Mid-Appalachian shale barrens
Since 1911 botanists have recognized a habitat type called “shale barren.”  As the name suggests, these are sparsely vegetated sites that occur on shale outcrops where steep slopes, maintained by stream undercutting,  and southern exposures have combined with a porous soil to produce an especially arid habitat that is fire prone.  In the eastern U.S. shale barrens exist as habitat patches scattered from western Virginia, north through eastern  West Virginia, extending on through western Maryland and into neighboring Pennsylvania. 

The habitat is occupied by a flora with conspicuous affinities to the plants of the North American prairie.  Although many of the plant species growing on the shale barrens are found only there—that is to say, they are endemic to this habitat—their closest relatives are found in prairies in the central and western U.S.  

Paleoclimatologists, the scientists who study ancient climates, have abundant evidence from soils and fossils, which  show that the North American prairie extended far into the east during a hot dry period  (the Hypsithermal) that lasted from 8,000 to 4,000 years ago.  Biogeographers  think that when the climate in North America moderated, 4,000 years ago, the prairie withdrew to the west, leaving patches of prairie vegetation in habitat fragments where arid conditions provided summer drought and periodic fires to suppress woody plant survival.

Geographic isolation of the shale barren prairie plants from their relatives further west has allowed them to experience allopatric speciation as they evolved unique characters that they were unable to share with western sister populations.  The shale barren that we visit is above Pads Creek in Bath County, Virginia.  A list of flowering plants endemic to shale barrens is given below.  In 2006 and 2007, we saw clematis blooming, Cades Mountain clover, penstemon, and the scapes of last year’s buckwheat.  On the way home in 2007, we screeched to a halt when Prof. Knox spied a yellow lady’s slipper and several species of Uvularia. 

Allium oxyphilum

 Eriogonum allenii

 Paronychia montana

 Clematis albicoma

 C. coactilis

 C. viticaulis

 Arabis serotina

 Astragalus distortus

 Trifolium virginicum

 Eonothera argillicola

 Pseudotaenidia montana

 Calystegia spithamaea

 Phlox buckleyi

 Antennaria virginica

 Senecio antennariifolius

 Solidago harrisii 

Acid Sinkhole Ponds
On the western side and at the base of the Blue Ridge of the southern Appalachian mountains in Augusta and Rockingham Counties, Virginia, broad fans of  alluvium have eroded from the mountains over the past couple of million years.  The alluvium is made up of cobble, gravel, sand, and clay that give an acid pH to the soil, which lies to a depth of a hundred meters or more upon a bedrock of limestone and dolomite.  As rainwater percolates through the acid soil, it too becomes acid, so when the acid water  reaches bedrock, it erodes the rock creating a sinkhole deep in the earth.  On the surface, the land sinks, giving a shallow depression into which the smallest rock particles collect, forming a grey clay that may be a few meters deep.  The basin of the depression collects rainwater from higher ground around it—that  is, from its watershed.  When evaporation exceeds precipitation and percolation, the basin remains dry; when precipitation exceeds evaporation and percolation, the basin fills with standing water to form a sinkhole pond. 

During dry, warm years the ponds remain dry, while in wet, cool years they accumulate water that may stand to a depth of one or two meters, continuously, for months or a few years.  The clay that lines these sinkhole ponds contains high levels of arsenic that seems to be a natural constituent of the geology. 

Natural standing wetlands are rare in the interior of the mid-Atlantic region; they constitute rare island habitats.  Wetland organisms that have managed to colonize the sinkhole ponds tend to be quite rare, being far from related plants of the same or closely related species.  It looks as though colonization of the ponds have been rare events that have left  successful colonists geographically isolated from their relatives who live in distant wetlands, a situation that is ideal for allopatric speciation.  The unusual hydroperiod and soil chemistry of the ponds reduce competition for organisms able to tolerate them, but the ability to tolerate  these conditions comes at a cost of not being able to compete in more ordinary habitats. 

