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Source Walk: 7-2-95
Petite's Gap, at 2461 feet (750 meters) asl and 37o34' N latitude, lies between two federally-designated wilderness areas, the James River Face and Thunder Ridge to the northeast and southwest respectively. The terrain is moderately rugged and the country rock is Pre-Cambrian layered pyroxene granulite. Major minerals are quartz, plagioclase and potassium feldspars, orthopyroxene, clinopyroxene and magnetite-ilmenite oxides. Garnet, Hornblende and biotite are widespread and apatite and zircon are minor constituents (Rader and Evans, 1993). These constituents, particularly the feldspars, pyroxenes, garnet, hornblende and biotite, provide a considerable variety of mineral nutrients that are not as readily available in the sandstones and quartzites that dominate the western Blue Ridge. These nutrients encourage development of better soils and, as we shall see, a rich and diverse flora.
Traverses were made along the Appalachian Trail for a short distance from the road into each of the Wilderness areas to inventory the flora and as much as possible the local fauna as well. The initial and shortest traverse, about 0.2 miles (300 meters), was made into the James River Face Wilderness. The aspect here is southwest, the forest canopy open and this sunny July day well chosen to acquaint one with light conditions.
Tuliptree (Liriodendron tulipifera) and pignut hickory ( Carya glabra and/or C. ovalis) dominate the canopy, with Northern Red Oak (Quercus rubra) and Black Cherry (Prunus serotina) also common. Less abundant are American Basswood (Tilia americana), Red Maple (Acer rubrum), Bitternut Hickory (Carya cordiformis), Black Walnut (Juglans nigra), and White Ash (Fraxinus americana). There are also scattered White Pine (Pinus strobus), American Chestnut (Castanea dentata) sprouts and small Hackberry, probably Celtis occidentalis. Many trees are of mature size and some Tuliptrees exceed 2 feet (0.6 meters) dbh. From the appearance of these trees, many with side limbs stripped away, it is likely that the canopy was opened up by ice storms. The abundant light that reaches the forest floor as a consequence, set the stage for a rank growth of native shrubs, vines and tall herbs uncharacteristic of typical deciduous forests with more closed canopies. Understory consists of Service Berry (Amelanchier arborea?). Striped Maple (Acer pensylvanicum), Muscletree (Carpinus caroliniana) and Flowering Dogwood (Cornus florida), the latter somewhat diseased, probably by Anthracnose. There is also some Sassafras (Sassafras albidum), which thrives only where light is abundant, and seldom reaches canopy size. The shrub layer is characterized by some species quite demanding of soil conditions. Examples of these are Spice Bush (Lindera benzoin), Black Haw Viburnum (Viburnum prunifolium), Black Raspberry (Rubus occidentalis) and CoralBerry (Symphoricarpos orbiculatus) . However, these are accompanied by the less-demanding Alternate-leaved Dogwood (Cornus alternifolia), Witch Hazel (Hamamelis virginiana), Maple-leaf Viburnum (Viburnum acerifolium) and thorned blackberries. Also reflecting the superior growing conditions are diverse vines including Virginia Creeper (Parthenocissus quinquefolia) (very abundant), Poison Ivy (Rhus radicans), Dutchman's Pipe Vine (Aristolochia macrophylla), Summer Grape (Vitis aestivalis), Canada Moonseed (Menispermum canadense) and several species of Smilax, such as CommonGreenbrier (Smilax rotundifolia) and Carrion Flower (S. herbacea)
