Forest— An Overview
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Major Forest Types
To the casual observer Appalachian Mountain forests appear as an almost uniform blanket of green covering hills, valleys and the loftiest ridges. They generally show little color contrast except in autumn and as a result the terrain appears to lack the scenic diversity of western landscapes with their sharp tree lines and soaring cliffs. There are exceptions to this uniformity in the high Alleghenies where jagged spruce spires form the skyline, in the striking water gaps which mark where rivers have cut through ranges and where resistant beds such as Tuscarora sandstone shine white above the trees. But these are exceptions. Yet there is an underlying, although cryptic, diversity in these forests that is in its way as impressive as that of any landscape. In part this reflects the different exposed rock types and in part mountain-related climate contrasts particularly in moisture availability. The degree of cloud cover may also play an important role. The diversity of habitats created by these factors results in a number of different forest types which are readily distinguished, even by the untrained eye when in close proximity to them. To illustrate, two deciduous forests could hardly differ more than those of the dry ridges of the Valley and Ridge and those of the moist slopes of the Allegheny Plateau. The ridge forests consist dominantly of shiny leaved, thick barked Chestnut Oak (Quercus prinus) or at higher elevations Northern Red Oak (Quercus rubra) with minor hickories and pines. Frequently trunks and limbs are distorted by harsh growing conditions and the forest floor is covered by a thick leaf mat. Few herbaceous plants penetrate this leaf mat but there is a variety of low heath shrubs such as Mountain Laurel (Kalmia latifolia), huckleberries and blueberries, which are favored by the additional light provided by rather thin canopies as well as the highly acidic soils. Where the leaf mat is thinner, light green cushion mosses (Leucobryum sp.), “Reindeer moss” (Cladonia sp), a lichen, or clumps of Curly-leaved Poverty Grass (Danthonia spp.) appear. In some places there are scattered little shiny leaved Teaberry (Gaultheria procumbens) plants with bright red aromatic berries. Fire is at home here as evidenced by many basal trunk scars and charred wood.
By contrast the medium moist (mesic) Allegheny forests are dominated by species such as Sugar Maple (Acer saccharum), Beech (Fagus grandifolia) and birches or in some cases by ash and basswood. Except for Beech these trees have thin juicy leaves that decay readily so there is little leaf litter except during autumn. In the case of maple and beech crown foliage is heavier than that of oaks and there is a green ethereal light even at midday. Ferns and spring wildflowers in great variety carpet the forest floor in places and heaths are replaced by viburnums and other tall shrubs. Trees, except for the oldest, are relatively smooth barked since they need to withstand fewer fires and abundant moisture allows them to grow straight and tall. Many species of birds, amphibians and other animals are far more abundant here than in the oak forests as indicated by the frequencies of bird calls. Yet the oak forests are rich in nutritious food sources such as acorns for Black Bears and other mammals.
The two contrasting forest types discussed above grade into even more differentiated types. Oak forest on exposed ridges in some places give way to open heath “barrens” in which heath bushes and stunted tress dominate, usually with scattered taller and wind-deformed Pitch Pine (Pinus rigida). Such terrain is in part the result of frequent fires. On the other hand the rich mesic Allegheny hardwood forest grades into spruce forest at higher elevations in which there are few shrubs or herbaceous plants but rather a thick ground cover of mosses and leafy liverworts with some ferns and lycopods. It is a dark forest of deep shade and cool moisture unlike any other in the Central Appalachians. Many other contrasting forest types are considered in our detailed inventories ("Forest Walks").
In addition to these large scale variations of major forest types, there is also a patchiness within them related to local rock and soil variation. For example in the Shenandoah Valley forest communities vary greatly depending on the nature and depth of bedrock. On uplands underlain by Ordovician Beekmantown dolomite cherty hilltops and deep soil may support White Oak (Quercus alba) -Black Oak (Quercus velutina ) forest with Red Maple (Acer rubrum) and ericaceous ground cover, indicating acid conditions despite underlying carbonate rocks. Talus slopes with SE aspect support a more mesic forest rich in hickories, Black Walnut (Juglans nigra ), Slippery Elm (Ulmus rubra), Bitternut Hickory (Carya cordiformis) and White Ash (Fraxinus americana ), while patches with near surface dolomite have Chinquapin Oak (Quercus muhlenbergii) and White Ash. These patches may be less than an acre in size and indicate alkaline conditions while all three forest types may occur in less than five acres.
The most complex and presumed parent forest of the Central Appalachians is the Mixed Mesophytic. This type derived from similar forests that occupied eastern North American and other centers such as Europe and East Asia since Tertiary times (Braun, 1950), although subject to climate-induced migrations. Thus many species of the European forests were eliminated when ice sheets forced them against inhospitable east-west mountain ranges and seas. However those of East Asia survived and many of the closest relatives of eastern North American species still live there. This correspondence between East Asian and American flora was recognized as early as 1846 by the famous botanist Asa Gray. The Mixed Mesophyte forest shows its most characteristic development in the Cumberland Mountains and in the Alleghenies of West Virginia below 2500 ft. (760 meters) asl. It also extends northward with attenuated diversity into Ohio, Maryland and Pennsylvania where it is increasingly confined to stream valleys. Eastward in Virginia it is largely restricted to topographic concavities such as coves, ravines and riparian zones, usually of the latest erosion cycle.
The Mixed Mesophyte forest is diverse with a number of species each of magnolias, oaks, hickories, walnuts, elms, birches, ashes, maples, basswoods, locusts and pines. There is also Tuliptree (Liriodendron tulipifera), Black and Sweet Gum (Nyssa sylvatica and Liquidambar styrocifula ), Black Cherry (Prunus serotina), American Beech and Canadian Hemlock (Tsuga canadensis). The most characteristic type indicators are White Basswood (Tilia heterophylla or T. americana var heterophylla ) and Yellow Buckeye (Aesculus octandra). However Yellow Buckeye does not generally occur in the Valley and Ridge. American Chestnut (Castanea dentata), once a major component, now survives only as stunted, disease-ridden sprouts. These major canopy species are accompanied by even more diverse understory tree, shrub and herbaceous layers as well as many fungi, mosses, etc. Typical components of the understory are the small trees Muscletree (Carpinus caroliniana ) and Sourwood (Oxydendron arboreum ), shrubs such as Spice Bush (Lindera benzoin ) and Paw Paw (Asimina triloba ) and the herbs Ginseng (Panax quinquefolius ) and Goldenseal (Hydrastis canadensis ) and many more. As previously stated, mesophytic plants, including the trees, tend to have soft, juicy leaves that on death rapidly decompose and, as distinguished from those of xeric oak forests, form only light litter but contribute to building rich soils.
Coinciding roughly with the most western part of the Virginia-West Virginia boundary, the eastern edge of the Mixed Mesophyte region forms a broad ecotone on transition to the Oak-Chestnut forest type of the Valley and Ridge. With the (let’s hope) temporary decline of the American Chestnut, which once flourished on its dry ridges, the Oak-Chestnut region is now characterized by the dominance of five oaks: Black, Scarlet, Northern Red, White and Chestnut and on the driest sites, by Virginia (Pinus virginiana), Pitch, Shortleaf (Pinus echinata) and Table Mountain (Pinus pungens) pines. Other prominent species are White Pine (Pinus strobus), Black Gum, Black Birch (Betula lenta), Pignut Hickory (Carya glabra ) and Red Maple. The understory tree layer is usually dominated by Service Berry, Flowering Dogwood (Cornus florida) and White Pine and in the shrub and ground layers by Mountain Laurel, Fetterbush (Pieris floribunda ) , huckleberries, blueberries, azaleas (deciduous rhododendrons), Teaberry (Gaultheria procumbens ) and other acid loving plants. Slope concavities may contain Tuliptree, White Ash, Cucumber Magnolia (Magnolia acuminata), Basswood and other mesic species.
Some authors (e.g. Kuchler, 1966) have split the Oak Chestnut region, into “Appalachian Oak Forest” and “Oak Hickory-Pine Forest” Types. Because I am optimistic about the American Chestnut’s eventual recovery from the Chestnut blight (Endothia parasitica), and because this species is a habitat indicator, Braun’s (1950) terminology is retained here.
Still farther to the east a second ecotone marks the transition to the Oak-Pine forest of the Piedmont. Since the latter generally lies below 1000 feet (300 meters) asl, it contains a number of species such as Loblolly Pine, Sweet Gum and Southern Red oak which are not found at higher elevations.
On ascent to the highest elevations and northward into Maryland and Pennsylvania southern species in the mixed mesophyte forest gradually drop out, northern species such as Yellow Birch (Betula alleghaniensis) and Mountain Maple (Acer spicatum) appear and Sugar Maple, American Beech, and Canadian Hemlock assume dominance. American Basswood (Tilia americana var americana ) replaces White Basswood as well. This is the Hemlock-White Pine-Northern Hardwood forest of Braun (1950). It has a distinctly northern quality in its shrubs and herbaceous flora and may appear identical to forests of the Adirondack foothills or New England. However this forest also contains a strong Appalachian element in both trees and herbaceous vegetation. Cucumber and Fraser Magnolia (Magnolia fraseri) and Black Locust are common and in some places. Great Rhododendron (Rhododendron maximum ) forms heavy understory thickets. In addition to typical northern herbs such as Canada Mayflower (Maianthemum canadense), the diversity is greatly enhanced by striking plants such as Frasers Sedge ( Cymophyllus fraseri ), with its elegant lily-like leaves, and seed-heavy stalks of Mountain Bugbane (Cimicifuga americana) which are endemics and missing from the northern forests.
