Friday, October 8, 2004

Plant of the Day: White oak, Quercus alba

White oak is the most common oak species in the eastern deciduous forest. It has the largest range of any oak species, ranging from southern Canada to the Gulf and Atlantic Coastal Plains, and west to the eastern Plains. It also occurs in the broadest range of habitats, from moist coves to dry ridgetops. It avoids the wet soils of bottomlands, and, in fact, is absent from the lower Mississippi River Valley. It was a co-dominant with American chestnut on many upland sites before chestnut’s demise. White oak hybridizes readily with many other oak species. Like many other oaks, it is a mast-fruiting species, which means that it produces unusually large acorn crops every 3-5 years. Acorns are gravity-dispersed, with seedlings often germinating near the parent plant, although gray squirrels collecting and stashing acorns for use later in the winter play an important role in seed dispersal. In several oak forests we have ridden through, we have heard that characteristic chatter of gray squirrels in the fall, as they gather nuts for the winter that lies ahead.

West of Cleveland, we rode by Old Woman Creek Sanctuary on Lake Erie. This is the only national estuarine sanctuary in Ohio. Most estuaries are coastal features where inland waterways meet and mix with saltwater, but the term is also sometimes used more generally to refer to places where chemically distinct bodies of water intermingle. The sanctuary includes a diversity of habitats—fresh water marshes, swamp forest, beaches, upland forests, and abandoned agricultural land.

Once we headed away from Lake Erie, south of Cleveland, we began to leave the easier pedaling terrain behind. Ever since eastern Colorado, we have been riding through what is sometimes referred to as the Interior Plains Geologic Province. It is an extensive region of relatively low relief in the mid-section of the continent that has been tectonically stable for more than 500 million years. South of Cleveland, however, we made a significant transition into the western portion of the Appalachian Highlands, where the topography is much more rugged. Although the Appalachians are tectonically stable today, their formation can be traced back to the intense mountain-building processes associated with the collision of two lithospheric plates, somewhat similar to the type of plate convergence responsible for formation of the Himalayas today. As with most mountains, the history of the Appalachians is complex. The initial mountain building began 440-480 million years ago when plates converged and subduction occurred along the plate boundary, resulting in volcanic eruptions and tremendous faulting and folding. Mountain building continued intermittently over the next 250 million years, with more and more land mass gradually being welded onto the edge of the plate, until all the land masses were united into one large supercontinent, known as Pangea. Once the supercontinent broke up about 220 million years ago and the continents began to drift apart, the mountain building forces that had elevated the early Appalachians were quieted and erosive action gradually wore the mountains down. Subsequent uplift during the Cenozoic Era elevated the land, giving the streams more power to cut down through the rock, gradually shaping the dissected landscape we see today in this region.

On the Allegheny Plateau of eastern part of Ohio, we had our last encounter with land that had been glaciated during the Pleistocene. Although this terrain was uplifted as part of the Appalachian mountain building, the ice was able to override the gentler topography of the plateau. We rode across part of one of the Portage Lakes (on a bridge, of course!), a state park that included several kettle lakes formed by disintegrating ice blocks at the end of the last glacial period. Natural lakes are not very common in Ohio. On a geologic time-scale, they are ephemeral landforms, and many of them in this part of the state have already filled in with sediment to form boggy wetlands. We also rode right by Quail Hollow State Park, a little farther along, which includes both a woodland swamp and a sphagnum peat bog, in addition to one depression that is still an open lake. This region provides some nice illustrations of the typical stages of succession that occur as open lakes gradually fill in to form forested wetlands.

After we crossed into Pennsylvania, we rode south through the heart of Raccoon Creek State Park. It is a haven for wildlife, where the patient observer might catch a glimpse of beaver, muskrat, or even mink. The park includes a wildflower reserve along Raccoon Creek. I have visited this reserve in the spring when the wildflowers are in bloom and it is virtually a carpet of color. In rich forests in the East, herbaceous plants that adorn the forest floor flower and set seed early in the spring, while they can still capture abundant sunlight, before the trees leaf out and intercept light that would otherwise reach to the ground. Frankfort Mineral Springs, a collection of small waterfalls and a spring in a grotto formation, is also located in the park. At one time, thousands of visitors came to the spring to take advantage of the purported healing powers of the mineral water.

East of the Monongahela River in southwestern Pennsylvania, we were presented with the rugged topography of the Laurel Highlands, which are part of the Allegheny Mountains—a series of long, parallel, folded mountains with narrow intervening valleys. Here the slopes are pretty steep, but our route cut through the ridges in lower places where we didn’t have to climb quite as high. This area, together with the Ridge and Valley to the east of here, has presented us with some of the more challenging climbs of our cross-country trek—even more so than the Rocky Mountains! The mountains are not as high, but the gradients are steeper in many places. This region includes numerous state parks, including Kooser State Park, which we rode through, as well as the highest point in the state, Mt. Davis.

Between Somerset, Pennsylvania and Cumberland, Maryland, we crossed from the Allegheny Mountains into the Ridge and Valley. In this section, one can easily imagine the extensive compression that pressed long folds into the rocks layers, producing a series of parallel northeast-southwest trending ridges across the region. The effect of the parallel folds is even felt in the regional drainage pattern. Many streams in this area exhibit a “trellis” drainage network, where tributaries flowing down the slopes of the ridges join larger streams running down the intervening valley bottoms at right angles, in a pattern similar to plants on a trellis.

Our route was somewhat circuitous through this area, as the easiest route zigzagged around ridges, since roads tend to follow the lowlands instead of going up over the steep-sided ridges. Nonetheless, we had a lot of climbing to accomplish before we flushed out into the North Mountain in West Virginia.  Farther east, we cut through the Blue Ridge at Harpers Ferry at the confluence of the Potomac and Shenandoah.

Photo taken by Scott Southworth, USGS

Because the Potomac provides a relatively easy way across the Blue Ridge, Harpers Ferry is a town that left a mark on our nation’s history at several key times in the past. The U.S. Arsenal was located there in 1796; it was an important transportation link between the East and the Ohio River Valley; John Brown focused attention on the moral injustice of slavery when he seized the arsenal there in 1859; and during the Civil War it played a critical role, held primarily by Union soldiers, but changing hands many times.

Photo taken by Paul Hackley, USGS