Introduction
An attempt is made here to fill out our picture of the Central Appalachian forests by a survey of their northern reaches, a part of which includes the new element of glaciated terrain. In so doing all available data on the floras, the geologic substrates and climatic characteristics will be drawn upon. Attention is directed to the continuity of these characteristics on the Allegheny Mountains and Plateau from northwestern Pennsylvania to east central West Virginia and adjacent Virginia. This continuity is expressed most fundamentally in the geologic base with its flat - lying or slightly folded sedimentary beds, and climatic characteristics - even to a similarity of mean air temperatures at a given elevation through the considerable change in latitude. By contrast, the Ridge and Valley and Blue Ridge Provinces exhibit considerable change with latitude, and in the case of the Blue Ridge, attenuation and disappearance as South Mountain (Figure 1). The Ridge and Valley Province exhibits not only a great broadening, but a drastic change in direction of its sharply - folded and faulted mountain ranges in passing from Virginia to central Pennsylvania. As in West Virginia and Virginia, the mean and generally even maximum elevations of this Province lie considerably below those of the Alleghenies. As in these states, there is considerably more variation in the exposed Ridge and Valley rocks and the resultant soils than in those of the Allegheny Mountains and Plateau. In the former there is a systematic concentration of erosion - resistant sandstones, conglomerates and quartzites capping the linear ridges and less resistant limestones and shales in the intervening valleys.
Unlike those of the Alleghenies, mean isotherms in Pennsylvania's Ridge and Valley do not run SW - NE. Instead they curve toward the east, running roughly parallel to the strike of the fold mountains. Thus, within this Province, there is a marked decline from Virginia to central Pennsylvania in air and soil temperatures at a given elevation and aspect. Additionally, the northern Pennsylvania Ridge and Valley is relatively cloudy, although not to the degree of the region of the cloudy - day maximum (Reifsneider and Lull, 1965). These characteristics, as we shall see, are reflected in the distribution of species throughout the region.
Southwestern Pennsylvania contains the unique feature of the slender salient of high Allegheny Mountains that connects the broad Allegheny Plateau of Northwestern Pennsylvania with the great complex of even higher mountains and plateaus of eastern West Virginia and adjacent Virginia. The position of this connecting salient sets up at least the possibility of it having acted in the past as a migration corridor for northern - high - elevation species of plants and animals and its continued use for this purpose by species threatened by human developments and by global warming.
Worthy of special mention also is the Pocono Plateau, which includes glaciated terrain. There, many lakes, extensive acidic wetlands and unusual mesic shrublands evolved in response to disruption of the drainage by both Illinoian and Wisconsinan glaciers. Although at relatively low elevations, the resulting high water tables, in combination with local cool summer temperatures and high precipitation, have given rise to rich flora and fauna of northern species, many of which are at the southern limits of their ranges (Latham et al, 1996).
Plant Communities Summary
A review of Pennsylvania plant communities was provided by Fike (1999), based in part on the work of Smith (1991). The following general categories were presented:
1 Terrestrial Forests
2 Palustrine Forests
3 Terrestrial Woodlands
4 Palustrine Woodlands
5 Terrestrial Shrublands
6 Palustrine Shrublands
7 Terrestrial Herbaceous Openings
8 Herbaceous Wetlands
9 Community ComplexesIn what follows we discuss the floras of a number of representative habitats and taxa which have, through numerous surveys, been found to occur in these habitats and are held as voucher specimens in herbaria. The precise locations of the taxa on maps have been fixed by the latitude and longitude coordinates of the locations where the collections were made (Wherry et al, 1979; Rhoads and Klein, 1993). Since these collections extended through a considerable time period, some taxa may no longer occur where originally collected. Also, the absence of a taxon at a particular location in no way signifies that it is unstable, or in fact does not occur at the location Not only does the principle of conditional absence (Mueller, 2000) apply, but the specimen may simply not have been collected or even noted.
Pennsylvania vegetation originally was and still is dominated by closed canopy upland forests of category 1 above. Perhaps next in importance are the palustrine closed canopy forests of category 2. These are followed in importance by the woodlands, which grade into open canopy upland forests included in category 1. In comparison with the foregoing, the shrublands, herbaceous openings and wetlands occupy relatively small areas. In what follows only brief mention or summaries are provided for those plant communities that are similar to those-and occupy the same general habitats- in Virginia and West Virginia Examples are the major upland forest types (except as incidentally discussed), ridge-top acidic barrens and flood plain communities. However, some communities, such as the boreal wetlands and till barrens, which are not found southward, are dscussed in some detail and compared with their nearest equivalents farther south.
Still the most comprehensive summary and analysis of the Pennsylvania and adjacent New York closed canopy forests is that of Lucy Braun (1950). Utilizing the data of Lutz (1930), Lutz and McCombe (1935), Hough (1936), Gordon (1937 and 1940) and Hough and Forbes (1943). She discussed and compared the different facies of the Hemlock - White Pine - Northern Hardwoods of the Allegheny Plateau. These forests were dominated by Canada Hemlock ( Tsuga canadensis), American Beech (Fagus grandifolia ), Red and Sugar Maples (Acer rubrum and A. saccharum ) and to a lesser degree, by White Pine (Pinus strobus), Yellow and Black Birches (Betula alleghaniensis and B. lenta), American Basswood (Tilia americana), Black Cherry (Prunus serotina) and American Chestnut (Castanea dentata).
Quite generally, these forests had shrub and herbaceous floras rich in northern as well as Appalachian species that we have already encountered at higher elevations and in cool valleys in West Virginia and Virginia. Common shrubs and small understory trees were Hobblebush (Viburnum alnifolium) and Mountain Holly (Ilex montana), and these were accompanied by such herbs as Canada Mayflower (Maianthemum canadense), White Wood Sorrel (Oxalis montana), Star Flower (Trientalis borealis) and Mountain Aster (Aster acuminatus), as well as others to be discussed later.
Braun drew attention to subtle differences between forest stands on the Allegheny Plateau, such as those at East Tionesta Creek and Heart's Content and others such as the Cook Forest and that at Ricketts Glen, at the Plateau edge. In the two last mentioned more characteristically southern species such as White Oak (Quercus alba) and Tuliptree (Liriodendron tulipifera) were more prominent. Of interest also was the occurrence in these forests of the more nutrient - demanding White Ash (Fraxinus americana). While this species was present in low frequencies at East Tionesta Creek and Ricketts Glen, where Sugar Maple was also prominent, it did not occur or was present in only trace amounts at Heart's Content and Cook Forest, where Red Maple greatly outranked Sugar Maple. These associations are consistent with the relative stabilities of these species with respect to pH and the base - content of the soils.
While also dominated by White Pine - Hemlock Northern Hardwoods closed - canopy forests, the glaciated northeast and the Pocono Plateau are quite different from the northwest Alleghenies, particularly with respect to the abundant lakes, ponds, wetlands and shrub barrens in the former regions. They also present an interesting juxtaposition in places of boreal and Southern and Central Appalachian species
Although in many ways indistinguishable from their Virginia and West Virginia counterparts, the Oak - Chestnut Forests that dominate Pennsylvania's great central Ridge and Valley region exhibit subtle differences. As pointed out previously, isotherms there run roughly east and west, so there is a marked decrease in temperatures with latitude Thus species that typically occur at high elevations in the Virginia and West Virginia Ridge and Valley region occur at lower elevations in that of Pennsylvania. In Pennsylvania Early Low Blueberry (Vaccinium angustifolium), a northerner, is found at relatively low elevations and competes with Upland Low Blueberry (V. pallidum), the dominant upland species at all but quite high elevations in Virginia. In one case, in the Seven Mountains area, near the center of Pennsylvania, the Bear Meadows Bog boasts a mix of Appalachian and boreal species that includes the farthest south - ranging Black Spruce (Picea mariana) at an elevation of only 1820 feet asl. Also, a number of familiar Virginia species such as Galax (Galax aphylla), Southern Bellflower (Campanula divaricata), Catawba Rhododendron (Rhododendron catawbiense ) and Southern Mountain Cranberry (Vaccinium erythrocarpum), that occur over a wide range in latitude and elevations, including at the highest elevations, do not occur at all in Pennsylvania. Here subtle effects independent of temperature but sensitive to other effects of latitude may be involved.
Glaciated Northwest Allegheny Forest and Wetlands
Although the glaciated northwest Allegheny region does not exhibit the pervasive interrupted drainage and extensive wetlands of the northeast and Pocono Plateau, there are a few centers of diversity rich in disjunct boreal species. One of these centers is a complex of bogs and alluvial wetlands in the northwest corner of Warren County. Of particular interest is the Columbus Bog on State Gamelands 197, which contains bog ponds formed by the melting of residual ice blocks of the retreating Wisconsinan glacier (Fike, 1999). The area is one of low relief and not at a high elevation, with the Bog lying above the 500 meter contour, which separates it from the lower part of the drainage to the west. Bedrock in the Bog area is dominated by Devonian Chadakoin Formation, which consists of light gray and brownish siltstone and sandstone interbedded with medium gray shale. However the most common rock in the uplands is Devonian Venango Formation consisting of light gray siltstone interbedded with bluish - gray shale and flaggy gray sandstone. Panama Conglomerate and Woodstock Sandstone respectively define the lower and upper limits of the Formation (Berg et al, 1980). Rocks in the region are generally flat - lying or with a small dip of their beds. While the rocks all appear to be dominantly siliceous, the common occurrence of marine fossils hints at the possibility of local Ca / Mg - rich beds. Also, glacial till may be a source of these bases. The persistence here of a boreal flora is also favored by the coincidence of a unique local mean yearly temperature minimum and precipitation maximum astride the Warren - Erie County line in close proximity to the wetlands (Hough and Forbes, 1943).
The following is a breakdown into habitat types of plant taxa documented and listed by Rhoads and Klein (1993) as located in the extreme northwest section of Warren County in the immediate vicinity of the wetland complex. referred to above. Non-native taxa and crosses are omitted. It should be noted that a given taxon may not actually have originated in the habitat to which it is assigned, since many taxa occupy several habitat types. However the habitat chosen for a taxon is generally found to be most characteristic. It should also be remembered that there is a tendency to omit mention of the more common species in the enveloping forest of rare habitats such as wetlands.
First listed are taxa most typical of the Braun's Hemlock - White Pine - Northern Hardwoods, a typically mesic forest type. Secondly are listed taxa typical of the more xeric Oak - Chestnut forest type. These are followed successively by taxa of Marsh - Open Water Type, Wet Meadow - River Bottom Type, Base - rich Wetland Type and Acid Bog Type. Taxa are listed in order of life form. Those marked with an asterisk are of special interest because they have not been observed to range south into West Virginia and Virginia.
Hemlock - White Pine - Northern Hardwoods taxa, regarded as forming the enveloping upland forest of the region.
Pinus strobus (White Pine)
Tsuga canadensis (Canada Hemlock)
Fagus grandifolia (American Beech)
Betula alleghaniensis (Yellow Birch)
Tilia americana (American Basswood)
Prunus serotina (Black Cherry)
Acer rubrum (Red Maple).