Tall herbs favored by the open canopy include many of the aster family Examples are Broad-leaf, Wreath and Wrinkle-leaf Goldenrods (Solidago flexicaulis, S.cæsia and S. rugosa ), Late purple, White Wood, Bigleaf and Wavy-leaf Asters (Asterpatens, A. divaricatus, A.macrophyllus and A. undulatus), Wingstem (Verbesina alternifolia) , Wide-leaved Joe-pye Weed (Eupatorium purpureum), White Snakeroot (E. rugosum), Thin-leaved Sunflower (Helianthus decapetalus), Golden Ragwort (Senecio aureus), Gall-of-the-Earth (Prenanthes sp.) and Wild Lettuce (Lactuca sp.). Tall herbs of other families noted were Black Cohosh ( Cimicifuga racemosa), Jewelweed (Impatiens sp.), Four-leaved Yam (Dioscorea quaternata), Agrimony (probably Agrimonia gryposepala), Lopseed (Phryma leptostachya) in spectacular bloom, Basil Balm (Monarda clinopodia), Horse-balm (Collinsonia canadensis), Spreading Dogbane (Apocynum androsaemifolium) and Virginia Knotweed (Polygonum virginianum). Of intermediate stature were a sanicle ( Sanicula sp.), Wild Columbine (Aquilegia canadensis) in bloom, Whorled Loosestrife (Lysimachia quadrifolia), Enchanters Nightshade (Circaea quadrisuleata), Honewort (Cryptotaenia canadensis), Hairy-jointed Meadow Parsnip (Thaspium barbinode), Plum Lily (Smilacina racemosa) heavy with green berries and much browsed by Deer, Common Many Knees (Polygonatum biflorum), Smooth Sweet Cicely (Osmorhizalongistylis), Golden Alexanders (Zizia sp.), White Avens (Geum canadense) and Dotted St. John's-wort (Hypericum punctatum).
Although most of the small vernal flora had in all likelihood long since been overwhelmed by the later tall growth, remnants were represented by Bloodroot (Sanguinaria canadensis), Mealy Bellwort (Uvularia perfoliata), Great Chickweed (Stellaria pubera ), Wild Geranium (Geranium maculatum) and Virginia Waterleaf (Hydrophyllum virginianum). Where favored by shade or other conditions, late maturing small plants such as Sweet-scented Bedstraw (Galium triflorum), Canada Violet (Viola canadensis) in bloom, Upright Yellow Wood Sorrel (Oxalis stricta) and Rattlesnake Fern (Botrychium virginianum) were also in evidence. However, two species of ground level height, Common Speedwell (Veronica officinalis) and Creeping Five-leaf (Potentilla canadensis/simplex) were confined to a few isolatedpatches of almost bare ground. A plant that deserves special mention here is Green Violet (Hybanthus concolor) representing a monotypic genus in the violet family but in appearance quite unlike a violet. At this season it had already formed its characteristic seed capsules.
Because the bedrock is similar on both sides of Petites Gap, ascent of Thunder Ridge to the southwest provides an opportunity to observe the effects of a northeast aspect. The traverse here is somewhat over a mile from the road to the upper reaches of a strong brook at somewhat over 2800 ft (850 meters) asl. The canopy in the lower Gap at near 2500 ft (760 meters) is dominated by Tuliptree, White Ash, Northern Red Oak and Canada Hemlock (Tsuga canadensis), with the last-named species showing severe defoliation by the Hemlock Wooly Adelgid. Black Locust ( Robinia pseudoacacia ) is also common. Ground cover here consists chiefly of Christmas (Polystichum acrostichoides) and Marginal Shield (Dryopteris marginalis) Ferns, Indian Turnip, (Arisaema triphyllum), Indian Cucumber Root (Medeola virginiana) and Mountain Meadowrue ( Thalictrumclavatum). As we ascend, Hemlock becomes less common and although a number of shrubs and herbs also occur on the other side of the gap, dominance is clearly by a new assemblage. Wild Hydrangea (Hydrangea arborescens ), a shrub, which was not observed on the other side of the gap,becomes prominent as soon as a significant slope is reached. At this season, it was in full bloom and extensively patronized by bumblebees. At perhaps 2600 ft (790 meters) a single shrub of Mountain Holly (Ilex Montana) was encountered, with the relatively low elevation of this occurrence perhaps a response to the northeast aspect and plentiful moisture. From this point the climb successively revealed a small Butternut (Juglans cinerea), a characteristic brilliant black and yellow Appalachian millipede with burnt almond odor (perhaps Sigmoria aberrans), the "Fire Weed" Erechtites hieracifolia, a small Slippery Elm (Ulmus rubra), much Christmas Fern, Cucumber Magnolia (Magnolia acuminata), Maidenhair Fern (Adiantum pedatum), Black Birch, Wild Ginger (Asarum canadense) and the first May Apple (Podophyllum peltatum) of the day. At this point we reached a small muddy seep in which was imprinted the clear track of a Bobcat ( Lynx rufus) accompanied