Above 3500 feet (1000 meters) asl in West Virginia and at lower elevations in Maryland and Pennsylvania, the northern hardwoods yield gradually to the Red Spruce (Picea rubens) montane forest of boreal appearance mentioned earlier. In this forest circumpolar flowering plants such as Mountain Oxalis (Oxalis montana ) and Goldthread (Coptis groenlandica ) vie with lycopods, liverworts and mosses in the ground cover, while shrubs are rare because of dense shade. Southward this forest type occurs only in a few isolated and climate-modified stands as at Mountain Lake and Beartown (designated wildernesses) in the Valley and Ridge and in the Balsam Range in the Mount Rogers National Recreation Area of the Jefferson National Forest. At Mountain Lake there is a small isolated stand of old growth consisting of Red Spruce, Canadian Hemlock, Sugar and Red Maple, Black and Yellow Birch, White Ash, Northern Red and White Oak, Black Cherry, Cucumber Magnolia and Tuliptree. Mountain Maple and Great Rhododendron form the understory and the ground cover contains intergrowths of the boreal species Canada Mayflower ( Maianthemum canadense) and the southern Appalachian Galax ( Galax aphylla ), all at about 3600 ft. (1100 meters) asl. In the Balsam Range this forest, which here is almost restricted to elevations above 5000 ft. (1500 meters), assumes the character of the Southern Spruce-Fir type with the accompaniment of Red Spruce by Fraser Fir (Abies fraseri), the Southern Appalachian endemic. In this forest and also at lower elevations of this range other Southern Appalachian endemics such as Umbrella Leaf (Diphylleia cymosa) and a number of interesting salamanders enter the picture. Even the most northern appearing Central Appalachian Spruce forests, as on West Virginia’s Allegheny Plateau, contain an admixture of southern Appalachian species such as Mountain Holly (Ilex montana) and Southern Mountain Cranberry (Vaccinium erythrocarpum) which are out of the range of boreal forests.
In the oak-chestnut type forests of the Valley and Ridge and Blue Ridge Provinces the effects of elevation are more subtle, even cryptic. This is due in part to the different species segregates that result from lower precipitation and/or cloud cover and continentality as compared with the Allegheny highlands. Effects take the form of higher temperatures and influence of the nearby ocean on day to day weather, which tends to be somewhat erratic. In the vicinity of latitude 38˚N Tuliptree generally is confined below 2500 ft. (760 meters) and Chestnut Oak below 3500 ft. (1070 meters) asl. In these mountains there is with few exceptions, no spruce montane forest. Instead “orchard” type Northern Red Oak stands with gnarled, thick-trunked and widely spaced trees dominate the highest elevations. On the most exposed peaks trees are greatly stunted and directionally contorted by the wind. Many show long, thick limbs growing at right angles to the trunk as an adaptation to the weight of ice and wind stress.1 On elevations where rocky, acid soils or other inhospitable conditions are intensified, there are “barrens” of low heath shrubs, Sweet Fern (Comptonia peregrina ) and Bear Oak (Quercus ilicifolia ). These shrub expanses are punctuated by taller wind-contorted (banner) Pitch and Table Mountain Pines, or in some cases, shrubby Hemlock. Above 3500 ft. (1070 meters) asl low elevation shrubs and herbaceous flora are replaced by such northerners as Mountain Ash (Pyrus americana ), Mountain Maple, Yellow Clintonia (Clintonia borealis), Canada Mayflower, etc. as in the Alleghenies. Perhaps because of relatively high precipitation there, the northern Blue Ridge is favored by a number of rare disjuncts. On it are found Virginia’s only known occurrences of Bearberry ( Arctostaphylos uva-ursi ) and Balsam Fir (Abies balsamea ), the latter its most southerly station on the Planet. It is confined to the summit regions of Hawksbill and Stonyman Mountains which barely extend to 4000 feet (1200 meters) in elevation and is a minor component of oak forest. Consequently it must have passed through a rather narrow thermal bottleneck during the hypsithermal interval, a period of higher temperatures.
It is obvious that changes in vegetation with elevation is not solely due to lapse rate. Certainly the restriction of Tuliptree below 2500 ft. in the valley and ridge at 38˚ N and its occurrence above 3000 feet (900 meters) at the same latitude in cooler West Virginia requires another explanation. The survival of seedlings frequently depends on the interaction of temperature, soil and air moisture and light intensity. Although the Valley and Ridge and the Blue Ridge are less continental than the Appalachian Plateau, their weather varies greatly from day to day. Warm spells that activate buds are frequently followed by hard frosts and frost heaving that damage buds and roots. When the disrupted roots freeze again less moisture than otherwise reaches the plant above ground. These conditions are more prevalent in the Valley and Ridge and Blue Ridge than on the Allegheny Plateau where there is more snow and cloud cover.
Unusual Biologic Communities
Within the areas of the major Central Appalachian forest types there are many smaller biologic communities with special characteristics. Invariably these communities have resulted from geologic, topographic or climatic conditions that are unique in their details. Most widespread are the glades or natural openings that result from such conditions as interrupted drainage or bedrock-imposed moisture or drought conditions. In terms of area the most common glades are the high-elevation bogs, fens, swamps and other wetlands of the Allegheny Mountains and Plateau. There are also many smaller open or forested wetlands, usually associated with floodplain topography, artesian springs, perched water tables or sinkholes. Many of these communities, both large and small, contain rare, frequently disjunct, species. An example is the famous Cranberry Glade complex that covers 750 acres (330 hectares) on West Virginia’s Allegheny plateau. Lying at 3400 ft (1040 meters) elevation, its boreal type bogs fens, marshes and swamps are rich in acid soil disjuncts such as Bog Rosemary (Andromeda glaucophylla) and Small Cranberry (Vaccinium oxycoccos) as well as some with greater soil tolerance ranges such as Buckbean (Menyanthes trifoliata), a circumpolar relative of gentians. Of similar nature, and the largest wetland in the Central Appalachians, is the 7000 acre Canaan Valley complex. At 3200 ft. elevation and lying just north of the Monongahela National Forest, the Canaan Valley is the site of a new national wildlife refuge.
Some of the smaller wetlands are also great centers of diversity. An example occurs alongside Folly Mills stream in the heart of the Shenandoah Valley. This small wetland, at only 1580 ft (480 meters) asl, is home to an impressive array of northern disjuncts as well as southern species, many of which were first identified only a few decades ago and which are still being inventoried. As in the Cranberry Glades, Buckbean also occurs here, but in an almost acid-neutral environment of a calcareous marsh and fen. Here also are such indicators of this environment as Prairie Loosestrife ( Lysimachia quadriflora) and Swamp Lousewort (Pedicularis lanceolata). Other northerners include Glaucous or Pussy Willow (Salix discolor), in its only known Virginia occurrence2, as well as a number of rare sedges3. Southern species which form a melange4 with these northerners are Purple Gerardia (Gerardia purpurea) and the rare Large-leaved Grass of Parnassus (Parnassia grandifolia) which is a member of the saxifrage family. This complex community owes its origin and continued existence to cool artesian springs and location in a “frost pocket” by virtue of air drainage from surrounding hills. These factors have combined to provide a refugium for species that we may infer were originally driven south by the climatic conditions brought about by ice sheets to the north. However, unlike northern type communities at higher elevations, this refugium is confined to the wetland while the surrounding hills are covered by Appalachian type oak-hickory forest which contain such southerners as Post Oak and Persimmon but no species of northern affinity.
Sinkhole ponds along the western edge of Virginia’s Blue Ridge harbor such rare disjuncts as White Buttons (Eriocaulon septangulare), Eastern Tiger Salamander (Ambystoma tigrinum tigrinu ) and Virginia Sneezeweed (Helenium virginicum). Other, even rarer, small ponds and wetlands occur at various elevations, perhaps on perched water tables and provide habitat for long isolated populations of salamanders and other species. All are under threat of poor management practices and roads that expose them to Off Road Vehicles (Mueller, 1991).
Dry cedar glades, limestone and shale barrens contain assemblages of draught, cold and heat resistant plants and animals. Some of the most outstanding examples occur in West Virginia’s Smoke Hole region in the Valley and Ridge Province, (Bartgis, 1993). There limestone barrens and cedar glades support a number of midwestern and western species, some of which, like Prairie Flax (Linum lewisii) are disjunct from as far away as west of the Mississippi River and the shore of the Hudson Bay. The floras of the more common shale barrens have received considerable attention in recent years and are known for rare species such as the federally endangered Shale Barren Rock Cress (Arabis serotina) (Wieboldt, 1991).
Other special habitats on exposed ridges and peaks, frequently on rocky terrain, harbor montane and boreal plants such as Michaux’s Saxifrage (Saxifraga michauxii), Greenland Sandwort (Arenaria grœnlandica) and Three-toothed Cinquefoil (Potentilla tridentata). However natural “balds” with extensive grass and shrub communities in place of trees, such as characterize high elevations in the Southern Appalachians, appear to be very rare in the Central Appalachians (Rentch and Fortney, 1997). There are numerous more limited openings, exclusive of the previously described heath barrens and which are more mesic in character than the latter. These merge with the more widespread orchard type summit forests of Northern Red Oak or in some cases Beech and Hawthorn (Strausbaugh and Core, 1977). These may have ground covers of grasses such as Mountain Oat Grass (Danthona compressa), Hay-scented Fern, sedges and cushions of Haircap Moss (Polytrichum).
More common than the conspicuously novel communities discussed above are some that are merely unusual in the forest type in which they occur. Frequently they involve only slight disjunction of common or rare species in a setting of or in combination with the dominant regional flora. Thus distinctly northern species may occur in a mixed mesophyte forest with dominantly southern species. An example is the occurrence of northern herbs such as Wild Sarsaparilla ( Aralia nudicaulis) and Millet Grass (Milium effusum) with Tuliptree and Black Walnut as in the lower Back Creek drainage of Virginia’s Valley and Ridge or Canadian Yew (Taxus canadensis) and Mountain Maple at less than 2500 ft. (760 meters) asl in certain steep sided NE facing gorges that cut through Allegheny Mountain in West Virginia.
