a length of time from 66 million years ago to the present. During the Eocene, the Atlantic Ocean was considerably narrower than it is today, making migration relatively easy for marine animals. The climate of Virginia during this period was considerably warmer than it is today. According to extensive records, the Earth experienced its warmest interval of the past 66 million years during the early Eocene and Virginia was probably much warmer than central and southern Florida today. The remains of large alligators and turtles have been found at this latitude in Virginia. The calcareous soil strata within Potomac Creek, the Aquia Formation, is 60 million years old. This formation is found within a larger outcrop belt known as the Pamunkey Group, a sequence of Lower Tertiary (Paleocene-Eocene, 55.8 million years ago) sands and clays that formed in shallow marine environments beneath the western margin of the Atlantic Ocean. The Aquia Formation is composed of marine sediments that are dark green to gray-green, argillaceous, highly glauconitic, well sorted, fine-to medium-grained sand with shell beds up to in depth. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crow's Nest, Stafford County, Virginia」の詳細全文を読む スポンサード リンク
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