Acer saccharum (Sugar Maple)
Carpinus caroliniana (Muscletree)
Populus tremuloides (Trembling Aspen)
Amelanchier laevis (Smooth Serviceberry)
Prunus pensylvanica (Fire Cherry)
Prunus virginiana (Choke Cherry)
Sorbus americana (Mountain Ash)
Acer spicatum (Mountain Maple)
Taxus canadensis (Canada Yew)
Hamamelis virginiana (Witch Hazel)
Corylus americana (American Hazelnut)
Ribes glandulosum (Skunk Currant)
Ribes triste (Wild Red Currant)
Ribes americanum (Wild Black Currant)
Cornus alternifolia (Alternate-leaved Dogwood)
Viburnum acerifolium (Maple-leaf Viburnum)
Viburnum alnifolium (Hobblebush)
Viburnum lentago (Nannyberry)
Diervilla lonicera (Bush Honeysuckle)
Lonicera canadensis (Fly Honeysuckle)
Lonicera dioica (Smooth Honeysuckle)
Clematis virginianum (Virgin's Bower)
*Euonymus obovatus (Running Strawberry)
Vitis aestivalis (Summer Grape)
Cornus canadensis (Bunchberry)
Lycopodium flabelliforme (Ground Pine)
Lycopodium lucidulum (Shining Clubmoss)
Lycopodium annotinum (Stiff Clubmoss)
Lycopodium obscurum (Tree Clubmoss)
Equisetum sylvaticum (Wood Horsetail)
Botrychium dissectum (Cut-leaf Grape-fern)
Botrychium laceolatum (Lance-leaf Grape-fern)
Botrychium matricariaefolium (Camomile Grape-fern)
Botrychium oneidense (Blunt-lobed grape-fern)
Botrychium virginianum (Rattlesnake Fern)
Ophioglossum pusillum (Northern Adder's Tongue)
Adiantum pedatum (Maidenhair Fern)
Dennstaedtia punctilobula (Hay-scented Fern)
Thelypteris noveboracensis (New York Fern)
Asplenium platyneuron (Ebony Spleenwort)
Athyrium filix-femina var angustum (Northern Lady Fern)
Dryopteris carthusiana (deciduous Spinulose Shield Fern)
Dryopteris goldiana (Goldie's Shield Fern)
Dryopteris intermedia (Intermediate Shield Fern)
Dryopteris marginalis (Marginal Shield Fern)
Dryopteris disjuncta (Oak Fern)
Polytrichum acrostichoides (Christmas Fern)
Asarum canadense (Wild Ginger)
Actaea pachypoda (White Baneberry)
*Actaea rubra (Red Baneberry)
Cimicifuga racemosa (Black Cohosh)
Hepatica acutiloba (Sharp-lobe hepatica)
Ranunculus abortivus (Kidney-leaf Buttercup)
Ranunculus recurvatus (Hooked Crowfoot)
Thalictrum dioicum (Early Meadowrue)
Caulophyllum thalictroides (Blue Cohosh)
Dicentra canadensis (Squirrel Corn)
Laportea canadensis (Wood Nettle)
Claytonia caroliniana (Carolina Springbeauty)
Silene alba (White Campion)
Viola canadensis (Canada Violet)
Viola pubescens (Downy Yellow Violet)
Viola rostrata (Long-spurred Violet)
Viola rotundifolia (Round-leaved Violet)
Viola sororia (Downy Wood Violet)
*Mitella nuda (Miterwort)
Tiarella cordifolia (Foamflower)
Dalibarda repens (Star-violet)
Fragaria virginiana (Virginia Strawberry)
Waldsteinia fragarioides (Barren Strawberry)
Vicia carolina (Wild Vetch)
Oxalis montana (White Wood Sorrel)
Oxalis stricta (Upright Yellow Wood Sorrel)
Geranium maculatum (Wild Geranium)
Floerkea proserpinacoides (False-mermaid)
Aralia nudicaulis (Wild Sarsaparilla)
Panax trifolius (Dwarf Ginseng)
Cryptotaenia canadensis (Honewort)
Osmorhiza claytoni (Hairy Sweet Cicely)
Sanicula canadensis (Black Snakeroot)
Sanicula marilandica (Maryland Sanicle)
Sanicula trifoliata (Trifoliate Sanicle)
Thaspium barbinode (Hairy-jointed Meadow Parsnip)
Apocynum androsaemifolium (Spreading Dogbane)
Phlox divaricata (Wild Blue Phlox)
Polemonium reptans (Greek Valerian)
Hydrophyllum canadense (Broad-leaved Waterleaf)
Hydrophyllum virginianum (Virginia Waterleaf)
Mertensia virginica (Virginia Cowslip)
Pedicularis canadensis (Wood Betony)
Veronica officinalis (Common Speedwell)
Galium triflorum (Sweet-scented Bedstraw)
Mitchella repens (Partridgeberry)
Aster acuminatus (Mountain Aster)
Aster divaricatus (White Wood Aster)
Aster schreberi (Schreber's Aster)
Lactuca biennis (Blue lettuce)
Solidago nemoralis (Old Field Goldenrod)
Arisaema triphyllum (Indian Turnip)
Carex albursina
Carex aquatili
Carex arctata
Carex blanda
Carex brunnescens
Carex cephalophora
Carex crinita
Carex debilis
Carex gracillima
Carex intumescens
Carex laxiflora
Carex leptonervia
Care novae-angliae
Carex plantaginea
Carex radiata
Carex rosea
Brachyelytrum erectum (Bearded Shorthusk)
Glyceria melicaria (Slender Manna Grass)
Milium effusum (Millet Grass)
Poa alsodes
Poa saltuensis
Allium tricoccum (Ramps)
Clintonia borealis (Yellow Clintonia)
Disporum lanuginosum (Hairy Disporum)
Maianthemum canadense (Canada Mayflower)
Medeola virginiana (Indian Cucumber-root)
Smilacina racemosa (Plume Lily)
Trillium grandiflorum (Large-flowered Trillium)
Trillium undulatum (Painted Trillium)
Uvularia perfoliata (Mealy Bellwort)
Smilax herbacea (Carrion Flower)
Cypripedium calceolus var pubescens (Large Yellow Ladyslipper)
Orchis spectabilis (Showy Orchis)
Spirathes ochroleuca (Yellow Nodding Lady's Tresses)
Habenaria fimbriata (Large Purple Fringed Orchid)
Dry, Rocky, Open Forest Facies
Quercus prinus (Chestnut Oak)
Nyssa sylvatica (Black Gum)
Gaylussacia baccata (Black Huckleberry)
Rhododendron nudiflorum (Pink Azalea)
Rhododendron roseum (Mountain Azalea)
Vaccinium pallidum ( Upland Low Blueberry)
Lycopodium tristachyum (Slender Ground Pine)
Pteridium aquilinum (Bracken Fern)
Chimaphila umbellata (Pipsissewa)
Pyrola elliptica (Shinleaf)
Aronia prunifolia (Purple Chokeberry)
Epilobium angustifolium (Fireweed)
Oenothera perennis (Sundrops)
Comandra umbellata (Bastard Toadflax)
Aralia hispida (Bristly Sarsaparilla)
Anaphalis margaritacea (Pearly Everlasting)
Antennaria plantaginifolia (Plantain-leaf Pussytoes)
Aster novae-angliae (New England Aster)
Aster pilosus (Heath Aster)
Juncus tenuis (Trail Rush)
Carex communis (Fiberous-root Sedge)
Carex normalis
Carex swanii (Swan Sedge)
Carex virescens (Ribbed Sedge)
Agrostis perennans (Autumn Bent Grass)
Danthonia spicata (Poverty Oat Grass)
Muhlenbergia mexicana (Mexican Muhly)
Panicum acuminatum (a panic grass)
Cypripedium acaule (Pink Ladyslipper)
Marsh, Open Water
Thelypteris palustris (Mash Fern)
Nuphar lutea (Cowlily)
Brasena schreberi (Watershield)
Caltha palustris (Marsh Marigold)
Potamogeton epihydrus (Floating Pondweed)
Potamogeton foliosus (Leafy Pondweed)
*Potamogeton natans (Floating Pondweed)
*Calla palustris (Wild Calla)
Peltandra virginica (Arrow Arum)
Lemna minor (Least Duckweed)
Phalaris arundinacea (Reed Canary Grass)
Phragmites australis (Common Reed)
Typha latifolia (Common Cattail)
Dulichium arundinaceum (Three-way Sedge)
Iris versicolor (Blue Flag)
Wet Meadows and River Bottoms
Abies balsamea (Balsam Fir)
Salix nigra (Black willow)
Quercus bicolor (Swamp White Oak)
Salix cordata (Heartleaf Willow)
Salix discolor (Pussy Willow)
Salix interior (Sandbar Willow)
Salix sericea (Silky Willow)
Alnus rugosa (Speckled Alder)
Spiraea alba (Pipestem)
Cornus amomum (Silky Dogwood)
Cornus racemosa (Gray Dogwood)
Cornus stolonifera (Red Osier Dogwood)
Ilex verticillata (Winterberry Holly)
Viburnum trilobum (Highbush Cranberry)
Equisetum arvense (Meadow Horsetail)
Osmunda cinamomea (Cinnamon Fern)
Osmunda claytoniana (Interrupted Fern)
Dryopteris cristata (Crested Shield Fern)
Onoclea sensibilis (Sensitive Fern)
Polygonum arifolium (Halberd-leaved Tearthumb)
Polygonum punctatum (Water Smartweed)
Polygonum sagittatum (Arrowleaf Tearthumb
Cardamine bulbosa (Bulbous Cress)
Saxifraga pensylvanica (Swamp Saxifrage)
Hypericum punctatum (Dotted St. Johns Wort)
Viola cucullata (Marsh Blue Violet)
Ludwigia palustris (Marsh Purslane)
Angelica atropurpurea (Purple Angelica)
Cicuta bulbifera (Bulbiferous Water hemlock)
Hydrocotyle americana (American Water Penny-wort)
Sium suave (Water Parsnip)
Verbena hastata (Blue Vervain)
Lycopus uniflorus (Northern Bugle Weed)
Scutellaria lateriflora (Mad-dog Skullcap)
Mimulus ringens (Common Monkey flower)
Veronica scutellata (Marsh Speedwell)
Galium asprellum (Rough Bedstraw)
Galium palustre (Palustrial Bedstraw)
Galium tinctorium (Clayton's Bedstraw)
Aster prenanthoides (Crooked-stem Aster)
Aster puniceus (Purple-stem Aster)
Aster umbellatus (Flat-top White Aster)
Bidens cernua (Nodding Beggar-tick)
Circium muticum (Swamp Thistle)
Eupatorium fistulosum (Common Joe-pye Weed)
Eupatorium maculatum (Mottled Joe-pye Weed)
Eupatorium perfoliatum (Boneset)
Euthamia graminifolia (Grass-leaved Goldenrod)
Gnaphalium uliginosum (Low Cudweed)
Helenium autumnale (Yellow Sneezeweed)
Senecio aureus (Golden Ragwort)
Solidago canadensis (Canada Goldenrod)
Solidago gigantea (Late Goldenrod)
Solidago patula (Rough Goldenrod)
Solidago rugosa (Wrinkled-leaf Goldenrod)
Symplocarpus foetidus (Skunk Cabbage)
Juncus canadensis (Canada Rush)
Juncus effusus (Soft Rush)
Carex comosa
Carex gynandra
Carex interior
Carex laevivaginata
Carex lupulina
Carex lurida
Carex prasina
Carex scabrata
Carex scoparia
Carex seorsa
Carex stipata
*Eriophorum gracile (Slender Cotton Sedge)
*Eriophorum viridicarinatum (Thin-leaf Cotton Sedge)
Eriphorium virginicum (Tawny Cottonsedge)
Scirpus atrovirens
Scirpus cyperinus (Wool Grass)
*Alopecurus aequalis (Short-awned Foxtail)
Calamagrostis canadensis (Blue Joint Grass)
Cinna arundinacea (Wood Reed Grass)
Cinna latifolia (Drooping Wood Reed Grass)
Glyceria canadensis (Rattlesnake Grass)
Glyceria grandis (American Manna Grass)
Leersia oryzoides (Rice Cutgrass)
Lilium canadense (Canada Lily)
Smilacina stellata (Starflower 2)
Veratrum viride (White Hellebore)
Sisyrinchium angustifolium (Blue-eyed Grass)
Habenaria lacera (Ragged Fringed Orchid)
Habenaria psycodes (Purple Fringed Orchid)
Base-rich Wetland
Fraxinus nigra (Black Ash)
Rhamnus alnifolia (Alder-leaf Buckthorn)
Geum rivale (Purple Avens)
Sanguisorba canadensis (Canadian Burnet)
Carex prairia (Prairie Sedge)
Eleocharis intermedia (Matted Spikerush)
Juncus nodosus (Knotted Rush)
Acid Bog
Larix laricina (Tamarack)
Aronia arbutifolia (Red Chokeberry)
Aronia melanocarpa (Black Chokeberry)
Decodon verticillatus (Water Loosestrife)
Nemopanthus mucronata (Mountain Holly)
Andromeda glaucophylla (Bog Rosemary)