From the occurrences of melange communities a sequence of types is distinguishable that may elucidate the so-called “disharmonious” Pleistocene communities which they resemble and of which they may be relict. According to MacArthur (1975) there is a positive correlation between increased species diversity and decreased climatic variability as measured by winter-summer differences in mean temperature. The most striking case and end type of the identified sequence here is the small isolated Folly Mills Wetland where the effects of seasonal fluctuations in growing conditions are moderated by the artesian springs and salubrious chemistry. Thus although the surrounding forest, which is more subject to climatic variations, is typically southern Appalachian, the wetland is a melange of many northern and even Arctic species with other species of wide as well as decidedly southern distributions.
Next in the sequence, with markedly less disjunction, and unlike the Folly Mills wetland, not separated from the regional forest, is the occurrence of northern mesic species such as Aralia nudicaulis and Millet Grass in a southern Appalachian mesic forest as the cited occurrence in the Back Creek drainage.
Finally, least remarkable but most common, is the occurrence of rare and common northern species, some only slightly if at all disjunct, in high elevation wetlands such as the Cranberry Glades or in the surrounding forest with which the wetlands harmonize in climatic type. However as pointed out earlier, all Central Appalachian northern type communities also have admixtures of southern Appalachian species.
Tolerance of shade by forest trees, shrubs and herbs plays an important and easily observable role in forest ecology. It directly influences what species can grow in different forest environments at various times of the year and stage of development. It to a large extent determines how a forest looks and its manifestations should be clearly observed by those who would understand the forest.
If trees are tolerant of shade while young they are able to survive, at least for a time, as seedlings and saplings beneath the forest canopy. If not, they can flourish only in openings. Some trees are in fact quite tolerant while young but become increasingly intolerant with age, certainly a useful adaptation. Of course tree seedlings are opportunistic and when a mature tree falls those already growing in the resultant opening respond to the increased light by a growth spurt. Some tree species never grow large and form a forest understory. Such species — Flowering Dogwood, Hophornbeam and Striped Maple are examples — are shade tolerant by necessity, as are all shrubs that grow in the forest. Some forest herbs, those soft leaved annuals and perennials that far outnumber trees in species diversity, are quite shade tolerant while many are not. The most tolerant are ferns and lycopods but many flowering plants form a vernal flora that must flower and set seed before the trees leaf out. Comparatively few are able to do this under summer’s dense canopy.
Due to low shade tolerance many oak forests look remarkably different from maple forests. Since oak seedlings— with the exception of Northern Red Oak— tend to have low tolerance, there will be few present in a mature oak forest of the same species. On the other hand a maple forest may have a heavy undergrowth of maple seedlings and saplings. In the oak forest seedlings and saplings will be confined to openings creating a patchiness different from that of the maple forest. In addition a number of other shade intolerant species will occupy these oak forest openings creating a type of diversity less well developed in the maple forest.
Shade tolerance also governs succession, or the change in species makeup after a disturbance creates an opening. In general shade tolerant species tend to be more abundant in late as compared with early successional stages. However the most complex forests, such as the mixed mesophytic, have a diverse array of species with wide shade tolerance ranges since disturbances are frequent enough to perpetuate intolerant as well as tolerant species.
In the Central Appalachians the most shade tolerant species of trees are those which characteristically occur in the medium moisture or mesic regimes. They are Canadian Hemlock, American Beech, Sugar and Black Maple, Red Spruce and Balsam Fir as well as a number of small understory trees among which Flowering Dogwood, Hop Hornbeam and Striped Maple are most common. The Basswoods and Yellow Buckeye are also quite tolerant. Most species of oaks are of intermediate tolerance. However Scarlet Oak shows low tolerance of shade, as do Tuliptree, Black Cherry, White Ash and most of the Birches. Shagbark Hickory, a tree of rich mesic environments, is moderately tolerant but other members of this genus as well as the related walnuts are fairly intolerant. Some species, such as White Pine and White Ash, are very tolerant when young but become intolerant with age.
Red Maple, which is of intermediate tolerance, but more tolerant than any oak, has a special role. It is at home in habitats ranging from Southern Swamps to the dryest mountain ridges and the fringes of the boreal forest. Because conditions exclude the most tolerant species such as Beech and Sugar Maple, it, along with Striped Maple, is frequently the most tolerant species in xeric oak-chestnut forests of the Central Appalachians. As a consequence it has become a prime scapegoat and cover for a multitude of silvicultural sins perpetrated by the U.S. Forest Service and other industrial foresters.
Despite the great variation in shade tolerance among trees, virgin mixed mesophyte forests have an abundance of species of all shade tolerance levels. Thus Tuliptree and intolerant oaks are major components of many stands although shade tolerant species frequently dominate. In the dry oak-chestnut forests intermediate and intolerant oaks (White, Chestnut, Black, Red and Scarlet) dominate in stands undisturbed by humans since the most tolerant species are excluded by soil and climate. This fact is a source of embarrassment to the Forest Service which steadfastly maintains that the commercially desirable but intolerant oaks need the help of large openings such as clearcuts to reproduce and prevent takeover by Red Maple and other undesirable species. However the prominent ecological forester Dr. Leon Minckler has repeatedly made the point that large openings are not necessary for reproduction (e.g. Minckler, 1974). It is becoming increasingly clear that a major mechanism of forest reproduction in mature deciduous forests is the formation of tree fall gaps which allow sufficient light to encourage even the least tolerant species.
At every stage of development forests are subject to a variety of natural disturbances that result in tree damage or death. Usually dead trees fall after standing for periods as “snags.” In many cases healthy living trees are knocked down by winds, lightening or the weight of snow and ice. They may also be felled by Beavers. Trees may be killed while standing by a great variety of insects or pathogens such as fungi or by fire.
Disturbances may be regarded as divided into two types. The most prevalent type may be called background disturbances. This includes the tree damage and mortality of a single or small group of trees without the intervention of large scale insect, storm, fire or other disturbances that affect many trees at a time. It should be remembered that more than 99 percent of all trees in a healthy maturing forest must die to make room for the survivors. The trees that die are usually the weakest and are subject to insects and disease that do not affect stronger trees or they may be uprooted due to weak root systems. On this background of normal tree death are superimposed the large episodes of disturbance due to hurricanes, tornadoes, large fires and widespread insect and disease outbreaks.
The prevalent natural disturbance type in the Central Appalachians may then be summarized as follows:
Single or small group tree damage or death by a variety of agents including but not confined to insects, pathogens, wind throw, fire and ice or snow loading.
Examples of Large Disturbances
- Ground or crown fires
- Thunderstorms or tornadoes
- Ice or snow loading
- Gypsy Moth (Lymantria dispar)
- Beech Scale (Cryptococcus fagi)
This spreads the fungus Nectria coccinea var. faginata and is called the “Scale-Nectria Complex.”
- Southern Pine Beetle (Dendrocotanus frontalis)
- Black Turpentine Beetle (D. terebrans)
- Hemlock Woody Adelgid (Adelges tsugae)
- Chestnut Blight (Endothia parasitica), a fungus
- Beech Blight (Nectria coccinea), a fungus spread by Beech Scale ( see above)
- Dutch Elm Disease (Ceratocystis ulmi), a wilt fungus
- Dogwood Anthracnose (Discula distructiva)
In addition to these specific organisms of disturbance there has in recent years emerged a sort of catch-all and vague concept of “oak decline” and this has been stressed by timber interests, including agencies such as the U.S. Forest Service, as justification for cutting trees. Oak decline is said to be characterized by symptoms such as chlorosis, limb die-back and epicormic branching, mostly in the Red Oak group. Forest Service experts have yet to find a solid explanation for the condition but are forced to fall back on a broad spectrum of insects and diseases triggered by such factors as drought and poor site quality (Starkey et al, 1989). It is said to be quite prevalent in the Southern Appalachians where Zahner (1992) proposed “benign neglect” as a proper curative agent. He attributed many of the symptoms to normal senescence of comparatively short-lived species such as Scarlet and Black Oak in the process of replacement by longer-lived Chestnut and White Oak. Certainly there is little attempt by the public agencies to look for causes of oak decline in past management practices which have brought about pervasive and extensive changes in soils, moisture regimes and even forest type over wide areas. As Lucy Braun recognized long ago, many rich mixed mesophyte forests have been degraded to depauperate and Xeric oak-pine stands that consist mostly of the short lived species referred to by Zahner. Thus oak decline may actually be a manifestation of a healing process of reversion to a more complex forest type in the normal succession from simple, excessively oak-rich stands that have resulted from human activities. We shall see that in many areas where the Forest Service has identified Oak decline in the Central Appalachians they have used a heavy dose of imagination and have failed to distinguish it from normal limb shedding and mortality in a healthy forest.
Background disturbance gives rise to much of the structural diversity of Central Appalachian forests as especially well developed in old growth stands. Windthrow and defoliation create gaps in the canopy which allow opportunistic light demanding as well as shade tolerant species to spring up. This increased diversity is further accomplished by the pit and mound structures created by tree falls and associated uprooting. These structures not only bare mineral soils obligatory for certain plants, but create breeding and feeding habitats for arthropods and amphibians in the pits.
Runkle (1996) has pointed out that the formation of small tree-fall gaps by windthrow or otherwise probably is dominant in the creation of forest openings in the Central Appalachians.