by those of White-tailed Deer (Odocoileus virginianus), including a fawn. Continuing upward we encountered the first Blue Cohosh (Coulophyllum thalictroides) and nearby Goats Beard (Aruncus dioicus) already gone to seed; then a Hairy Sedge, (probably Carex viresens), a flat-coiled land snail shell and Black Walnut. Somewhere here also, perhaps at 2700 ft (820 meters) elevation, Tuliptree practically dropped out and Striped Maple became much more abundant. Then a little higher appeared the first bush of Catawba Rhododendron (Rhododendron catawbiense), perhaps reflecting thinner soils and more rock exposure. As the trail rounded the ridge to a northwest aspect, the first Chestnut Oak (Quercus prinus) was here noted; then, as it turned more easterly again, the first Wild Sarsaparilla (Aralia nudicaulis), always an indicator of cooler conditions.
On further ascent, the soils thinned more and thefirst Rock Fern appeared on exposed rock. However, in a more sheltered enclave of deeper soil just beyond, occurred a single plant of the more demanding American Spikenard (Araliaracemosa). These were followed just above by a few plants of Spotted Wintergreen (Chimaphila maculata) and Wake Bobin (Trillium erectum) which, in the absence of flowers, was identified by its rhombic leaf shape.
Above this level the trail wound to a more easterly aspect through a characteristically mesic community of Hophornbeam, SummerGrape, Poke Milkweed (Asclepias exhaltata) and Purple Bedstraw (Galium latifolium) in bloom. Soon however, the northwest aspect with dry forest was again regained. The canopy here consisted of White Pine,Black Birch, Chestnut Oak, Northern Red Oak and Black Locust. American Chestnut sprouts, Striped Maple, Witch Hazel and Catawba Rhododendron formed understory and shrub layers. An opening on a rocky slope was host to Mountain Laurel, Minnie-bush and Corymed Spiraea (Spiraea betulafolia), with a ground cover of Bowman's Root (Gillenia trifoliata) Fly Poison (Amianthium muscaetoxicum), Wild Sarsaparilla, Wood Tickseed (Coreopsis major), Whorled Loosestrife, Four-leaved Yam, White Wood Aster, an Alumroot (Heuchera sp.), Wild Lily-of-the Valley (Convallaria montana), Marginal Shield Fern, Rock Fern and a lush cover of mosses. From this dry, sunny slope, now in late afternoon, we could hear the roar of the not-too-distant stream ahead, and from the same direction, the calls of Wood Thrushes (Hylocichla mustelina).
Beyond this slope the trail climbs slowly and the forest continues dry and ericaceous with much Chestnut Oak and Laurel. Downy Rattlesnake Plantain (Goodyera pubescens), Galax (Galax aphylla) and Black Gum make their first appearances. A few small Hemlock scattered along the slope show only a little evidence of the Adelgid. Soon we reach the stream that has been sounding for so long. Here the forest is again mesic and open and the stream almost smothered in rank shrubs, vines and herbs which include Mountain Maple (Acer spicatum), an unidentified grape (Vitis sp), Dutchman's Pipe vine, Wood Nettle (Laportea canadensis) and Horse Balm among many other species. A giant Northern Red Oak dominated the scene.
Discussion
A consequence of high mineral nutrient content of the country rock here is floral diversity comparable to limestone regions. A number of species (Black Walnut, Hackberry, Coralberry, Lopseed) that attain their best development in the latter and are quite demanding of soils, also do well here. The ninety or more species recorded during this brief survey indicate that such inventories conducted throughout the growing season would at least double this number in vascular plants alone. The observed diversity is also a consequence of the ample precipitation that characterizes the northern Blue Ridge and the moderate elevations traversed. Only a few plants — Wild Sarsaparilla, Mountain Holly, Striped Maple and Mountain Maple—are truly cold climate species and reflect the modest elevational differences in the area. However their occurrence at the observed elevations may in part be a consequence of aspect and moisture availability.