*Chamaedaphne calyculata (Leatherleaf)
Gaultheria hispidula (Creeping Snowberry)
*Ledum groenlandicum (Labrador Tea)
Vaccinium crymbosum (Highbush Blueberry)
Vaccinium macrocarpon (Large Cranberry)
Vaccinium oxycoccos (Small Cranberry)
Osmunda regalis (Royal Fern)
Woodwardia virginica (Virginia Chain fern)
Sarracenia purpurea (Pitcher Plant)
Drosera rotundifolia (Round-leaf Sundew)
Viola pallens (Northern White Violet)
Bartonia virginica (Yellow Screwstem)
Scheuchzeria palustris (Podgrass)
Carex atlantica
Carex canescens
*Carex disperma
Carex folliculata
Carex leptalea
Carex trisperma (Three-seeded Sedge)
Carex tuckermanii
Rhynchospora alba (White Beakrush)
Corallorhiza trifida (Early Coral-root)
Cypripedium reginae (Showy Lady's Slipper)
Listera australis (Southern Twayblade)
Habenaria blephoriglottis (White Fringed Orchid)
Habenaria clavellata (Small Green Wood Orchid)
Habenaria flava (Pale Green Orchid)
*Habenaria hyperborea (Northern Green Orchid)
Pogonia ophioglossoides (Rose Pogonia)
It should first of all be noted that not all taxa listed for a given habitat type necessarily form stable associations with each other. In terms of stability diagrams (Mueller, 2000) they cannot be expected to be represented by a single point or even a small volume in multicomponental space. For example, Partridge Berry probably does not form a stable association with Carex albursina, in the Hemlock-White Pine-Northern Hardwood Forests, nor Balsam Fir with Carex interior in Wet Meadows and River Bottoms, although the stability relations of these taxa have not been worked out. More established are the gross stability relations that support the assignment of certain taxa to the broad habitat types. Thus we may have a high degree of assurance that Tamarack does not form a stable association with Sugar Maple, although it may form one with Red Maple. In an extreme example we know that the Acid Bog species Labrador Tea is never found with the dry forest species Chestnut Oak, despite the demand of both for acidic soils.
As a consequence of our choice of location in a region of relatively cool and moist climate, all habitats are relatively rich in taxa with northern distributions, and that are found southward only at higher elevations, in deep mountain valleys or in certain other cool microhabitats. Examples are Trembling Aspen, Mountain Ash, Skunk Currant, Bunchberry, White Wood Sorrel, Mountain Aster, Carex brunnescens, Millet Grass and Canada Mayflower. Some, like Star Violet (Dalibarda repens), may be found as isolated occurrences far south of their normal ranges (Ogle, 1982), particularly in wetlands. An example of a boreal component in a Virginia Appalachian Hemlock-White Pine Hardwood Forest occupying a deep valley is that at Ramsey's Draft (see our section on this occurrence). Examples are particularly common in Acid Bogs, in which Bog Rosemary has an isolated population as far south as the Cranberry Botanical Area in the Monongahela National Forest of West Virginia, while other demanding species, such as Small Cranberry and Early Coral-root, have more common populations in the same general region. As indicated previously, some boreal taxa, here distinguished by an asterisk, do not have outposts as far south as West Virginia and Virginia It is likely that the failure of Labrador Tea to occur in even the coolest habitats southward, such as the Monongahela's Cranberry Botanical Area, Dolly Sods and other like areas in West Virginia's High Alleghenies, is a result, not of climate or of unsuitable habitat, but of the natural depauperization that is to be expected at the edge of community ranges.
Tamarack Swamp
The Tamarack Swamp Natural Area is located in the northwest corner of Clinton County on the unglaciated Allegheny Plateau. Bedrock in the immediate vicinity of the Swamp is Devonian Catskill Formation grayish sandstone, siltstone and shale, with units of gray sandstone in the upper part. Immediately to the south is Mississippian / Devonian Huntley Mountain Formation, which consists of greenish-gray and light olive-gray, flaggy, fin-grained sandstone with a few red shale interbeds (Berg et al, 1980). The elevation of the Swamp is a little below 400 meters (1300 feet) asl and relief in the vicinity exceeds 150 meters (490 feet). The swamp occupies part of the headwaters of Drury Run, a beautiful high-gradient stream that drains southward.
In what follows, and using the same procedures as in our previous descriptions, we allot taxa, obtained from the compilations of Rhoads and McKinley (1993 )from the immediate vicinity of the Swamp, to the two broad habitats "Swamp and Moist Openings" and "Dry to Mesic Forests and Openings."
Swamp and Moist openings
Abies balsamea (Balsam Fir)
Larix laricina (Tamarack)
*Picea mariana (Black Spruce)
Picea rubens (Red Spruce)
Salix sericea (Silky Willow)
*Chamaedaphne calyculata (Leatherleaf)
Rhododendron maximum (Great Rhododendron)
Vaccinium macrocarpon (Large Cranberry)
Vaccinium myrtilloides (Sauertop Blueberry)
Aronia melanocarpa (Black Chokeberry)
Rubus hispidus (Bristly Dewberry)
Cornus racemosa (Gray Dogwood)
Viburnum cassinoides (Wild Raisin)
Thelypteris palustris (Marsh Fern)
Dryopteris cristata (Crested Shield Fern)
Onoclea sensibilis (Sensitive Fern)
Coptis groenlandica (Goldthread)
Polygonum sagittatum (Arrow-leaf Tearthumb)
Hypericum mutilum (Dwarf St. Johns-wort)
Triadenum fraseri (Marsh St. Johns-wort)
Sarracenia purpurea (Pitcher Plant)
Viola cucullata (Marsh Blue Violet)
Verbena hastata (Blue Vervain)
Lycopus uniflorus (Northern Bugleweed)
Scutellaria lateriflora (Mad-dog Skullcap)
Mimulus ringens (Square-stemmed Monkeyflower)
Galium asperellum (Rough Bedstraw)
Galium tinctorium (Clayton's Bedstraw)
Aster puniceus (Purple-stem Aster)
Aster umbellatus (Flat-top White Aster)
Bidens cernua (Nodding Beggartick)
Bidens frondosa (a beggartick)
Cirsium muticum (Swamp Thistle)
Euthamin graminifolia (Grass-leaved Goldenrod)
Gnaphalium uliginosum (Marsh Cudweed)
Arisaema triphyllum (Iindian Turnip)
Juncus effusus
Carex atlantica
Carex echinata
Carex folliculata
Carex gynandra
Carex intumescens
Carex lurida
Carex scabrata (Rough Sedge)
Carex tribuloides
Eleocharis obtusa (Blunt Spikerush)
Eriophorum virginicum (Tawny Cottonsedge)
Scirpus cyperinus
*Glyceria borealis (Small Floating Mannagrass)
Glyceria canadensis (Rattlesnake Grass)
Glyceria striata (Fowl Mannagrass)
Panicum clandestinum (Deertongue Grass)
Sparganium americanum (Common Burr-reed)
Habenaria lacera (Ragged Fringed Orchid)
Dry to Mesic Forests and Openings
Pinus rigida (Pitch Pine)
Pinus strobus (White pine)
Quercus rubra (Northern Red Oak)
Betula lenta (Black Birch)
Prunus serotina (Black Cherry)
Acer saccharum (Sugar Maple)
Amelanchier arborea (Downy Serviceberry)
Crataegus coccinea (Red-fruited Hawthorn)
Sorbus americanus (Mountain Ash)
Acer spcatum (Mountain Maple)
Taxus canadensis (Canada Yew)
Salix humilis (Upland Willow)
Kalmia latifolia (Mountain Laurel)
Rhododendron roseum (Mountain Azalea)
Vaccinium angustifolium (Early Low Blueberry)
Vaccinium pallidum (Upland Low Blueberry)
Vaccinium stamineum (Deerberry)
Rubus strigosus (Red Raspberry)
Dirca palustris (Leatherwood)
Cornus canadensis (Bunchberry)
Gaultheria procumbens (Teaberry)
Lycopodium annotinum (Stiff Clubmoss)
Lycopodium obscurum (Tree Clubmoss)
Osmunda cinnamomea (Cinnamon Fern)
Osmunda claytoniana (Interrupted Fern)
Osmunda regalis (Royal Fern)
Pteridium aquilinum (Bracken Fern)
Asplenium montanum (Mountain Spleenwort)
Athyrium filix-femina var angustum (Northern Lady Fern)
Dryopteris carthusiana (deciduous shield fern)
Actaea pachypoda (White Baneberry)
Aquilegia canadensis (Columbine)
Hepatica acutiloba (Sharp-lobe Hepatica)
Thalictrum thalictroides (Rue Anemone)
Viola conspersa (American Dog Violet)
Viola rostrata (Long-spurred Violet)
Viola sagittata (Arrow-leaved Violet)
Viola sororia (Downy Wood Violet)
Pyrola rotundifolia (Round-leaf Pyrola)
Monotropa uniflora (Indian Pipe)
Lysimachia quadrifolia (Whorled Loosestrife)
Trientalis borealis (Star Flower)
Tiarella cordifolia (Foamflower)
Geum canadensis (White Avens)
Gillenia trifoliata (Bowman's Root)
Waldsteinia fragarioides (Barren Strawberry)
Circaea alpina (Alpine Enchanter's Nightshade)
Epilobium angustifolium (Fireweed)
Comandra umbellata (Bastard Toadflax)
Polygala sanguinea (Purple Milkwort)
Polygala verticillata (Whorled Milkwort)
Geranium maculatum (Wild Geranium)
Apocynum androsaemifolium (Spreading Dogbane)
Melampyrum lineare var americanum (American Cow Wheat)
Veronica officinalis (Common Speedwell)
Galium circaezans (Wild Lcorice)
Mitchella repens (Partridge Berry)
Anaphalis margaritacea (Pearly Everlasting)
Antennaria plantaginifolia (Plantain-leaf Pussytoes)
Aster acuminatus (Mountain Aster)
Aster cordifolius (Blue Wood Aster)
Erechtites hieracifolia (Burnweed)
Solidago bicolor (Silverrod)
Solidago juncea (Early Goldenrod)
Solidao nemoralis (Old Field Goldenrod)
Solidago squarrosa (Stout Goldenrod)
Carex gracillima
Carex hirsutella
Carex scoparia
Carex swanii
Brachyelytrum erectum (Bearded Shorthusk)
Panicum acuminatum (a panic grass)
Panicum commutatum (Variable Panic Grass)
Trillium gradifloram (Large-flowered Trillium)
Trillium undulatum (Painted Trillium)
Corallorrhiza maculata (Spotted Coral-root)
Goodyera pubescens (Downy Rattlesnake Plantain)
Spirathes ochroleuca (Yellow Nodding Lady's Tresses)As noted by W.E. Clyde Todd, one of the earliest commentators on the Swamp (Bier, 2003), the swamp has, or once had, a rough concentric structure in terms of floristics, with Tamarack and Sphagnum mosses dominating the core and this successively surrounded by spruce-Balsam Fir and an outer fringe of Hemlock That Hemlock does not appear in our list of taxa merely illustrates the incompleteness of the compilation, extensive as it is.