Wind, Ice and Snow
Perhaps the largest natural disturbances in the Central Appalachians result from hurricanes which from time to time cross into the mountains. In such events thousands of acres may be affected in the most vulnerable topography. An example is Hurricane Hugo which entered the Valley and Ridge in September,1989. In some cases serious landslides accompany hurricanes as a result of heavy rainfall. These landslides are particularly extensive on the east side of the Blue Ridge as in the case of Hurricane Camille in 1969 (Kochel and Simmons, 1986). Smaller, but still extensive areas of tree breakage and uprooting occurs from local thunderstorms and tornadoes. However extensive blowdowns are not as common as in the boreal forest where generally more subdued terrain permits greater wind sweep and trees which are predominantly conifers are not as wind firm.
Many parts of the Central Appalachians, particularly at high elevations, are subject to severe ice and snow damage. Ice from glaze storms is most common and when the wind blows many limbs come down. Snow damage tends to be confined to evergreens and to deciduous trees in fall when early snow loads trees still in leaf. The sometimes bizarre tree forms that result have already been alluded to.
Role of Fire
Next to tree fall gaps, usually formed by windthrow, fire was probably most responsible for natural forest openings. Abrams (1992), in particular, has stressed the role of fire in the maintenance of oak forests. While the role of fire in the Central Appalachians is still poorly understood, extensive observations by Virginians For Wilderness have revealed a number of interesting effects of this agent. Quite obviously fire was most common in the dry oak-chestnut and oak-pine uplands before human suppression became routine. However, many trees in moist coves also show fire scars. This is probably a consequence of the relatively thin bark of many cove species such as Shagbark Hickory, Beech, Tuliptree, etc. as compared with thick-barked Chestnut Oak for example. Although the virgin high elevation spruce forests of the Allegheny Plateau presumably had substantial fire potential, it appears that the prevailing high moisture levels prevented many fires until logging and land clearing produced incendiary slashings and ignition sparks.
In addition to charred wood, evidence for forest fires frequently takes the form of inverted U-shaped basal trunk scars or cavities. These scars are usually confined to a single (lee?) side of trees for any given fire. Other evidence is the nature of sprout clumps in which the sprouts of individual clumps are widely spaced. This spacing indicates that, unlike sprouts that follow logging, fires tend to kill the lower parts of trees so that sprouting is from surrounding roots. Where such sprouting occurs, it points to high fire frequencies in the past since trees in excess of 100 years of age seldom sprout much. Such evidence has a bearing on the identification of primary and old growth stands. However, contrary to some opinions, fires set by indigenous Americans or otherwise were not required to protect many Appalachian oak forests from invasion by more shade tolerant species, a point already made in the section on shade tolerance.
Although oaks are fairly resistant to fire — and this applies particularly to Chestnut Oak with its thick bark ridges — they are not as all-around fire adapted as Shortleaf, Pitch and Table Mountain Pines. Examination of these pines reveals multi-layered and hence highly insulated bark. Consequently, although oaks in a burn area may show fire scaring and even high mortality, coexisting Pitch and Table Mountain Pine show only blackened lower trunks with no visible damage to living tissues.5 As a result of this fire resistance pine may be the oldest and largest trees on some dry sites. Also, since they have serotinous cones, and in the case of Pitch and Shortleaf Pines, sprouting ability, they are ever ready to renew themselves should an intense fire occur. By contrast White Pine is not nearly as fire adapted.6
In recent years the Gypsy Moth has had the most visible effect on certain Central Appalachian Forests. Because of its fondness for Oak leaves this defoliator has made its greatest impact on the Valley and Ridge province where these trees dominate. Usually two successive defoliations are enough to kill a tree. Furthermore, although the Moth larvæ finish feeding in early or mid summer and the trees then attempt to grow new leaves, this depletes the supply of energy to the extent that, unlike Chestnut Blight-Killed trees, these trees retain no power to sprout. Since the Gypsy Moth is an alien species, it has few effective native predators. However several pathogens, a fungus and a bacterium, have been introduced and are quite effective. In particular, the fungus Entomophaga maimaiga, originally imported from Japan in 1910, brought about a collapse of Gypsy Moth populations over large areas, including parts of the Central Appalachians, in 1996 (Hajek, 1996; Schneeberger,1996; also see <www.nysaes.cornell.edu/ent/biocontrol/pathogens/e_maimaig_>). These pathogens, in concert with native birds, insect predators and other factors generally bring about population crashes after two or three seasons of severe defoliation. Because conditions vary so widely it is difficult to predict the number of years between population peaks.
While the Gypsy Moth kills many trees and damages many more, its effect is not all negative on our forests. The open canopy that results from defoliation and tree death allows saplings and many other species on the forest floor to grow vigorously into lush undergrowth, although the acorn crop on which some wildlife depends may be greatly reduced. Also many birds and animals benefit greatly from the abundant wood boring larvæ made available and salamanders and other small animals flourish in the cool earth beneath the fallen tree trunks. At the same time these trunks, lying in every direction, provide excellent cover for large animals such as Bobcats and Black Bears. Indeed the Gypsy Moth attacked forest acquires many of the desired features of old growth. Not least is the winnowing effect of the Moth in eliminating the most susceptible trees, thereby strengthening the genetic stock of the forest.
Although the Gypsy Moth is having a substantial effect on forest ecology, the Hemlock Woody Adeligid, also an alien species, may ultimately have a far greater impact. Unlike the Moth this Adelgid does not spread rapidly since its flying forms require spruce species as hosts that are not present in the region. Also its immature forms do not have the capability of “ballooning” or blowing away on silk strands, that Gypsy Moth larvæ have. Consequently it is spread mainly through transport of its eggs and nymph stages by birds and the wind spread of tree fragments to which it adheres. Reviews of the life cycle of this Adelgid are widely available on the internet.
The distribution of the Hemlock Woolly Adelgid is very spotty and irregular. It is widespread in Shenandoah National Park and along the Blue Ridge generally where it has devastated old growth Hemlock. In the Valley and Ridge it has devastated Hemlock in certain stream valleys such as Ramsey's Draft, a designated Wilderness Area, but appears to colonize ridges above 3000 feet (915 m) asl more slowly. Unlike the Gypsy Moth, which does not kill many of the trees it defoliates, the Hemlock Woolly Adelgid appears to be far more lethal. This lethality results at least in part from the low capability of conifers to store energy in their roots and the lack of a true dormant period in them. It is likely that the Hemlock Adelgid will result in the extirpation of this grand conifer in many rich cove areas with subsequent replacement by oaks, maples and Tuliptree. This would not however be the first time this species suffered serious decline. Pollen data indicate that some pathogen or insect brought about a population crash in Hemlock over wide areas of eastern North America about 4800 years ago (Davis, 1981).
Compared to the Gypsy Moth and the Hemlock Woolly Adelgid the effects of the Southern Pine Beetle and the Black Turpentine Beetle in the Central Appalachians are relatively minor. Since they are natives, extirpation of the host species is not likely to occur. Generally confined to the Piedmont and Coastal Plain, intrusion of the beetles into the mountains is confined to a run of mild winters such as occurred in the late 1880s and early 1990s, but in 1994 was halted by a cold winter. Whereas the Gypsy Moth and the Hemlock Woolly Adelgid attack foliage, these beetles riddle the bark, destroying the cambium, and this kills quickly. Fungus and wood borer attacks quickly follow and destroy the wood on a massive scale. Attacks are usually concentrated in the Yellow Pine group (Virginia, Pitch, Shortleaf) but may also occur in White Pine if infestations are severe. The Black Turpentine Beetle concentrates on the lower trunk while the Southern Pine Beetle attacks the middle and upper trunks. Since pines are a minor component in Central Appalachian forests and are native, there are probably no negative long term impacts and they conceivably benefit the ecosystem through habitat enhancement by the dead wood produced. However short term economic loss may be severe in pine plantations.
Many diseases affect trees during their normal course of development and these play a major role in background disturbance. Some diseases achieve enough prominence to greatly disturb the forest. The most familiar example is the fungus that produced American Chestnut Blight and which had its origin in Eurasia. There it coevolved with the native chestnuts which consequently developed resistance to it. By the 1930s Chestnut Blight had swept through eastern North American deciduous forests and most American Chestnut trees were dead. However the smaller shrub-like Chinquapin (Castanea pumila) was little affected.
When attacked by the Chestnut Blight the American Chestnut suffers limb death and finally the entire trunk above ground dies. As a consequence there is no possibility of refoliation but the roots live on and their energy and nutrient supplies are retained as is their ability to sprout. Furthermore this sprouting ability appears to be retained for years or indefinitely. Thus even today, more than 60 years after the original infection, some trees continue to sprout and occasionally even set fruit. But these fruits seldom contain viable seeds because the trees are now too far apart for mutual fertilization. Some of the sprouts attain heights of 40 feet and 8 inch diameters. Virtually all die off eventually but leave healthy roots behind to sprout again. There is still a possibility that a weakened strain of the virus may take over and that the small amount of viable seed produced will yield a resistant strain of Wild American Chestnut. Let’s hope it does!
Today the sprouts of the American Chestnut are encountered almost everywhere in the Central Appalachians. They are most abundant on moderate mountain slopes where the Oak-Chestnut forest type is best developed but are also common on exposed ridges. They are less common in rich coves and in the mixed mesophyte and northern hardwood forest types. A broad survey of West Virginia forests, including many virgin tracts, by Brooks (1910) indicates that at the time of settlement by Europeans, American Chestnut was an ever present but seldom major component in the dominantly mesophytic forests of that state. This is in agreement with the survey of Braun (1950) of mixed mesophyte forests of the Cumberland Mountains and Plateau. In addition to the sprouts which probably originated mostly from immature trees, there are still many large Chestnut trunks and large limbs on the ground. The largest Chestnut remains preserved due to the tree’s extraordinary resistance to decay, are to be found in cove areas where the trees grow to largest size.