Abrams et al (1997) studied two stands of old growth forest on Thunder Ridge not far from our inventory sites and which complement our inventories. One stand, dominated by Chestnut Oak, lay on a steep south-facing slope a little above 2574 feet (792 m) asl, while the other, more mesic, with Northern Red Oak dominant, occupied a gently rolling ridge top with a northern aspect a little above 3367 feet (1036 m). Associates in the Chestnut Oak stand were Northern Red Oak, Red Maple, the pignut Carya glabra, Black Gum (Nyssa sylvatica) and minor Black Cherry, Black Birch, Sassafras, White Ash and Striped Maple. The stand dominated by Northern Red Oak was quite diverse, with White Ash, Black Cherry, Black Birch, Yellow Birch (Betula alleganiensis), Sugar Maple (Acer saccharum), Red Maple, American Basswood, Cucumbertree, Canada Hemlock, Bitternut Hickory, the pignut hickory Carya glabra, Mockernut Hickory (Carya tomentosa), Black Locust, White Oak (Quercus alba), Striped Maple, American Chestnut sprouts, Hophornbeam and Witch Hazel. It seems likely to this reporter that the absence of Chestnut Oak in this stand is a consequence of its high elevation and northern aspect (Stephenson et al, 1993), since it is near this species' commonly observed elevational limit. According to the authors"The specific objectives of this study were to characterize the composition, size and age structure, successional development, and tree ring chronologies spanning a 300-year period in the contrasting old-growth Quercus forests." It was found that the history of the Q. rubra stand was complex, with apparent replacement of this dominant species inrecent years by other mesic species, probably as a consequence of fire suppression. In contrast the xeric Q. prinus stand had only a small component of potential oak replacement species and appeared to represent a climax forest on the site on which it occurred. In any case, it was further concluded by the authors that topography and substrate — the latter termed an: "edaphic'" characteristic by them—formed the basis for the contrasting dendroecology and successional development of the two sites. Thus, although excellent studies, such as are exemplified by this one, can reveal much about stand history, they ultimately also confirm fundamental stability relations that are independent of this history (Mueller, 2000).
An additional point of interest here is the presence of this mesic, moisture dependant Northern Red Oak stand on a ridge top. This phenomenon, which, in the experience of this reporter, is common in the Central Appalachians, is in conflict with the common practice of automatically assigning low topographic moisture indexes to such ridge tops. Low moisture is possible on such ridge tops only if run-off or internal drainage is rapid. The presence of abundant moisture on many ridge tops may be seen as a consequence of quite deep, absorbent soils there as a result of favorable geology, and slopes so small that run-off is slow.. Where soils are shallow, slopes steep and rocky, and rock outcrops common, as in the case of the Q. prinus stand, neither moisture nor nutrients can accumulate and a xeric oligotropic flora results.
References
Abrams, Marc D., David A.Orwig and Michael J. Dockry (1997) Dendroecology and successional status of two contrasting old-growth oak forests in the Blue Ridge Mountains, U.S.A. Can Jour For Res, 27, 94-1002.
Mueller, R.F. (2000) Stability Relations in Forests. Forests of the Central Appalachians Project. Virginians for Wilderness Web Site.
Rader, E.K. and N. H. Evans (1993) Geologic Map of Virginia, Expanded Explanation.Virginia Div. of Mineral Resources, Charlottesville, Va.
Stephenson, S.L., A.N. Ash and D.F. Stauffer (1993) Appalachian oak forest, pp 255-233. in Martin, W.H., S.G. Boyce and A.C.Esternacht eds. Biodiversity of the southeastern United States:Upland terrestrial communities and John Wiley and Sons, Inc., New York, 373 p.S