According to Rhoads and McKinley (1993) the enveloping regional upland forest here is "Appalachian Oak", or in Braun's (1950) terms, "Oak-Chestnut Forest." That only one species of oak, Northern Red Oak, appears in the compilation, may again illustrate its limitations. However it may also be the case that the canopy here is dominated by this, the farthest north-ranging eastern oak. In Virginia it is practically the only canopy-sized oak above 4000 feet (1200 meters) asl. An example is the forest on Reddish Knob (see our section on this area). However, the list of taxa for the "Dry to Mesic Forests and Openings" contains numerous species, such as Pitch Pine, Black Birch, Downy Serviceberry, Upland Low Blueberry, Mountain Laurel and Bastard Toadflax, that characterize the Oak-Chestnut type forest in general. It should also be noted that, in keeping with its relatively northern position, this forest is also rich in such northern species as Mountain Ash, Early Low Blueberry, Star Flower and Mountain Aster, species usually found at much higher elevations, such as Reddish Knob, or in the coldest valleys, in Virginia.
The generally siliceous character of the country rock in the vicinity of the Swamp leads us to expect dominance by acidiphile floras. This conclusion is generally supported by the derived list of species for the area, which is indeed dominated by acidiphiles, although some calciphiles are also present.
Ricketts Glen
The Ricketts Glen vicinity is an outstanding area of topographic and biologic diversity that lies within the northeastern region of Wisconsinan Glaciation. The southern part of the area is comprised of the steep scarp of the Allegheny Front, which rises a thousand feet (300 meters) above the lowlands to the south. However, much of the area lies on the Allegheny Plateau, which is characterized by low relief and interrupted drainage characteristic of glaciated regions. Rocks of the Plateau, which have the gently-folded to nearly flat-lying character of the Allegheny Plateau, are dominated by the Mississippian Bergoon Sandstone (Berg et al, 1980). However, there are also scattered occurrences of Mississippian Mauch Chunk Formation, which, while mostly grayish-red shale, siltstone and some conglomerate, also includes a Greenbrier Limestone member as well as the Wymps Gap and Deer Valley Limestones. Exposed on the Front mid-scarp is the Mississippian / Devonian Huntley Mountain Formation, which consists of greenish-gray and light olive-gray, flaggy, fine-grained sandstone and a few red-shale interbeds. The base of the scarp is formed by Devonian Catskill Formation of grayish-red sandstone, siltstone and red shale, while the Trimmer's Rock Formation, consisting of olive-gray siltstone and shale, underlies much of the valley. Since this is glaciated terrain, the possible contribution of glacial till to the floral substrate must be considered. For example, given the dominantly siliceous and hence acid character of much of the country rock, an important modifying component from the drift may be material derived from carbonate-rich beds of the Mauch Chunk Formation, which has scattered occurrences to the north in the vicinity and could have been transported southward.
Mesic Forest
Fagus grandifolia (American Beech)
Amelanchier arborea (Downy Serviceberry)
Taxus canadensis (Canada Yew)
Hamamelis virginiana (Witch Hazel)
Ribes cynosbati (Prickly Gooseberry)
Ilex montana (Mountain Holly)
Lonicera canadensis (Fly Honeysuckle)
Viburnum alnifolium (Hobblebush)
Cornus canadensis (Bunchberry)
Lycopodium flabelliforme (Ground Pine)
Lycopodium annotinum (Stiff Clubmoss)
Lycopodium clavatum (Common Clubmoss)
Botrychium dissectum (Cut-leaf Grapefern)
Adiantum pedatum (Maidenhair Fern)
Vittaria appalachiana (Appalachian Shoestring Fern)
Trichomanes intricatum (Weft Fern)
Thelypteris noveboracensis (New York Fern)
Thelypteris phegopteris (Northern Beech Fern)
Camptosorus rhizophyllus (Walking Fern)
Asplenium trichomanes (Maidenhair Spleenwort)
Athyrium filix-femina var. angustum (Northern Lady Fern)
Dropteris goldiana (Goldie's Shield Fern)
Dryopteris disjuncta (Oak Fern)
Polytrichum acrostichoides (Christmas Fern)
Actaea pachypoda (White Baneberry)
Clatonia caroliniana (Carolina Spring Beauty)
Hypericum punctatum (Dotted St. Johnswort)
Viola blanda (Sweet White Violet)
Viola canadensis (Canada Violet)
Viola rotundifolia (Round-leaf Violet)
Dentaria diphylla (Two-leaf Toothwort)
Cardamine pensylvanica (Pennsylvania Bittercress)
*Pyrola secunda (One-sided Wintergreen)
Pyrola rotundifolia (Round-leaf Pyrola)
Pyrola elliptica (Shinleaf)
Trientalis borealis (Star Flower)
Mitella diphylla (Miterwort)
Tiarella cordifolia (Foamflower)
Dalibarda repens (Star Violet)
Fragaria virginiana (Virginia Strawberry)
Circaea alpina (Alpine Enchanter's Nightshade)
Oxalis montana (White Wood Sorrel)
Geranium robertianum (Herb Robert)
Panax quinquefolius (Ginseng)
Hydrophyllum canadense (Broad-leaf Waterleaf)
Hydrophyllum virginianum (Virginia Waterleaf)
Lycopus virginicus (Horehound)
Monarda didyma (Oswego Tea)
Epifagus virginiana (Beechdrops)
Galium triflorum (Sweet-scented Bedstraw)
Aster acuminatus (Mountain Aster)
Aster divaricatus (White Wood aster)
Prenanthes alba (White Lettuce)
Solidago arguta (Cutleaf Goldenrod)
Solidago flexicaulis (Broad-leaf Goldenrod)
Arisaema triphyllum spp triphyllum (Indian Turnip)
Carex baileyi
Carex brunnescens
Carex communis
Carex debilis var rugei
Carex frankii
Carex gracillima
Carex laxiculmis var laxiculmis
Carex leptonervia
Carex oligosperma
Carex pallescens
Carex plantaginea
Carex projecta
Carex scabrata
Brachyelytrum erectum (Bearded Shorthusk)
Glyceria melicaria (Slender Manna-grass)
Poa alsodes (Grove Meadow Grass)
Clintonia borealis (Yellow Clintonia)
Erythronium americanum (Troutlily)
Smilacina racemosa (Plume Lily)
Streptopus amplexifolius (White Twisted-stalk)
Streptopus roseus (Red Twisted-stalk)
Trillium erectum (Wakerobin)
Trillium undulatum (Painted Trillium)
Uvularia sessilifolia (Sessile-leaf Bellflower)
Goodyera pubescens (Downy Rattlesnake Plantain)
Habenaria psycodes var grandiflora (Large Purple Fringed Orchid)
Habenaria orbiculata (Large Round-leaved orchid)
Dry Forests and Openings
Populus grandidentata (Big-leaf Aspen)
Crataegus flabellata (Fan-leaf Hawthorn)
Kalmia latifolia (Mountain Laurel)
Rhododendron nudiflorum (Pinxter Azalea)
Rhododendron roseum (Mountain Azalea)
Vaccinium angustifolium (Early Low Blueberry)
Viola sagittata (Arrow-leaved Violet)
Polygonum cilinode (Mountain Bindweed)
Polgala paucifolia (Gaywings)
Aralia hispida (Bristly Sarsaparilla)
Solanum carolinense (Carolina Horsenettle)
Melampyrum lineare var americana (American Cow Wheat)
Lobelia spicata var spicata (Spiked Lobelia)
Anaphalis margaritacea (Pearly Everlasting)
Cirsium pumilum (Field Thistle)
Solidago bicolor (Silverrod)
Solidago puberula (Downy Goldenrod)
Carex scoparia
Carex virescens
Danthonia compressa (Mountain Oatgrass)
Eragrostis spectabilis (Purple Lovegrass)
Panicm acuminatum (a panic grass)
Corallorhiza maculata (Spotted Coral-root)
Spiranthes lacera var lacera (Ladies' Tresses)
Open Water, Seeps and Wet Meadows
Populus tremuloides (Trembling Aspen)
Alnus rugosa (Speckled Alder)
Hypericum ellipticum (Creeping St. Johns-wort)
Aronia arbutifolia (Red Chokeberry)
Aronia melanocarpa (Black Chokeberry)
Rubus hispidus (Swamp Dewberry)
Ilex verticillata (Winterberry Holly)
Viburnum cassinoides (Wild Raisin)
Viburnum recognitum (Arrowwood Viburnum)
Isoetes muricata (Spiny-spored Quillwort)
Thelypteris palustris (Marsh Fern)
Dryopteris cristata (Crested Shield Fern)
Nuphar lutea (Cowlily)
Nymphaea odorata (Fragrant Water Lily)
Brasenia schreberi (Water Shield)
Caltha palustris (Marsh Marigold)
Stellaria longifolia (Long-leaved Stitchwort)
Viola cucullata (Marsh Blue Violet)
Chrysosplenium americanum (Golden Saxifrage)
Geum rivale (Purple Avens)
Hydrocotyle americana (Water Pennywort)
Menyanthes trifoliata (Buckbean)
Scutellaria epilobiifolia (Marsh Skullcap)
Callitriche heterophylla (Larger Water Starwort)
Utricularia clandestina (a bladderwort)
Utricularia vulgaris (Greater Bladderwort)
Aster prenanthoides (Crooked-stem Aster)
Bidens cernua (Nodding Beggartick)
Cirsium muticum (Swamp Thistle)
Sagittaria graminea var graminea
Potamogeton epihydrus (Floatingleaf Pondweed)
Potamogeton oakesianus (Oakes' Pondweed)
Arisaema triphyllum spp stewardsanii
*Calla palustris (Wild Calla)
Juncus brevicaudatus
Juncus canadensis
Carex canescens var disjuncta
Carex folliculata</p>
Carex gynandra
Carex intumescens
Carex lurida
Carex prasina
Carex stipata var stipata
Carex stricta
Carex utriculata
Cladium mariscoides (Twig Rush)
Scirpus torreyi (Torrey's Bullrush)
Pontederia cordata (Pickerel Weed)
Acid Swamp and Bog
Abies balsamea (Balsam Fir)
Larix laricina (Tamarack)
*Picea mariana (Black Spruce)
Andromeda glaucophylla (Bog Rosemary)
*Chamaedaphne calyculata (Leatherleaf)
Gaultheria hispidula (Creeping Snowberry)
*Ledum groenlandicum (Labrador Tea)
Vaccinium macrocarpon (Large Cranberry)
Vaccinium myrtilloides (Sourtop Blueberry)
Vaccinium oxycoccos (Small Cranberry)
Ribes glandulosum (Skunk Currant)
Amelanchier bartramiana (Oblong-fruited Serviceberry)
Nemopanthus mucronatus (Mountain Holly 2)
Bartonia virginica (Yellow Screwstem)
Gentiana linearis (Narrow-leaf Gentian)
Scheuchzeria palustris (Podgrass)
Carex echinata (Prickly Sedge)
Carex trisperma (Three-seeded Sedge)
*Eriophorum tenellum (Rough Cotton Sedge)
*Eriphorium vaginatum spp spissum (a cotton sedge)
Eriophorum virginicum (Tawny Cotton Sedge)Although not emphasized by Braun (1950), much of the floral diversity of the closed-canopy forest at Ricketts Glen doubtless is a consequence of the differences in elevation and varying slope and aspect in the steep ravines of the Allegheny Front scarp. Braun distinguished the forest types of "flats", along streams from those of the steep slopes of the narrow gorges. It is possible that the relative abundance of such species as Sugar maple and White Ash, as well as those of more southern distribution, as Tuliptree (Liriodendron tulipifera), White Oak (Quercus alba) and the hickories (Carya spp), is in part attributable to a glacial drift substrate enhanced by calcium, magnesium and other nutrients derived from the Mauch Chunk Formation.