No attempt will be made to discuss in detail the many pathogens which are active in Central Appalachian forests and which play such an important role in maintaining as well as challenging forest health. As indicated in our tabulation other pathogens of some importance are Dutch Elm disease and Beech Blight. Dutch Elm disease is of rather minor importance in the Central Appalachians since it primarily affects American Elm (Ulmus americana), a tree almost confined to river bottomlands at lower elevations. Its effect on Slippery Elm (U. rubra), the most common member of the genus in the region, appears to be minimal and in most areas nonexistent. Also Beech Blight has so far apparently had little impact in the region and appears to be concentrated in the northern Appalachians. However this pathogen may pose a greater challenge to the region’s forests in the future.
Human disturbance of the forest is so pervasive and complex that it cannot be adequately discussed here, however, a partial treatment has been provided elsewhere on this web site (Central Appalachian Forests, a Guide for Activists, Mueller, 1994).
Glaciers and Forest Migration
The largest disturbances to which the Appalachians forests were subjected are the ice-age and post ice-age forest migrations. These migrations are part of the diverse phenomena related to the proximity of the ice and its withdrawal. Temperature variations were important as were air mass movements such as particularly the descending dry winds that blew off the ice caps. Pollen data (Delcourt and Delcourt, 1981) indicate that around the glacial maximum a boreal Jack Pine -spruce parkland (as distinguished from a closed canopy forest) extended as far south as Tennessee and tundra probably occupied the highest Appalachian elevations. At that time the current deciduous forest of these mountains lay far to the south along the Gulf and lower Atlantic coastal plains with the mixed mesophytic component probably confined to dissected major river system blufflands. However, even as the ice sheet reached its points of greatest advance, a warming trend had already set in. When the temperature reached a maximum (the hypsithermal interval) some 7000 years ago, existing forest types were temporarily displaced northward perhaps 200 miles (300 km.) and to several hundred meters higher elevations. Furthermore similar displacements of this type probably occurred a number of times in the last 10,000 years ( Pielou, 1991). Thus there emerges a picture of a geographically dynamic forest that was able to migrate hundreds of miles and reconstitute itself on a time scale of several thousand years or less.
Associated with the great forest migrations after the glacial maximum, there, in all probability, were corresponding changes in soil types. Evidence comes from a number of studies in glaciated regions in which all soil changes occurred less than ten thousand years ago (Armson, 1979) . The speed with which such changes can occur was illustrated by Langmaid ( 1964) who showed that earthworms could obliterate upper horizons of podzol in as little as three years. Also in their studies of soils in a forest-prairie ecotone in Minnesota Severson and Arnemann (1973) found that transformation of mesic deciduous to pine-hardwood forest was accompanied by alterations of the soil profile to one meter depth in less than 2000 years. These results lead one to believe that soil adjustments could easily have kept pace with changes in vegetation type in the Central Appalachians during the last eighteen thousand years.
Forest Succession and Secular Change
The result of natural and human-induced disturbances is succession, the progressive change of biological habitat from one occupied by pioneering species to some form of “climax” community. In forests this progression is usually from shade intolerant to tolerant species since many intolerant species are adapted to the high light intensity and degraded soils of forest openings. However many tolerant species also do well in openings, especially if they originate from sprouts, or if, like Red Maple, are adapted to harsh conditions. It was once rather naively thought that eastern North American deciduous forests inevitable progressed toward a Beech-Maple climax, an idea that gained credence chiefly in the Northeast where this climax is common because of the climate and limited species richness (and where many foresters lived). However it was subsequently learned that the climax community of the mixed mesophyte forest includes many common intolerant species. Also, as stressed by Lucy Braun, some major forest types, such as Oak-Chestnut, may at times be what is sometimes referred to as physiographic climaxes (see our later critque of designating different types of climax) consisting of shade intolerant species such as oaks and pines. In all these eastern forest types, treefalls, fires and blowdowns and other disturbances are frequent enough to perpetuate intolerant species.
The nature of succession is quite different in deciduous and in coniferous forests. It also differs markedly in naturally disturbed forests and those disturbed by humans. Deciduous forests have the capacity to resprout from stumps and roots as long as these survive the disturbance. Coniferous forests, with the rare exception of certain species such as Pitch Pine, have little or no sprouting capacity. If forest floors of deciduous forests are not disturbed too much succession may be short circuited with simple seeding and resprouting of the original trees and survival of understory and herbaceous species. Most animals such as arthropods, amphibians, and mammals may also survive or rapidly recover from such light disturbances. In such cases incursions by early successional direct sunlight-dependent species may be very limited. However where the forest floor has been greatly disturbed succession may not only be set to zero or bare soil but fail to attain advanced stages for hundreds or even thousands of years. Documentation of the extremely long recovery time for herbaceous forest interior vegetation after logging has been provided by Duffy and Meier (1992) who have shown that it may be hundreds of years for certain species. Analogous studies of salamanders by Petranka et al (1993) also demonstrated long recovery times. Raymond and Hardy (1991) showed that mole salamander populations even in uncut forests adjacent to clearcuts were greatly affected by these cuts.
When coniferous forests are disturbed, the response is quite different from deciduous forests. Because felled or killed standing conifers don’t sprout, a conifer forest can be propagated only by the seeds, seedlings and saplings which may be present at the time of disturbance. Usually there are few of either seedlings or saplings since they tend to die off in the dense shade. When they are present seedlings are apt to be so small that they are easily overtopped by deciduous trees once openings are made. Although the latter may not originally be present, they find rapid access to cleared coniferous forests since many, such as aspens and maples, have wind transported seeds, or like cherries, have fruits spread by birds. The best examples of this response of coniferous forests in the Central Appalachians occur in the high elevation spruce belt of the Allegheny Mountains and Plateau of West Virginia. Here a relatively undisturbed Red Spruce forest had existed for at least hundreds of years before the advent of European settlers. Because of high moisture values this forest escaped severe fires. Apparently also large blowdowns were infrequent. However due to logging, which extended from the late 1800s to the 1960s, some parts of this belt suffered extensive and very hot fires which were set in slash by sparks from engines used in these operations. Even where fires did not occur, spruce was rapidly replaced by a variety of deciduous trees and shrubs after logging. The trees of the forest which came in after the spruce was cut were mainly northern hardwoods such as Yellow Birch, Sugar Maple, Beech, Fire Cherry (Prunus pensylvanica), Aspens (Populus tremuloides and P. Grandidentata ) as well as other rapidly growing species brought in by wind and birds. Where fires had burned hot even the deep organic soils of the spruce forest were burned away. In such cases, as at Dolly Sods just west of the Allegheny Front in Tucker County, West Virginia, the higher water table that resulted from tree loss brought about acidification and extensive heath barrens populated by blueberries, huckleberries and even cranberries and sphagnum moss. In some places bog species occur even on quite steep slopes. The acidification in water saturated soils results from the lack of capillary action in them so that bases such as Calcium Carbonate are not brought up from below. The replacement of spruce by hardwoods had been extensive during the early part of this century. This is well shown by comparison of a map presented by Brooks (1910) with Landsat satellite photographs of the same area.
Although Red Spruce forest in the Alleghenies was in many ways replaced by northern hardwoods, slow reoccupation by spruce seedlings as understory in the hardwoods is occurring. This is possible because some species such as birch do not cast dense shade and because the spruce is very tolerant.
When a forest is disturbed by natural forces there is seldom much damage to the forest floor and unlike human disturbances, which are usually linked to the outside by roads, natural disturbances tend to be more isolated. Thus they are less subject to incursions by alien species in their early successional stages when they are most vulnerable to these. In Central Appalachian deciduous forests newly disturbed areas are likely to be populated by many species of the Aster family, by Poke ( Phytolacca americana) and other native herbs. In the case of acidic oak forests these will be followed by a flourishing of various heath shrubs that may have been present in the original forest. These herbs and shrubs will be accompanied by vigorous growth of sprouts and seedlings of forest trees as well as opportunistic trees seeded from the outside by wind or birds. Early succession in a disturbed coniferous forest may be similar, except that there may be few conifer seedlings present and many herbs will be discouraged by acid conditions. In this case heath barrens may result as previously described in the case of Dolly Sods.
There is a fundamental difference also in forest succession which results from direct physical disturbance such as wind, fire or insect attack and that which is a consequence of secular temperature or moisture change such as characterized the glacial advance and retreat. In the latter case some species gradually die off and are replaced by others, perhaps without the intervention of true early successional stages. This is analogous to what occurs in late stages of normal succession when mature intolerant species such as certain oaks are replaced by more tolerant species such as maples.
Secular changes in forest type may be — and probably are— underway in the Central Appalachians. A possible instance may be the development of Red Spruce understory in old growth or mature upland oak-rich forest as in the Fanny Bennett Hemlock Reserve in the Monongahela National Forest (see our section on this forest) where it cannot be easily attributed to recovery from human induced episodes of deforestation and fire. However this instance may reflect recent fire control measures and so represent a shift of equilibrium under a modified disturbance regime. An alternative explanation is that such expansions of the spruce forest reflect a recent change to cooler and moister conditions. A somewhat similar case of Red Spruce invasion of oak forest occurs in the Shenandoah Range of the Valley and Ridge. The source of the invading spruce is a rare primary stand consisting of mature Red Spruce, White, Black and Northern Red Oak, Yellow Birch, Red Maple and Hemlock with and understory of Great Rhododendron and Mountain Holly (Ilex montana). This forest occurs at about 3600 ft. asl. with a southeast aspect in a springy area known as Hall Spring (see our section on this forest). It is the only substantial spruce forest in this relatively dry range. The surrounding dominantly Northern Red Oak forest is being invaded by seedlings of Red Spruce from the primary stand. However the Red Oak forest is in this case secondary and the spruce understory may result from fire suppression.