It is not surprising, then, that some inhabitants of the ponds are endemic to them.  One such endemic plant is Helenium virginicum  (Asteraceae), which is globally endemic to 30 sinkhole ponds in Virginia and disjunct—meaning it has a broad break in distribution—to a cluster of 40 sinkhole ponds in

the Ozarks of Missouri.  Many other plants and  animals are disjunct between the southern Appalachians and the Ozark plateau, presumably because they were driven to extinction in the area between by geological and climatic changes of the Pleistocene (the past 2 million years).

Washington and Lee University back campus
Here we find 80+ acres of forests, fields, and trails where students and members of the community are able to see a good diversity of native and alien plants and communities.  There is a riparian forest corridor along the Maury River, which is in succession from a senescent white pine plantation to a mixed hardwood forest.  Above the floodplain, on a steep north-facing slope, a rich mixed upland hardwood forest must be about 70 years old.  The understory of the hardwood forest is very diverse in its representation of native herbaceous plants.  On the flat upland, above the hardwoods, we find a mix of patches of senescent, planted 50-year-old white pines, scattered with patches of planted 17-year-old loblolly pines, both of  which are being left to undergo succession to hardwoods.  In one of the white pine plantation patches is a one-acre long-term research site, where the patterns and processes of

Alliaria petiolata  (garlic mustard)  invasion are being studied.  Nearby, on an acre site that the university strip mined for soil about 16 years ago, Washington and Lee biologists are in the sixth year of a study of the patterns and processes of invasion resistance.  Here they have planted from seed 62, 3 m X 3 m plots, each with either 3, 12, or 24 species of native grassland species.  Since the summer of 2002, the Washington and Lee biologists have been studying the patterns of spontaneous invasions of the sites by plants and  arthropods, while also studying the physiology of the plants and characterizing microbial and chemical changes occurring in the soil.

House Mountain
Located seven miles west of Lexington, Virginia, House Mountain is actually a pair of peaks, Little House and Big House Mountains, that are at 3222 feet and 3426 feet, respectively.  The peaks are divided by a saddle that stands at 2650 feet elevation.  The saddle contains an old apple orchard and the remains of a farm.  Several other building sites and cabins can be found along the Saddle Ridge Road, a rough jeep trail that runs from the south end of Little House Mountain to the saddle itself.  The mountain has reforested over the last sixty years and is a mixed hardwood forest of hickories, oaks, beeches, locusts, and ash. 

The Spring 2006 Field Biogeography class hiked up Saddle Ridge Road to an old farmsite, where we found the remains of dry-rock walls, with the small stones that suggest cultivated fields.  We identified the remains of the cabin itself, surrounded by spiderwort and lilies of the valley, and we picked medicine bottles and other glass objects out of an old dump at the back of the farmyard.  Eventually, we hiked to the south end of Big House Mountain.

Cole Mountain
Cole Mountain, elevation 3912 feet, stands in the Blue Ridge Mountains in Amherst County, Virginia.  The mountain is an open bald, maintained so by the National Forest Service.  The Appalachian Trail runs across the ridge line of the mountain, north toward Tar Jacket Ridge, south toward Bald Knob (which is, ironically, completely forested).  The hardwoods in the approach hike held a rich understory of flowering plants.  We identified the following species:   Dutchman’s breeches (Dicentra cucullaria ), Cut-leaf toothwort (Cardamine concatenata), spring beauty (Claytonia virginica), Fragaria virginiana, Stellaria media or S. pubera (some dispute on this question).  There are outstanding views from the bald west toward House Mountain, Jump Mountain, and Hogback Mountain.  

Pedlar River District
Southwest of Cole Mountain, along Rt. 60 between the Blue Ridge Parkway and the crossing of the Appalachian Trail at Long Mountain Wayside, the hamlet of Oronoco sits near the Pedlar River.  Our class went to Oronoco Campground, run by the National Forest Service (and part of the George Washington National Forest), where we found marsh marigold (Ranunculaceae) and skunk cabbage (Araceae).  Along Route 60 we saw Pawlonia, Uvularia, dwarf iris, and pinkster.  Later in the term, we visited Statons Creek Falls, nearby and also part of the Pedlar River District.  At the latter place, we identified Saxifraga virginiensis and Aralia nudicaulis (wild sarsaparilla).