Tobyhanna / Bender Swamp
The Tobyhanna / Bender Swamp area is perhaps typical of the glaciated Pocono Plateau lake / wetland complex, a region unique in the Central Appalachians for its diverse northern flora in close association with one more characteristic of the Appalachians. Bedrock in the general area is Upper Devonian Catskill Formation. Dominant is the Duncannon Member, consisting of grayish-red sandstone, with siltstone and claystone in fining upward cycles. Conglomerate occurs at the base of some cycles. Also common is the Poplar Gap Member, which is composed of gray and light-olive-gray sandstone conglomerate with intermittant red beds (Berg et al, 1980). Although these formations are largely covered by glacial till, which may cotain constituents from outside the immediate area, the widespread occurrence of Catskill Formation and other siliceous rocks to the north would seem to indicate that acid soils are to be expected here as well.While its elevation is a little less than 2000 feet (610 m) asl, the generally high water tables, consequent to the interrupted drainage, combined with an unusually cool and moist regional climate, create microclimates in the wetlands that are more characteristic of the Canadian zone.Latham et al (1996) have pointed out that the Pocono Plateau coincides with the area of the coolest mean daily maximum summer temperatures in Pennsylvania, while a climate station at Long Pond had, for the period of 1961-1990, the highest mean annual precipitation (129.2 cm) of all 161 stations in the State (Owenby and edzell, 1992). This relation is similar to that which was previously found in the vicinity of boreal wetlands on the Warren / Erie County line However on the warmer slopes of modest local elevations the forest in the Pocono region, while mostly northern hardwood, also contains an admixture of species characteristic of the southern Appalachians.
The area of interest, approximately 15 square miles in size, is located on and below the Monroe / Wayne County line, east and southeast of Gouldsboro Lake, extending to the east side of Bender Swamp and includes such uplands as Powder Smoke Ridge.
As in our other lists, an asterisk indicates that a taxon does not range south to Virginia or West Virginia.
Mesic Forest
Tsuga canadensis (Canada Hemlock)
Ulmus rubra (Slippery Elm)
Fagus grandifolia (American Beech)
Prunus serotina (Black Cherry)
Robinia pseudoacacia (Black Locust)
Acer negundo (Boxelder)
Acer rubrum var rubrum (Red Maple)
Acer rubrum var trilobum (Red Maple)
Acer saccharum var saccharum (Sugar Maple)
Fraxinus americana (White Ash)
Carpinus caroliniana (Muscletree)
Amelanchier arborea (Downy Serviceberry)
Amelanchier laevis (Smooth Serviceberry)
Cornus alternifolia (Alternate-leaf Dogwood)
Acer pensylvanicum (Striped Maple)
Acer spicatum (Mountain Maple)
Rosa carolina (Carolina Rose)
Rubus canadensis (Thornless Blackberry)
Ilex montana var beadlei (Mountain Holly)
Ilex montana (Mountain Holly)
Lonicera canadensis (Fly Honeysuckle)
Sambucus pubens (Red Elderberry)
Viburnum acerifolium (Maple-leaf Viburnum)
Viburnum alnifolium (Hobblebush)
Cornus canadensis (Bunchberry)
Gaultheria procumbens (Teaberry)
Rhus radicans (Poison Ivy)
Vitis labrusca (Fox Grape)
Smilax hispida (Hispid Greenbrier)
Smilax rotundifolia (Common Greenbrier)
Lycopodium flabelliforme (Ground Pine)
Lycopodium lucidulum (Shining Clubmoss)
Lycopodium annotinum (Stiff Clubmoss)
Lycopodium obscurum var dendroideum (Tree Clubmoss)
Lycopodium obscurum (Tree Clubmoss)
Botrychium dissectum (Cut-leaf Grape Fern)
Botrychium multifidum (Leathery Grape Fern)
Osmunda claytoniana (Interrupted Fern)
Lygodium palmatum (Climbing Fern)
Dennstaedtia punctilobula (Hay-scented Fern)
Dryopteris carthusiana (deciduous Spinulose Shield Fern)
Dryopteris intermedia (Intermediate Shield Fern)
Thelypteris novaeboracencis (New York Fern)
Thelypteris phegopteris (Northern Beech Fern)
Actaea pachypoda (White Baneberry)
Aquilegia canadensis (Columbine)
Ranunculus abortivus (Kidney-leaf Crowfoot)
Caulophyllum thalictroides (Blue Cohosh)
Viola blanda (Sweet White Violet)
Viola rotundifolia (Round-leaf Violet)
Dentaria diphylla (Two-leaf Toothwort)
Chimaphila maculata (Spotted Wintergreen)
Pyrola rotundifolia (Round-leaf Pyrola)
Monotropa uniflora (Indian Pipe)
Trientalis borealis (Star Flower)
Tiarella cordifolia (Foamflower)
Agrimonia striata (Woodland Agrimony)
Dalibarda repens (Star Violet)
Fragaria virginica (Virginia Strawberry)
Oxalis montana (White Wood Sorrel)
Geranium robertianum (Herb Robert)
Aralia nudicaulis (Wild Sarsaparilla)
Aralia racemosa (American Spikenard)
Osmorhiza claytoni (Hairy Sweet Cicely)
Apocynum androsaemifolium (Spreading Dogbane)
Asclepias exaltata (Poke Milkweed)
Cuscuta granovii var granovii (Gronovius Dodder)
Collinsonia canadensis (Horse Balm)
Monarda didyma (Oswego Tea)
Prunella vulgaris var lanceolata (American Self-heal)
Epifagus virginiana (Beech Drops)
Galium triflorum (Sweet-scented Bedstraw)
Mitchella repens (Partridge Berry)
Aster acuminatus (Mountain Aster)
Aster divaricatus (White Wood Aster)
Aster macrophyllus (Big-leaf Aster)
Aster patens (Late Purple Aster)
Lactuca biennis (Tall Blue Lettuce)
Senecio obovatus (Round-leaf Ragwort)
Arisaema triphyllum spp triphyllum (Indian Turnip)
Luzula multiflora (Heath Woodrush)
Carex annectens
Carex appalachica
Carex arctata
Carex brunnescens
Carex debilis var rudgei
Carex deweyana var deweyana
Carex novae-angliae
Carex pallescens
Carex projecta
Agrostis perennans (Autumn Bent Grass)
Brachyelytrum erectum (Bearded Shorthusk)
Elymus trachycaulis (Slender Wheat Grass)
Festuca obtusa (Nodding Fescue)
Glyceria melicaria (Slender Mannagrass)
Muhlenbergia glomerata
Panicum latifolium (Broad-leaf Witchgrass)
Poa saltuensis (Drooping Bluegrass)
Clintonia borealis (Yellow Clintonia)
Lilium canadense spp canadense (Canada Lily)
Maianthemum canadense (Canada Mayflower)
Medeola virginiana (Indian Cucumber-root)
Polygonatum pubescens (Downy Many Knees)
Smilacina racemosa (Plume Lily)
Sreptopus roseus var perspectus (Red Twisted-stalk)
Trillium erectum var erectum (Wakerobin)
Trillium undulatum (Painted Trillium)
Corallorhiza odontorhiza (Late Coral-root)
Liparis lilifolia (Large Twayblade)
Malaxis unifolia (Green Adder's Mouth)
Spiranthes lacera var lacera (Ladies' Tresses)
Spiranthes ochroleuca (Yellow Nodding Ladies' Tresses)
Dry Forest and Openings
Pinus rigida (Pitch Pine)
Sassafras albidum (Sassafras)
Betula lenta (Black Birch)
Betula populifolia (Gray Birch)
Sorbus americana (Mountain Ash)
Kalmia latifolia (Mountain Laurel)
Vaccinium angustifolium (Early Low Blueberry)
Vaccinium pallidum (Upland Low Blueberry)
Rhus copallina (Winged Sumac)
Rhus glabra (Smooth Sumac)
Rhus typhina (Staghorn Sumac)
Diervilla lonicera (Bush Honeysuckle)
Rubus strigosus (Red Raspberry)
Aralia hispida (Bristly Sarsaparilla)
Lycopodium clavatum (Common Clubmoss)
Lycopodium tristachyum
Pteridium aqilinum (Bracken Fern)
Pyrola virens (Greenish-flowered Wintergreen)
Lechea pulchella (Leggett's Pinweed)
Lepidium virginianum (Wild Pepper Grass)
Lupinus perennis (Lupine)
Epilobium angustifolium (Fireweed)
Oenothera perennis (Small Sundrops)
Comandra umbellata (Bastard Toadflax)
Asclepias syriaca (Common Milkweed)
Melampyrum lineare var americanum (American Cow Wheat)
Lobelia inflata (Indian Tobacco)
Lobelia spicata var spicata (Spiked Lobelia)
Ambrosia artemisiifolia (Common Ragweed)
Anaphalis margaritacea (Pearly Everlasting)
Antennaria parlinii spp fallax
Aster undulatus (Wavy-leaf Aster)