Many transformations such as those involving changes in soil and forest type as discussed earlier appear to be far more rapid than secular genetic adjustments since the end of the glacial period or even the earlier glacial maximum. Soil change depends on favorable kinetics of chemical and micro-organic reactions embodied in organisms such as fungi, bacteria and earthworms while transformations of forest type depends largely on seed dispersal and suitable soil development. In contrast, genetic change results from selection pressures acting on successive generations and usually many generations must elapse for marked change to occur. Thus genetic inertia tends to perpetuate Pleistocene characters in the flora and probably in the fauna as well. An example of this may be the persistence of conspicuously thorned trees such as Hawthorns (Cratægus), Honey Locust (Gleditsia tricanthos (, native crabapple (e.g. Pyrus coronaria) and other thorned species. Add to this the persistence of certain fruits such as that of Osage Orange (Maclura pomifera). The fruit is a large, hard syncarp that is consumed by few animals but horses. While osage orange is native to the South-central US rather than the Central Appalachians it has been widely planted and escaped here.
It is likely that the large thorns and fruits of the cited trees were originally defense from and food for the greater browsing megafauna that ranged eastern North America during the Pleistocene (Mueller, 1990). This conclusion is supported by the fact that since the demise of the megafauna the only significant browser of eastern North America, where the most species of thorned trees occur, has since megafaunal times been the White-tailed Deer. Other large ungulates such as Bison (Bison bison) and the Elk (Cervus canadensis) which were also native to the region are essentially grazers.
The White-tailed Deer experiences little difficulty browsing between the large thorns such as those of the hawthorns or Honeylocust. On the other hand, the megafauna, the Ground Sloths, Mastodonts and other large browsers (Guilday, 1984) would have had great difficulty with the thorns. In addition the “monkeypuzzles” of large branching thorns which grow from the trunks of thorned trees, in combination with the widely spreading branches characteristic of these trees, would have also thwarted any Mastodont attempting to strip bark from the lower trunk.
The genetic inertia which perpetuates such structures as thorns for long after the selection agent has vanished can be explained in some species of hawthorns. These trees are known to seed by apomixis or the production of seeds without fertilization, which is analogous to cloning. For such plants the genetic variation required to adjust to new conditions is more limited than for species which utilize cross fertilization.
Among the conspicuously thorned trees the hawthorns are most widespread in the Central Appalachians. Unlike the Honey Locust, which is almost confined to rich bottomlands, one or the other of the many hawthorn species is found in virtually every mountain habitat. Although characteristically trees of openings, hawthorns frequently appear in the understory of mature deciduous forests if these forests are not too acidic. Others are found on the most exposed mountain peaks among summit rocks. One species, the Dotted Thorn (Cratægus punctata) is the characteristic species in the high elevation glades and among the spruce groves of the Allegheny Mountains.
The lesson here is that the Central Appalachian forest appears to contain living artifacts of the past. The full extent of this phenomenon and its significance can only be guessed. Artifacts which are visible, such as thorns or fruit, may presage a multitude which are not so obvious. Many of the characters yet to be recognized may be chemical. If thorns were required to repel Mastodonts then why not toxins, which like thorns have outlived their intended victims but are still part of the living forest?
Forest Stability and Equilibrium
Discussions of forest equilibrium are generally confined to presumed climax stands. However, the writer (Mueller, 2000 and above) has postulated that the concept may be generalized to include fundamental stability relations between vegetation, substrate, climate and other environmental factors at any stage of development or succession. In this stability field analysis plant species are regarded as occupying stability fields or volumes in multicomponental space (hyperspace) and communities are regarded as consisting of overlapping fields of the component species in this space. This system is based on an analogy with mineral-or quite generally with chemical-systems. Although these chemical system relations are thermodynamic in nature, and biologic systems are far too complex for this, the latter nontheless have their foundation in energetics as well.
An important practical point here is the function of stable communities as reference states in the study of forest succession and change in general. For example it is virtually meaningless to draw conclusions about succession from the absence of certain species in either undisturbed or disturbed forest without knowledge of the stability relations of these species. For example, the restricted occurrence of certain species may be related to the scarcity of the proper microhabitats rather than any successional stage. Even a cursory survey of the literature shows that these factors are seldom taken into account in the many studies of forest succession currently undertaken.
Usually climax forests are regarded as being in equilibrium unless there is evidence of instability. Braun (1950) discussed some criteria for forest equilibrium (climax). Those mentioned are (1) accordance of canopy and understory, (2) tendency of the same climax to develop as the result of unlike succession, (3) the occupation of topographically mature sites, (4) equilibrium between soil and occupying vegetation and (5) climax similarity over a large area. Of these point (3) is clearly in error since a climax may be developed on topography as new as glacial moraines. Also point (1) needs qualification. First reproduction in areas in which the canopy has been opened up may temporarily be quite different from the overstory. Also in some cases concordance is neither necessary (Chestnut Oak seedlings under Chestnut Oak canopy) nor sufficient (aspen sprouts under aspen) to establish equilibrium. However in the case of tolerant seedlings and saplings under mature trees of the same species as evidence may be compelling. In general however Braun’s ideas are in agreement with the definition of dynamic equilibrium.
The data of Delcourt and Delcourt (1993) suggest that biotic responses have approached dynamic equilibrium in the Central Appalachians beginning about 8000 years before present for cool temperate deciduous forests but that the mixed conifer-northern hardwoods north of 44° N latitude have not attained this state even today. Of course this conclusion addresses a more or less crude equilibrium that ignores minor forest migrations associated with temperature fluctuations, particularly around 7000 years ago. If this conclusion of broad equilibrium on a geographic scale is adopted, it follows that elevational zoning is also evidence of equilibrium since it recapitulates, with modifications, the latitudinal zonation. As previously indicated, where disturbances (primarily anthropogenic) have intruded, as in the Allegheny spruce forests, the tendency is for the forest to return to the equilibrium type. These conclusions are in general agreement with Braun’s criteria 2,4 and 5 as well as the general concept of equilibrium.
It should be mentioned that the large scale equilibrium exemplified by forest climax as discussed above is merely a manifestation of the same energetic factors at work on a microhabitat scale as proposed in our stability field analysis and which applies to the flora of any stage of succession.
Old growth is the touchstone of ecological forestry. Foresters who fail to recognize its importance can only claim to be industrial woodcutters. Zahner (1989) gave the following simple definition: “Old Growth forests are forests having a long uninterrupted period of development.” Note that this definition says nothing about the ages of individual trees but does say a great deal about their habitat. This definition fits the Central Appalachians well because, while easily identifiable old growth with obviously old, large trees, is scarce, there are many stands seemingly undisturbed by humans, that may qualify despite a scarcity of old trees. In many forest types — cove, mixed mesophyte, northern hardwood, spruce montane as well as many dry oak forests there are large old trees and many are still being discovered. One such stand was recently found in cutting unit one of the Stillhouse Timber Sale on Shenandoah Mountain, a fact that the George Washington National Forest had attempted to conceal. However in the dryest oak-chestnut and oak-pine forests on inaccessible ridges we find ambiguity. Many such areas had burned frequently in the past. Thus although, except for the loss of chestnut, such stands may be primary and even virgin forests, they may contain few old trees and so are difficult to distinguish from stands disturbed by humans.
The ages of tree species have considerable significance with respect to their classification by industrial foresters. For example, the US Forest Service regularly twists normal tree mortality data to justify timber sales. They attempt to conceal that, as a healthy forest matures, most, indeed more than 99 percent, of its trees must die before it reaches maturity, to say nothing of old growth. And this mortality is entirely independent of species longevity. Most of this mortality occurs while the forest is still young. Industrial foresters would have us believe that 80-90 year old stands are “decadent,” “overmature” or “falling apart” because they contain dead trees. In this distortion they ignore their own literature (e.g. Fowells, 1965) which gives the following commonly attained ages for eastern forest trees: White Oak 600 years, Northern Red Oak 200-300 years, Black Oak 200 years, Sugar Maple 400 years, American Beech more than 360 years, White Pine 450 years and Canadian Hemlock 900 years. These data show that survivors in a healthy maturing forest have the capability of attaining far greater ages and larger sizes than those classified as mature by industrial foresters.
The greatest significance of old growth lies in the now-rare habitat niches it contains. Features such as large standing (frequently hollow) snags, abundant large woody debris, stream debris dams, pit and mound topography and canopy gaps that result from large tree falls are some of the criteria for old growth. Edaphic megapores, large elongated openings in soils due to root decay or burrowing by animals, have been stressed by Martin (1992) in his discussion of old growth mixed mesophyte forests.7 Such features combine to form a complex horizontal and vertical structure that can accommodate a great diversity of sensitive forest interior species. Examples include most salamanders, small mammals, neotropical migrant birds, and large raptors like the Coopers Hawk. Old growth also hosts abundant arthropods; some, like the millipedes, striking in appearance, some endemics (Hoffman, 1991).
The animals of the Central Appalachian forest are of no less consequence than its grandest trees. They, in truth, are the forest as much as the trees are. In these forests all life forms, plants, animals, fungi, the micro flora-and-fauna, are not only linked together in the dance of life but actually emerge from each other in time. Look at the forest scene —does it seem complex or chaotic in the placement of trees, in the shape of limbs and the riot of plants on the forest floor? Look again—and again—and the longer you look the more order will appear. Each twist of a limb has meaning in terms of light and wind history. Genetic adaptability calls forth thickened bark on the lower side of leaning trunks to guard against fire, which burns hottest there. Moss does grow preferentially on the north side of trees, but not blindly. It always calculates modifying factors like the shade of neighboring cliffs. Each nuance of leaf form, texture and chemical make-up potentially reflects a response to every insect, pathogen or browser the tree has encountered in its long evolutionary history. We have already seen that there is a fossil linkage between many of today’s trees and the great browsing fauna that lived 15,000 years ago. Similar relations are being forged today.
During the last 15,000 years Central Appalachian forests as well as the rest of North America experienced two great episodes of faunal decline. The first of these was the wave of extinctions as the ice age ended. The second is on-going extinction and extirpation associated with the coming and settlement of Europeans as well as modern development. Unfortunately after partial recovery of our forests from the original onslaught of the settlement period extinction and extirpation are again on the rise and may soon eclipse all species losses of the past.
In our forests birds are the most conspicuous animal life form. We may only catch occasional glimpses of them but their songs are seldom absent. In these songs order is again manifest, not only in the characteristic phrasing of each species but in what time of day and where in the forest they are heard, whether at low or high elevation, in dry or moist habitat and in which level of canopy. Throughout the Central Appalachian deciduous forests and during most of the summer several species make us aware of their presence by their highly distinctive calls. Almost omnipresent and most persistent are the vireos and especially the Red-eyed Vireo. (Vireo olivaceous) with its truncated Robin-like song. Another is the Scarlet Tanager (Piranga olivacea), and although its striking red and black plumage is usually hidden in the tree tops, its voice —like a Robin with laryngitis—is unmistakable. The third member of this conspicuous group is the Wood Thrush (Hylocichla mustelina). This bird is usually on or near the forest floor and its flute-like song, once heard, will always conjure up the occasion of the first experience. The calls of this group of birds are low enough in pitch to be heard by almost everyone but there is a host of small songsters, among which wood warblers dominate, which in many cases have such high pitched songs as to challenge some ears. These small birds also tend to move fast in secretive ways. There are of course many larger birds that we encounter less frequently than tanagers or Wood Thrushes. One is the Yellow-billed Cuckoo (Coccyzus americanus) which is heard most frequently on rainy days. Another is the Pileated Woodpecker (Dryocopus pileatus), crow-sized with a flaming red crest and a loud staccato call not too different from that of a Coopers Hawk. This woodpecker seems to thrive in the Appalachians, perhaps because of the frequency of ice storms ensures a supply of broken trees and hence a ready diet of wood borers.
When we climb to higher elevations, there is a change in forest type. Above 3500 ft. asl throughout the Central Appalachians we are likely to see the Wood Thrush replaced by its relative the Veery (Catharus fuscescens) and more rarely by Swainson's Thrush (Catharus ustulatus) or the Hermit Thrush (Catharus guttatus). The ethereal, wavy descending call of the Veery may, for example, be heard in Red Oak forests along of the spine of Shenandoah Mountain or the Virginia/West Virginia border while Swainson's and Hermit Thrushes are most at home in the Allegheny Spruce belt. Also at these elevations, but some times much lower, we encounter the Rose-breasted Grosbeak (Pheucticus ludovicianus) with its more elegant-than-a-Robin, Robin-like call, and bright plumage. At night and on many dark days the airy bird voices of day are replaced by the louder and more mysterious calls of owls and Whip-poor-wills (Caprimulgus vociferus). Among the owls, which number three common and several rare species in these forests, the Barred Owl (Strix varica) is by far the most conspicuous in most forest types. Its boisterous and varied hooting is probably the most impressive animal night sound. However a close second is that of the Whip-poor-will, a member of the Nightjar family. In the quiet forest night the endless repetition of its name by this bird transcends what might be irritation in another sound and instead leaves one reassured of nature’s vitality.
In the more restricted realm of the coniferous forest we find a number of birds that not only form an extension of the boreal fauna but are closely dependent on conifer seeds. The Red Crossbill (Loxia curvirostra) is a small but conspicuous inhabitant of the Allegheny spruce belt and the pine heaths that occur on some of the highest elevations of the Valley and Ridge and Blue Ridge provinces. It is dependent on Red Spruce or, in the Valley and Ridge, on Pitch Pine and Table Mountain Pines for most of its food and nesting habitat. On June 19, 1984 I observed two males of this species singing competitively on the very tops of two spruce trees. This occurred near the summit of Spruce knob, the highest point in West Virginia. Veeries were heard singing in the same area. Another similar bird of reddish plumage that depends on these conifers is the Purple Finch (Carpodacus purpureus). It may also be seen in large flocks in other parts of the forest during spring migration. Space limits discussion of all the northern bird species that extend their ranges south along the Appalachians. However two more yet merit our attention. They are the Northern Raven (Corvus corax) and the Northern Goshawk (Accipiter gentilis), both circumpolar species. Although a disjunct population, the Northern Raven thrives and may be seen in all parts of these mountains. It is the dominant corvid in the mountains proper but suffers harassment by crows in the agricultural valleys. By contrast the Goshawk is rare and confined to the most remote locations. It is however extending its range southward.
From an ecological standpoint birds are rapid and convenient indicators of forest richness or the quantity of nutrients in the food chain. This soon becomes apparent in any lengthy traverse. For example, in the dry oak-chestnut type forest calls and other evidence of birds will be few but as one approaches a cove or riparian zone all these signs increase greatly. The highest densities of birds of most kinds probably occur along streams such as the South Branch of the Potomac or those of the Shenandoah Valley all of which flow through regions of carbonate rocks.
John Terborgh (1990) and other have noted marked declines of songbirds in eastern North America. For this reason it is desirable to keep records on all possible species encountered. One salient reason for decline in our region that presents itself for continuous observation is the great abundance of certain birds — crows, grackles, etc. — that flourish in our agricultural valleys and which are known predators of eggs and nestlings. These predatory hoards are not only active in the Valleys but also far out into the surrounding mountains. It is likely that they are a major source of songbird decline even in some of the remotest forest regions.
While birds are the most conspicuous fauna of the Central Appalachians, arthropods, and especially insects, interact far more pervasively with the vegetation. The role of such species as the Gypsy Moth and Pine Beetles as major forest disturbances has already been discussed. But disturbances tend to be episodic and species which play a continuous part may be of even greater consequence. An example is the nutrient recycling done by minute soil arthropods such as springtails (Collembola), mites (Acarina) and others that may reach population levels of many thousands in each square meter of the forest floor. George W. Byers has devoted 32 years to the study of these organisms at the Mountain Lake Biological Station in Virginia’s Valley and Ridge (Byers, 1994) where he has found no significant decline or increase in numbers during that time. The forest studied is an undisturbed, although second growth, high elevation oak forest. It is possible that the maturation of this forest compensates for such factors as increases in air pollution.
Like the bird life Central Appalachian insects include a number of disjunct northerners. Among Butterflies are counted the rare Tawny Crescent (Phyciodes batesi) and the Pink-edged sulfur (Colias interior), an inhabitant of high elevation heaths where its larvæ feed on Blueberry leaves. Also included in this group are a number of Damselflies (Roble, 1994) which inhabit mountain glades and wetlands. Some, like Enallagma cyathigerum have a circumpolar distribution.
In addition to disjunct northern species the Central Appalachians are extraordinarily rich in native Butterflies. Milkweed plants (Asclepias spp.) in forest openings may attract swarms of Great Spangled Fritillaries (Speyeria cybele) and along deep forest trails one can on occasion sight the strikingly patterned male Diana (Speyeria diana). Almost equally colorful are the large millipedes that creep among the leaves, especially in the rich cove forests. According to Hoffman (1991) a number of these arthropods are endemic to restricted localities. Occasionally surprises are encountered as in late July 1994 in the deep valley of Skidmore Fork that divides the Shenandoah Range. Here we were assailed by clouds of tiny biting yellow insects that appeared to be thrips rather than the expected flies. Could it be that they mistook us for vegetation and the biting was random? Thrips almost invariably suck plant juices. Complementing these terrestrial arthropods are numerous aquatic species that inhabit the mountain streams, ponds and other wetlands. These include but are not limited to amphipods, isopods, mayflies, dragonflies and stoneflies.
Perhaps the vertebrates most closely tied to the forest environment are the amphibians, the toads, frogs and salamanders that inhabit the forest floor and forested and open wetlands. Around a dozen species of toads and frogs (anurans) and 20 salamanders occur in the region (Smith, 1978). Given the apparent worldwide decline in amphibian numbers and little available baseline data, it is difficult to say with confidence what the health of our amphibian populations is. We do have evidence that many species suffered serious declines and probably some extinctions due to past and ongoing settlement, logging and development stresses. I have frequently been struck by the absence in the Central Appalachians of the swarms of frogs (northern Leopard in this case) that I remember from my Wisconsin childhood. Yet there are selected areas in these forests where frogs are abundant. This is especially apparent along the seeps, streams and sinkholes at the western base of the Blue Ridge. In this relatively acid environment the species are mostly tiny Cricket and other Tree Frogs. But larger species are also present. Other species frequently noted are the Mountain Chorus Frog (Pseudacris brachyphona), as in the high elevation pond on Potts Mountain, and the Pickerel Frog (Rana palustris) in mainly acid seeps. The most frequently encountered species in dry upland forests far removed from water is the Wood Frog (Rana sylvatica). In circumneutral waters of limestone valleys the Bullfrog (Rana catesbyrania) and the Green Frog (Rana clamitans), which are more demanding of habitat, are usually present if not abundant. Thankfully almost everywhere, where there is standing water, we can still hear the melodic piping of the Peeper Tree Frog (Hyla crucifex) soon after ice breaks in spring.