Cirsium pumilum (Pasture Thistle)
Erectites hieracifolia (Burnweed)
Erigeron strigosus var strigosus
Helianthus divaricatus (Woodland Sunflower)
Hieracium paniculatum (Panicled Hawkweed)
Hieracium scabratum
Hieracium venosum (Rattlesnake Weed)
Lactuca canadensis var canadensis
Prenanthes trifoliata
Solidago bicolor (Silverrod)
Solidago juncea (Early Goldenrod)
Solidago nemoralis (Old Field Goldenrod)
Solidago puberula (Downy Goldenrod)
Juncus tenuis (Trail Rush)
Carex argyrantha
Carex communis
Carex hirsutella
Carex normalis
Carex swanii
Cyperus lupulinus
Danthonia compressa (Mountain Oatgrass)
Danthonia spicata (Poverty Oatgrass)
Eragrostis pectinacea
Panicum acuminatum
Panicum depauperatum
Panicum meridonale
Panicum philadelphicum
Lilium philadelphicum (Wood Lily)
Sisyrinchium mucronatum (Michaux Blue-eyed Grass)
Corallorhiza maculata (Spotted Coral-root)
Cypripedium acaule (Pink Ladyslipper)
Malaxis bayordii (Adder's Mouth)
Open Waters, Seeps and Wet Meadows
Populus tremuloides (Trembling Asten)
Alnus rugosa (Speckled Alder)
*Salix bebbiana (Beb Willow)
Salix discolor (Glaucus Willow)
*Salix cordata (Heart-leaf Willow)
Salix lucida (Shining Willow)
Salix sericea (Silky Willow)
Aronia arbutifolia (Red Chokeberry)
Aronia melanocarpa (Black Chokeberry)
Aronia prunifolia (Purple Chokeberry)
Rubus hispidus (Swamp Dewberry)
Rubus pubescens (Dwarf Raspberry)
Rubus setosus (Bog Blackberry)
Spiraea latifolia (Meadowsweet)
Spiraea tomentosa (Hardhack)
Ilex laevigata (Smooth Winterberry)
Cephalanthus occidentalis (Buttonbush)
Sambucus canadensis (Black Elderberry)
Viburnum cassinoides (Wild Raisin)
Viburnum recognitum (Northern Arrowwood)
Ribes glanulosum (Skunk Currant)
Lycopodium annotinum (Stiff Clubmoss)
*Isoetes muricata (a quillwort)
Equisetum arvense (Field Horsetail)
Equisetum sylvaticum (Woodland Horsetail)
Osmunda cinnamomea (Cinnamon Fern)
Osmunda regalis (Royal Fern)
Thelypteris palustris (Marsh Fern)
Athyrium filix-femina var angustum (Northern Lady Fern)
Dryopteris cristata (Crested Shield Fern)
Onoclea sensibilis (Sensitive Fern)
Woodwardia virginica (Virginia Chain Fern)
Caltha palustris var palustris (Marsh Marigold)
Caltha palustris var flabellifolia (Marsh Marigold)
Coptis groenlandica (Goldthread)
Thalictrum pubescens (Tall Meadowrue)
Silene alba (White Campion)
Stellaria longifolia (Long-leaved Stitchwort)
Polygonum sagittatum (Arrowleaf Tearthumb)
Hypericum canadense (Canada St. Johnswort)
Hypericum ellipticum (Creeping St. Johnswort)
Triadenum fraseri (Bog St. Johnswort)
Viola cucullata (Marsh Blue Violet)
Rorippa paustris spp palustris
Lysimachia ciliata (Purple-fringed Loosestrife)
Lysimachia terrestris (Swamp Candles)
Chrysosplenium americanum (Golden Saxifrage)
Sanguisorba canadensis (Canadian Burnet)
Myriophyllum humile (Low Water Milfoil)
Decodon verticillatus (Water Loosestrife)
Epilobium ciliatum (Hairy Willowherb)
Epilobium coloratum (Purple-leaved Willowherb)
Ludwigia paustris (Marsh Purslane)
Impatiens capensis (Spotted Jewelweed)
Cicuta bulbifera (Water Hemlock)
Cicuta maculata (Spotted Cowbane)
Sium suave (Water Parsnip)
Gentiana linearis (Narrow-leaved Gentian)
Gentiana crinita (Fringed Gentian)
Myosotis laxa (Wild Forget- me-not)
Scutellaria lateriflora (Mad-dog Skullcap)
Callitriche lateriflora (Larger Water Starwort)
Callitriche palustris (Common Water Starwort)
Chelone glabra (Turtlehead)
Veronica scutellata (Mash Speedwell)
Utricularia cornuta (Horned Bladderwort)
Utricularia macrorhiza (Common Bladderwort)
Lobelia cardinalis (Cardinal Flower)
Galium asprellum (Rough Bedstraw)
Aster simplex var simplex (Panicled Aster)
Aster umbellatus (Flat-top White Aster)
Bidens cernua (Nodding Beggar-tick)
Bidens connata
Eupatorium fistulosum (Hollow Joe-Pye Weed)
Eupatorium perfoliatum (Boneset)
Euthamia graminifolia var nuttallii (Grass-leaved Goldenrod)
Gnaphalium uliginosum (Low Cudweed)
Lactuca canadensis var longifolia
Senecio aureus (Golden Ragwort)
Solidago rugosa var rugosa (Wrinkle-leaf Goldenrod)
Sagittaria latifolia (Arrowhead)
Potamogeton epihydrus
Potamogeton pusillus
Arisaema triphyllum spp stewardsonii (Indian Turnip)
*Calla palustris (Wild Calla)
Orontium aquaticum (Golden Club)
Spirodella polyrhiza (Greater Duckweed)
Eriocaulon aquaticum (White Buttons)
Juncus brevicaudatus
Juncus effusus var pylaei
Juncus effusus var solutus ???
Juncus marginatus var marginatus
Juncus pelocarpus
Juncus subcaudatus
Carex atlanticus spp capillacea
Carex baiylei
Carex canescens var canescens
Carex canescens var disjuncta
Carex folliculata
Carex gynandra
Carex intumescens
Carex lurida
Carex scabrata
Carex scoparia
Carex stricta
Carex utriculata
Carex vulpinoidea var vulpinoidea
Dulichium arundinaceum (Three-way Sedge)
Eleocharis obtusa var obtusa
Eleocharis olivacea
Eleocharis tenuis var tenuis
Eriophorum virginicum (Tawny Cottonsedge)
Scirpus atrovirens
Scirpus validus
Calamagrostis canadensis (Blue Joint Grass)
Calamagrostis cinnoides
Elymus canadensis var canadensis
Glyceria canadensis (Rattlesnake Grass)
Glyceria grandis (American Mannagrass)
Glyceria striata (Fowl Mannagrass)
Leerzia oryzoides (Rice Cutgrass)
Panicum clandestinum (Deer-tongue Grass)
Panicum virgatum (Switch Grass)
Poa palustris (Fowl Bluegrass)
Sparganium americanum (Bur-reed)
Typha latifolia (Common Cattail)
Pontederia cordata (Pickerel Weed)
Iris versicolor (Blue Flag)
Habenaria clavellata (Small Green Wood Orchid)
Acid Swamp and Bog
Abies balsamea (Balsam Fir)
Larix laricina (Tamarack)
*Picea mariana (Black Spruce)
Picea rubens (Red Spruce)
Andromeda glaucophylla (Bog Rosemary)
*Chamaedaphne calyculata (Leatherleaf)
Gaultheria hispidula (Creeping Snowberry)
*Kalmia angustifolia (Sheep Laurel)
*Kalmia polifolia (Bog Laurel)
*Ledum groenladicum (Labrador Tea)
Lyonia ligustrina (Maleberry)
*Rhododendron canadense (Rhodora)
Rhododendron viscosum (Swamp Azalea)
Vaccinium corymbosum (Highbush Blueberry)
Vaccinium macrocarpon (Large Cranberry)
Vaccinium myrtilloides (Sourtop Blueberry)
Vaccinium oxycoccos (Small Cranberry)
Amelanchier bartramiana (Oblong-fruited Serviceberry)
Geum laciniatum var laciniatum (Rough Avens)
Arceuthobium pusillum (Dwarf Mistletoe) (chiefly on Black Spruce)
Scheuchzeria palustris (Podgrass)
Carex echinata (Prickly Sedge)
Carex leptalea
*Carex limosa
Carex oligosperma
*Carex paupercula
Carex trisperma
*Eriophorum vaginatum spp spissum (Sheathed Cottonsedge)
Rhynchospora alba (White Beakrush)
*Smilacina trifolia (Three-leaved Plume Lily)
Corallorhiza trifida (Early Coralroot)
Liparis loesellii (Bog Twayblade)
Habenaria blephariglottis (White Fringed Orchid)
Pogonia ophioglossoides (Rose Pogonia)Pocono Till Barrens
The Mesic Till Barrens (Latham et al, 1996; Eberhardt and Latham, 2000; Latham, 2003) occupy part of a 11x30 km area in the southern part of the Pocono Plateau, with a mean elevation of 550 meters (1790 feet) asl. The bedrock geology consists of the same Upper Devonian Formation members which are described for the Tobyhanna / Bender Swamp area (Berg et al, 1980). It is overlain by dominantly Illinoian glacial till and minor till of Wisconsinan age. The area of Mesic Till Barrens is bounded on the southeast by the Pocono Plateau escarpment, which is occupied by dry till barrens. The Mesic till barrens consist of three major types: Heath Barrens, Rhodora (Rhododendron canadense) Barrens and Scrub Oak (Quercus ilicifolia) Barrens.
According to Latham et al (1996) and Latham (2003), the following species, in order of life form, characterize the mesic till barrens.
Vascular Plants
Larix laricina (Tamarack) - nearly absent
Picea rubens (Red Spruce) - primarily as seedlings and saplings
Pinus rigida (Pitch Pine) - one of the most common species
Pinus strobus (White Pine)
Tsuga canadensis (Canada Hemlock) - nearly absent
Sassafras albidum (Sassafras) - primarily as seedlings and saplings
Quercus alba (White Oak) - nearly absent
Quercus coccinea (Scarlet Oak) - nearly absent
Quercus palustris (Pin Oak)
Betula populifolia (Gray Birch)
Populus tremuloides (Trembling Aspen) - primarily as seedlings and saplings
Amelanchier arborea (Downy Serviceberry)
Amelanchier laevis (Smooth Serviceberry)
Prunus serotina (Black Cherry) - nearly absent
Prunus pensylvanica (Fire Cherry) - nearly absent
Nyssa sylvatica (Black Gum) - nearly absent
Acer rubrum (Red Maple) - one of the most common species
Hamamelis virginiana (Witch Hazel)
Comptonia peregrina (Sweet Fern)
Quercus ilicifolia (Bear or Scrub Oak) -one of the most common species
Salix humilis (Upland Willow)
*Chamaedaphne calyculata (Leatherleaf)
Epigaea repens (Trailing Arbutus)
Caultheria procumbens (Teaberry) - one of the most common species
Gaylussacia baccata (Black Huckleberry)
Gaylussacia frondosa (Dangleberry)
Kalmia angustifolia (Sheep Laurel) - one of the most common species
Lyonia ligustrina (Maleberry)
*Rhododendron canadense (Rhodora) - one of the most common species
Vaccinium angustifolium (Early Low Blueberry) - one of the most common species
Vaccinium corymbosum (Highbush Blueberry) - primarily as seedlings and immature shrubs
Vaccinium myrtilloides (Saurtop Blueberry)
Vaccinium pallidum (Upland Low Blueberry)
Vaccinium stamoneum (Deerberry)
Amelanchier sanguinea (Red-twigged Serviceberry)
Amelanchier stolonifera (Running Serviceberry)
Aronia melanocarpa (Black Chokeberry) - one of the most common species
Rubus hispidus (Swamp Dewberry) - one of the most common species
Spiraea alba (Pipestem)
Spiraea tomentosa (Hardhack)
Cornus canadensis (Bunchberry)
Ilex montana (Mountain Holly) - nearly absent
Viburnum cassinoides (Wild Raisin) - one of the most common species
Smilax rotundifolia (Common Greenbrier)
Lycopodium flabelliforme (Ground Pine)
Lycopodium hickey (Hickey's Clubmoss)
Lycopodium obscurum (Tree Clubmoss)
Osmunda cinnamomea (Cinnamon Fern)
Osmunda claytoniana (Interrupted Fern)
Dennstaedtia punctilobula (Hay-scented Fern)
Pteridium aquilinum (Bracken Fern) - one of the most common species
Lygodium palmatum (American Climbing Fern)
Coptis groenlandica (Goldthread)
Polygala paucifolia (Gaywings)
Monotropa uniflora (Indian Pipe)
Lysimachia quadrifolia (Whorled Loosestrife)
Trientalis borealis (Star Flower)
Comandra umbellata (Bastard Toadflax)
Aralia hispida (Bristly Sarsaparilla)
Aralia nudicaulis (Wild Sarsaparilla)
Panax trifolius (Dwarf Ginseng)
Bartonia virginica (Yellow Screwstem)
Gentiana linearis (Narrow-leaf Gentian)
Melampyrum lineare (Cow Wheat)
Mitchella repens (Partridge Berry)
Aster umbellatus (Flat-top White Aster)
Erechtites hieracifolia (Burnweed)
Prenanthes trifoliata (Gall-of-the-Earth)
Solidago puberula (Downy Goldenrod)
Juncus filiformis (Thread Rush)
Carex pensylvanica (Pennsylvania Sedge) - one of the most common species
Carex polymorpha (Variable Sedge)
Carex stricta
Carex vestita
Eleocharis tenuis (Slender Spikerush)
Brachyelytrum erectum (Bearded Shorthusk)
Calamagrostis canadensis (Blue Joint Grass)
Calamagrostis cinnoides
Danthonia spicata (Poverty Oat Grass)
Oryzopsis racemosa (Mountain Ricegrass) - one of the most common species
Panicum boreale (Northern Panic Grass)
Panicum meridionale (Matting Witchgrass)
Amianthium muscaetoxicum (Fly Poison)
Lilium philadelphicum (Wood Lily)
Maianthemum canadense (Canada Mayflower)
Medeola virginiana (Indian Cucumberroot)
Trillium undulatum (Painted Trillium)
Uvularia sessilifolia (Sessile-leaved Bellwort)
Smilax herbacea (Carrion Flower)
Cipripedium acaule (Pink ladyslipper)
Habenaria blephariglottis (White Fringed Orchid)
Mosses
Aulacomnium androgynum
Pohlia cf. nutans
Dicranum montanum
Dicranum scoparium
Callicladium haldanianum
Hypnum imponens
Leucobryum glaucum
Polytrichum commune - one of the most common species
Sphagnum capillifolium
Sphagnum magellanicum
Sphagnum palustre
Based on experience with a variety of Central Appalachian habitats, it seems likely that this list represents only a fraction of the bryophye community of these barrens.
According to Latham et al (1996) and Latham (2003) the principal disturbance form which has affected the barrens in the past is fire, and the central problem is the existence of these till barrens on soils and in a general environment that does not appear to differ significantly from those which characterize the regional northern hardwood closed canopy forest, except for the history of fire in the Barrens. The sharp boundary between shrubland and forest corresponds to no detectable discontinuity or gradient in soil characteristics except in the organic layer, which, in the view of Latham, is developed mainly by the plants themselves together with microbes, animals and fire. Curiously, in samples which show a barely detectable difference, the shrubland soils actually have slightly higher concentrations of nutrients than do the forest soils (Wibiralske, 2002) Another unusual characteristic that distinguishes the Mesic Till Barrens from other barrens-which generally occur on dry soils- is the coexistence of speceies characteristic of both wet and dry habitats. Thus the moisture-demanding Maleberry and the dry-soil Upland Low Blueberry both appear in this community. However, it may be that this apparent anomaly can be explained by differences in microtopography. Thus Early Low Blueberry, a species normally of dry sites, also occurs in bogs (Hunsucker et al, 1995), at least in West Virginia. However, in the latter case it is always found on hummocks. Also a number of other species in the list, such as Teaberry and Black Huckleberry, have such broad stability fields that both very dry and wet, but always acidic, habitats are included. A notable feature of both the Mesic Till Barrens and the adjacent forest is the presence at times of unusually high water tables. This is particularly true of those of Rhodora type barrens and Hemlock-Spruce Forest, which over 14 months of 1993 and 1994 had water tables at less than a meter in depth for more than 60 percent of the time (Latham et al, 1996). The Rhodora Type Barrens in fact appears to be characterized by somewhat moister soils than the other types, while the Scrub Oak Type appears to have the dryest soils. Also, when water content of Barrens and forest soils as groups, and those developed on Illinoian Drift and Devonian bedrock were separately compared (Eberhardt and Latham, 2000), very little difference was found in either case.
. Latham (2003) provided an excellent summary of the complex of biotic factors which interact among themselves and with fire, "frost pockets" and other physical factors to create positive feedbacks that sustain the Barrens. The following quote from Latham illustrates the point:
"Each positive feedback has two components: an environmental change brought about by plants and tolerance of the change by those same plants. The dominant plants of mesic heathlands acidify the soil, and they are highly tolerant of soil acidity (Read, 1984). They produce recalcitrant litter, which slows nitrogen and phosphorus mineralization by soil microbes (Grubb et al, 1969; Damman, 1971; Northup et al, 1995, 1998), but they also join with ericoid mycorrhizal fungi, which decompose and take up organically bound nitrogen and phosphorus before they can be mineralized by soil microbes and made suitable to plants with other types of micorrhizal relationships (Read, 1983; Dighton and Coleman, 1992; Leake, 1992). Some shrubland plants are allelopathic, tolerant of their own toxicity and any induced effects on soil microbial communities and nutrient cycling (Read,1984; Mallik, 1995; Inderjit and Weiner, 2001). The resulting positive feedbacks can lead to species assemblages that often superficially resemble early successional stages but persist for a long time by resisting invasion (Lacock,1991; Wilson and Agnew, 1992; Northup et al, 1998).True early successional plants are intolerant of the environmental changes they and other plants produce, especially shade."
Reflecting the above quotation, one of the most common heaths in these barrens is Sheep Laurel, which is known as a strong inhibitor of tree regeneration in dense unshaded stands (Mallik,1993, 1995, 2001).
The shrubs of Mesic Till Barrens produce an abundance of dead dry vegetation rich in flammable substances such as resins. However these same plants also have deeply buried stems and stolons that are insolated from fires. Thus, when this heavy and flammable fuel load ignites, an intense fire results, that, while readily destroying most forest tree seedlings and saplings, only consumes the above-ground barren's shrubs, allowing the latter to resprout in vigorous form. As in the case of toxic substance effects, there is positive feedback as fire produces vegetation of a type that promotes more fire. and hence perpetuation of this vegetation type.
Latham et al (1996) regarded Scrub Oak as possibly the principal fire carrier in the Pocono till barrens system. This species and other highly flammable but fire-tolerant shrubs may originally have established a foothold along the Plateau's southern rim, where sandy soils were derived from sandstones and conglomerates and kept shallow by wind erosion Fires ignited there by lightning strikes could then have spread into the richer soil area of the mesic till barrens during drought periods, killing forest trees and activating the feedback mechanism that was subsequently also in part sustained by Native American and Euro-american-set fires (Latham et al, 1996).
Following Wilson and Agnew (1992), Latham et al (1996) hypothesized that the Pocono till barrens rerpresent an alternative stable community state to the more common forest vegetation of the region.
This model appears reasonable in terms of energetics, which at very least provides an analog. In chemical systems energy (potential?, free?) sufaces at the junction of two adjacent stable (alternative!) states are warped upward in a barrier that limits passage from one state to the other. Energy required to surmount this barrier is the energy of activation, and it is a measure of the difficulty of a system passing from one state to the other. Thus a system in the least stable state (with the highest energy surface) can trasform to the more stable state (with a lower energy surface) in a given time only if enough kinetc energy is available or it is not too difficult (entropy factor). Thus, while the regional northern hardwood forest may be more stable than the mesic till barrens, the presence of the biological and fire feedback mecanisms may present an unsurmountable barrier, at least in the short term.
Central Pennsylvania - General Characteristics
Here we explore a region that incorporates features of previously treated Allegheny Plateau as well as the Ridge and Valley Province. While this region of central Pennsylvania is also unglaciated and includes many communities that are common in Virginia and West Virginia, there are also some areas, like Bear Meadows, that are unique in the Ridge and Valley Province. Also seen here is the northward decrease in mean temperatures at a given elevation and the effect of this on the floras. Our focus will be on Centre and adjacent counties, and while this area incorporates a part of the Allegheny Plateau and the Allegheny Front, our greatest interest is in the adjacent Ridge and Valley Province. The Centre County region is characteristic of the Ridge and Valley Province, with long linear as well as complexly folded ridges dominated by highly erosion-resistant sandstones, conglomerates and quartzites such as the Silurian Tuscarora Formation, and these alternate with valleys consisting of much less resistant shales and limestones. Typical of the long linear ridges is Bald Eagle Ridge, while the complexly-folded ridge topography is well represented by the Seven Mountains area, which includes the classic Bear Meadows Natural Area. Developed on Ordovician Juniata siltstones and sandstones, the Bear Meadows acidic bog and swamp forms the headwaters of Sinking Creek at an elevation of 1820 feet (560 m) asl. Rising some 300 feet (100 m) above Bear Meadows, immeditely to the southwest, and partially enclosing it, is Greenlee Mountain, which is formed of highly resistant Tuscarora qurtzite, and is the site of the Big Flat Laurel Natural Area. In terms of vegetation this elevated area is dominated by stunted Chestnut Oak-heath woodland and Scrub Oak (Quercus ilicifolia) shrubland. Other trees are Black Gum and Sassafras, while Mountain Laurel, Black Huckleberry and Early Low Blueberry are the dominant shrubs. Except for the prominence of this northern type blueberry, this woody flora resembles closely that which characterizes similar bedrock and topography southward to southwestern Virginia. However, in Virginia Early Low Blueberry is likely to be restricted to elevations above 3000 feet. Additionally, the low relief and thin soil over rock on Big Flat Laurel favor the accumulation of moisture in depressions and the existence of a patchwork of small temporary wetlands. Black Gum is said to thrive in these depressions (WPC, 2002).
Down-stream from Bear Meadows the Sinking Creek Valley occupies eroded anticlines and synclines and is floored by successively older Ordovician rocks. Initially porous Juniata sandstones overlying shale-rich and somewhat calcareous Reedsville Formation creates mesic forest habitat rich in Sugar Maple and American Basswood. Farther down-stream Gregg Township is the site of the Sinking Creek Prairie, developed on limestone, and which contains a number of rare and characteristic species, some of which are disjunct from the midwest. Included are Side-oat gramma (Bouteloua curtipendula), Grooved Yellow Flax (Linum sulcatum), Long-fruited Anemone (Anemone cylindrica), Hard-leaved Goldenrod (Solidago rigida), Tufted Buttercup (Ranunculus fascicularis), False Gromwell (Onosmodium molle var hispidissimum) and Wild Chess (Bromus kalmii). Other occurrences of these communities have been discussed by Laughlin and Uhl (2003). It is interesting to compare the Pennsylvania calcareous floras with those of southwestern Virginia (Ludwig, 1999).
Bear Meadows Flora
Adjacent Upland Forest and Openings
Pinus rigida (Pitch Pine)
Pinus strobus (White Pine)
Magnolia acuminata (Cucumbertree)
Sassafras albidum (Sassafras)
Betula lenta (Black Birch)
Betula papyrifera (White Birch)
Tilia americana (American Basswood)
Populus tremuloides (Trembling Aspen)
Amelanchier arborea (Downy Serviceberry)
Sorbus americana (Mountain Ash)
Nyssa sylvatica (Black Gum)
Acer pensylvanicum (Striped Maple)
Corylus cornuta (Beaked Hazelnut)
Gaylussacia baccata (Black Huckleberry)
Rhododendron nudiflorum (Pinxter Azalea)
Vaccinium angustifolium (Early Low Blueberry)
Vaccinium pallidum (Upland Low Blueberry)
Vaccinium stamineum (Deerberry)
Cornus canadensis (Bunchberry)
Parthenocissus quinquefolia (Virginia Creeper)
Vitis aestivalis (Summer Grape)
Rhus typhina (Staghorn Sumac)
Lycopodium flabelliforme (Ground Pine)
Lycopodium annotinum (Stiff Clubmoss)
Lycopodium obscurum var dendroicum (Tree Clubmoss)
Lycopodium obscurum (Tree Clubmoss)
Osmunda claytoniana (Interrupted Fern)
Pteridium aquilinum (Bracken Fern)
Thelypteris noveboracensis (New York Fern)
Dryopteris carthusiana (deciduous spinulose shield fern)
Actaea pachypoda (White Baneberry)
Ranunculus recurvatus (Hooked Crowfoot)
Thalictrum thalictroides (Rue Anemone)
Viola lanceolata (Lance-leaved Violet)
Viola pubescens (Downy Yellow Violet)
Viola fimbriatula (Ovate-leaved Violet)
Viola sororia (Blue Wood Violet)
Monotropa uniflora (Indian Pipe)
Lysimachia quadrifolia (Whorled Loosestrife)
Waldsteinia fragarioides (Barren Strawberry)
Lespedeza hirta (Hairy Bushclover)
Circaea alpina (Alpine Enchanter's Nightshade)
Epilobium angustifolium (Fireweed)
Linum virginianum (Virginia Yellow Flax)
Polygala paucifolia (Gay Wings)
Polygala senega var senega (Seneca Snakeroot)
Angelica venenosa (Hairy Angelica)
Scutellarin integrifolia (Large-flowered Skullcap)
Gratiola neglecta (Clammy Hedge-hyssop)
Melampyrum lineare var americaum (American Cow Wheat)
Lobelia inflata (Indian Tobacco)
Anaphalis margaritacea (Pearly Everlasting)
Aster acuminatus (Mountain Aster)
Eupatorium rugosum (White Snakeroot)
Gnaphallium obtusifolium (Cudweed)
Solidago squarrosa (Squarrose Goldenrod)
Arisaema triphyllum spp triphyllum (Indian Turnip)
Carex debilis var pubera
Carex debilis var rudgei
Carex radiata
Carex rosea
Agrostis perennans (Autumn Bent Grass)
Danthonia compressa (Mountain Oat Grass)
Oryzopsis asperifolia (Mountain Ricegrass)
Oryzopsis racemosa (Mountain Ricegrass)
Panicum acuminatum (Panic Grass)
Panicum dichotomum (Cypress Witchgrass)
Panicum latifolium (Broad-leaf Witchgrass)
Clintonia borealis (Yellow Clintonia)
Lilium philadelphicum (Wood Lily)
Maianthemum canadense (Canada Mayflower)
Medeola viginiana (Indian Cucumberroot)
Trillium undulatum (Painted Trillium)
Smilax herbacea (Carrion Flower)
Cypripedium acaule (Pink Ladyslipper)
Goodyera repens (Dwarf Rattlesnake Plantain)
Isotera verticillata (Whorled Pogonia)
Bear Meadows Wetland
Abies balsamea (Balsam Fir)
Larix laricina (Tamarack)
*Picea mariana (Black Spruce)
Picea rubens (Red Spruce)
Betula alleghaniensis (Yellow Birch)
Acer rubrum var rubrum (Red Maple)
Alnus rugosa (Speckled Alder)
*Chamaedaphne calyculata (Leatherleaf)
Gaultheria procumbens (Teaberry)
Lyonia ligustrina (Maleberry)
Rhododendron maximum (Great Rhododendron)
Vaccinium corymbosum (High-bush Blueberry)
Vaccinium macrocarpon (Large Cranberry)
Vaccinium myrtilloides (Sour-top Blueberry)
Vaccinium oxycoccos (Small Cranberry)
Ribes glandulosum (Skunk Currant)
Aronia arbutifolia (Red Chokeberry)
Aronia melanocarpa (Black Chokeberry)
Aronia prunifolia (Purple Chokeberry)
Rosa palustris (Swamp Rose)
Rubus hispidus (Swamp Dewberry)
Spiraea latifolia (Meadow-sweet)
Ilex verticillata (Winterberry Holly)
Nemopanthus mucronatus (Mountain Holly 2)
Cephalanthus occidentalis (Buttonbush)
Viburnum cassinoides (Wild Raisin)
Viburnum recognitum (Northern Arrow-wood)
Osmunda cinnamomea (Cinnamon Fern)
Thelypteris palustris (Marsh Fern)
Thelypteris simulata (Bog Fern)
Dryopteris cristata (Crested Shield Fern)
Onoclea sensibilis (Sensitive Fern)
Caltha palustris (Marsh Marigold)
Coptis groenlandica (Goldthread)
Hypericum boreale (Northern St. John's-wort)
Hypericum mutilum (Dwarf St. John's-wort)
Triadenum fraseri (Marsh St. John's-wort)
Drosera rotundifolia (Round-leaf Sundew)
Lysimachia terrestris (Swamp Candles)
Impatiens capensis (Spotted Jewelweed)
Bartonia virginica (Yellow Screwstem)
Verbena hastata (Blue Vervain)
Lycopus uniflorus (Northern Bugleweed)
Lycopus virginicus (Bugleweed)
Galium tinctorium (Clayton's Bedstraw)
Aster puniceus (Purple-stem Aster)
Aster umbellatus (Flattop White Aster)
Rudbeckia laciniata (Cut-leaved Coneflower)
Solidago rugosa var rugosa (Wrinkle-leaf Goldenrod)
Solidago uliginosa (Bog Goldenrod)
Sagittaria latifolia var latifolia (Broad-leaf Arrowhead)
Potamogeton epihydrus (Floating Pondweed)
Juncus canadensis
Juncus effusus var pylaei
Carex baileyi
Carex canescens var canescens
Carex canescens var disjuncta
Carex comosa
Carex gynandra
Carex intumescens
Carex scabrata
Carex stricta
Carex trisperma (Three-seeded Sedge)
Dulichium arundinaceum (Three-way Sedge)
Scirpus cyperinus (Cottongrass Bulrush)
Cinna arundinacea (Wood Reed Grass)
Glyceria canadensis (Rattlesnake Manna Grass)
Glyceria striata (Fowl Mannagrass)
Sparganium americanum (American Bur-reed)
Typha latifolia (Broad-leaved Cattail)
Veratrum viride (White Hellebore)
Calopogon tuberosus (Tuberous Grass-pink)
Listera cordata (Hearleaf Twayblade)
Listera smallii (Kidney-leaf Twayblade)
Habenaria ciliaris (Yellow-fringe Orchid)
Habenaria clavellata (Small Green Wood Orchid)
Habenaria hookeri (Hooker's Orchid)
Habenaria lacera (Green-fringe Orchid)
The Allegheny "Corridor"
The distribution of species in western Pennsylvania's Allegeny Mountains and Plateau shows a concentration of certain species in a narrow salient of mesic highlands that extends from the plateau of northwestern Pennsylvania, through western Maryland and into West Virginia. It lies in the region southwest to northeast-trending isotherms and thus is characteized by rather uniform average temperatures. The salient is most apparent in Cambria and Somerset counties, and the latter includes the highest elevation in the State. In West Virginia the salient broadens in a complex of still higher mountains and plateaus extending into Virginia, and which, in its higher elevations and adjacent deep valleys, provides numerous refuges for elements of a boreal flora more characteristic of the Northern Appalachians. Of greatest interest here is the possibilty that this salient connecting nothern and southern highlands represents a migration corridor (Noss, 1983; 1987) for a diverse boreal and montane flora and fauna that moved southward during and after the ice age and which may serve a similar function for a northward movement during global warming.
In what follows we refer to representative species occurrence maps provided by Rhoads and Klein (1993). The maps presented here are examples of partcularly high concentrations of the given species along the salient, but numerous less well defined examples have been mapped as well. The four species illustrated, Dalibarda repens (Star Violet), Oxalis montana (White Wood Sorrel), Monarda didyma (Oswego Tea) and Milium effusum (Millet Grass), are all predominantly northern, as are most other species with this type of distribution. However Disporum lanuginosum (Hairy Disporum) is southern montane. Like the northerners, it is favored by the cool. mesic environment of the salient, and in marked global warming could migrate along it.
Unfortunately, the ecological state of the salient is much degraded through existing land use practices, although substantial forest cover and hence readily recoverable habitat exists in some areas.
Ecological Regions of Pennsylvania
Figure 1 (After Fike, 1999)
Dalibarda repens Distribution
After Rhoads and Klein (1993)
Disporum languinosum Distribution
After Rhoads and Klein (1993)
Monarda didyma Distribution
After Rhoads and Klein (1993)
Milium effusum Distribution
After Rhoads and Klein (1993)
Oxalis montana Distribution
After Rhoads and Klein (1993)
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