Salamanders have a unique place in the food chain since they are by life habit, adapted to feeding upon the abundant soil fauna such as springtails as well as other animals of the forest floor. They are in turn fed upon by birds and larger animals who bring nutrients to the top of the chain. Salamanders fall into a number of family groupings. Among the mole salamanders the Tiger Salamander (Ambystoma tirgrinum), the largest terrestrial salamander, occurs as a disjunct population, again in the unusual aquatic habitat of sinkholes and seeps at the base of the Blue Ridge. The most abundant salamanders both as species and individuals are the lungless forms. Some lungless salamanders are, like mole salamanders, dependent on water bodies. However the largest lungless group, the Woodland Salamanders, are liberated from this requirement and lay their eggs in nests on the forest floor or under rocks or debris. Of this group the genus Plethodon is the most widespread and the Red-backed Salamander (Plethodon cinereus) is probably the most common salamander in the region. Plethodons are known for their restricted mobility and many are confined to a few square meters all their lives. Their numbers may exceed 5000 per hectare (Burger, 1935) and it has been estimated that salamanders represent the greatest concentration of vertebrate biomass in these forests.
Four Plethodons in the Central Appalachians have some of the most restricted ranges of any salamanders. They are the Cheat Mountain (Plethodon netlingi), the Cowknob (P. punctatus), the Shenandoah (P. shenandoah) and the Peaks of Otter (P. hubrichti) Salamanders. Of these the first three occur at the highest elevations but their original ranges may once have extended lower. The Shenandoah Salamander is the rarest of the four and is listed as Endangered under the ESA. It is confined to north and northwest facing talus slopes of Stony Man, The Pinnacle and Hawksbill Mountains in a small area of Shenandoah National Park and is a severe competition with the Red-backed Salamander. The Cheat Mountain Salamander is confined to scattered populations in high elevation spruce and northern hardwood forests of the Allegheny spruce belt. It is listed as Threatened under the ESA and like the Shenandoah Salamander is in competition with the Red-backed and other common salamanders. Both the Cowknob and Peaks of Otter Salamanders are Category 2 under the ESA but possess larger ranges than the other two salamanders. They occur in deciduous forests, and in the case of the Cow Knob Salamander, mostly in the high elevation Northern Red Oak zone However the Cow Knob is also found as low as 735 meters (2410 feet) asl and may have occupied a much larger range before the mountains were logged at lower elevations. Pauley (1993) has studied the Cheat Mountain Salamander extensively and summarized the results. Summaries of studies of the Shenandoah Salamander (Wynn, 1991), the Cowknob Salamander (Pague, Buhlmann, and Mitchell, 1991) and the Peaks of Otter Salamander (Pague and Mitchell, 1991) are contained in the book Virginia’s Endangered Species.
There are three interesting salamanders without which our discussion would be incomplete. The giant aquatic Hellbender (Cryptobranchus alleganiensis) inhabits clear, rocky headwaters of the Ohio and Tennessee drainage and reaches 740 mm (29 inches) in length. The Green Salamander (Aneides aeneus) is the only salamander north of Mexico with extensive green coloring and is the only climbing salamander in the eastern U.S. and Canada. Perhaps the most familiar of all salamanders in the region is the Eastern Newt (Notophthalmus viridescens). Although it breeds in water this salamander has an “eft” stage which spends one to three years on land. Efts are brilliant orange-red in color as a warning to birds of their toxicity and thus stand out clearly on the forest floor. They are also quite mobile and resistant to drying and are frequently encountered particularly in rich woods, throughout the summer and into fall.
In Central Appalachian forests reptiles are chiefly snakes and turtles since the cool, humid climate does not favor lizards. Snakes number perhaps a dozen non-poisonous species and two poisonous. Among the former perhaps the most frequently seen, at least at lower elevations, is the Rat or “Black” Snake (Elaphe obsoleta), a large (up to 250 cm) constrictor capable of killing large birds and an excellent climber. Around streams the Northern Watersnake (Nerodia sipedon) is frequently encountered. Among smaller snakes the Garter Snake is most common but two elegant little green snakes stand out. They are the rough Green Snake (Opheodrys æstivus), of low to moderate elevations, and the Smooth Green Snake (Opheodrys vernalis) found in high elevation glades. Poisonous snakes are represented by the Forest Rattler (Crotalus horridus) a beautiful snake in either brilliant yellow or almost black color phases that can lend excitement to a mountain hike when suddenly encountered. Less flamboyant and more secretive is the Copperhead (Agkistrodon contortrix). Care should be taken to avoid either species.
Among turtles the Eastern Box Turtle (Terrapene carolina) is by far the most commonly encountered species in upland forests and is present in fens and other wetlands as well. More closely dependent on water as semi-aquatic species are the Wood Turtle (Clemmys insculpta) and the Bog Turtle (C. muhlenbergi). Both have suffered greatly from loss of habitat and collecting. The Bog Turtle in particular is very rare and is Category 2 under the ESA. In productive wetlands and streams the large aquatic Snapping Turtle (Chelydra serpentina) may be abundant. Although closely tied to swamps or marshes most of the year it seeks nearby uplands to lay its eggs and undertakes extensive migrations between watersheds. It does this during rainy periods when it may sometimes be seen excavating temporary mud wallows on high ridges as it pauses in its wanderings. Only a few lizards find suitable habitat in the Central Appalachians. One is the small, inconspicuous Coal Skink (Eumeces anthracinus), an occupant of the forest floor at lower and moderate elevations. Far more impressive is the Broadhead Skink (E. laticeps) which favors wooded wetlands. I was startled by one of these large lizards in late May as I approached the shore of one of the sinkhole ponds at the base of the Blue Ridge. A male with a bright red head — the breeding coloration— emerged from the water with a splash and dashed up a dead snag — certainly a fitting complement to a day of botanizing. However the species as well as suitable habitat is rare in these mountains and confined to a few low elevation water-rich sites.
Some of our largest and wide-ranging mammals were extirpated since Europeans overran the region. These included the Gray Wolf, Bison and Elk or Wapiti. In addition some smaller wilderness carnivores such as the Fisher (Martes pennanti) and the Pine Martin (Martes americana) disappeared with the virgin forests. The status of the Eastern Cougar (Felis concolor couguar) is still regarded as uncertain despite numerous reports of sightings of cougars of some kind. The Porcupine (Erethizon dorsatum) once ranged the spruce belt and northern hardwoods of the Allegheny Plateau and undoubtedly into the valley and ridge as well. Although regarded as extirpated, “vagrant” Porcupines still turn up in the region (Handley, 1991) and the species may be recovering as suitable habitat regenerates. The animal’s only predator and nemesis is the Fisher, which has recently been reintroduced, already awaits its return.
Although many of the larger animals native to the Central Appalachians suffered extinction or extirpation during the last 15,000 years, a number of smaller species which are really holdovers from the ice age still survive. Examples are the Varying or Snowshoe Hare (Lepus americanus), the Northern Flying Squirrel (Glaucomys sabrinus fuscus), the Rock Vole (Microtus chrotorrhinus carolinensis) and the Water Shrew (Sorex palustris). The Varying Hare is closely associated with Red Spruce forests as is the Northern Flying Squirrel, while the Rock Vole and Water Shrew live along high elevation rock slides and streams respectively. More widespread but in similar habitat as the Rock Vole is the Eastern Woodrat (Neotoma floridana). Some students of these two animals in Pleistocene deposits (e.g. Graham and Lundelius, 1984) regard their association “disharmonious” since the Rock Vole is northern species whereas the Wood Rat has a decidedly southern distribution.
Large mammals that still occur in all Central Appalachian forest types are species that have wide ranges in latitude and longitude. They include the Black Bear (Ursus americanus), the White-tailed Deer (Odocoileus virginianus), the Bobcat (Lynx rufus), the Coyote (Canis latrans) and the Beaver (Castor canadensis). The Beaver is of course dependent on the presence of bodies of water and suitable food plants. The Black Bear depends on abundant food- usually nuts and berries- to fatten for winter. It also requires mud wallows, so that the isolated and scattered wetlands of these mountains form an important part of habitat for this animal. It is widely recognized now that in most part of the Central Appalachians White-tailed Deer populations exceed carrying capacity. This is shown particularly in overbrowsing of certain plants — such as the Canada Yew for example— to the extent that they are being extirpated over large areas. Another emerging consequence of this overpopulation is the spread of Chronic Wasting Disease (Transmissible Spongiform Encephalopathy) in White-tailed Deer (information widely available on the internet). This disease, which is similar to Mad Cow Disease, is rampant in the West and Midwest and will likely spread to the East, given the continuum of overpopulated Deer herds linking the areas.
Bobcats are always secretive but are powerful predators in their own right. They may weigh 40 lbs. in these mountains and are able to prey on small deer. The Coyote appears to be a late arrival from the West and has been increasing in numbers. This small wolf preys on small animals including deer fawns. The Beaver has a special role in that it diversified habitat through its pond construction and tree felling. Since the Beaver has only recently been making a comeback, after virtual extirpation, it has not yet built up a full complement of its successional habitat types in the region. In the future this succession will result in many new wetland and grassy openings as well as new stands of moisture loving forest types.
A group of wide-ranging and very adaptable small mammals today play a more important role in forest ecology than in the past. They are the Opossum (Didelphis virginiana), the Raccoon (Procyon lotor), the Striped Skunk (Mephetis mephetis) and the Gray Fox (Urocyon cinereoargenteus) All have benefited from the activities of humans and are adapted to forest edges and openings. Although technically carnivores all are really omnivores. Humans have favored these animals first by eliminating the large carnivores, the wolves and Cougars, that once preyed upon them. Secondly they benefit from the bountiful food, animal and vegetable, available from agricultural activities in the mountain valleys. It is a benefit they share with the local crows and Jays, and the numerous grackles and blackbirds. The result is an increase in numbers of both animal and bird predators, numbers that then fan out into the surrounding mountains to prey on increasingly vulnerable forest interior birds, amphibians and reptiles. The creation of openings in the mountain forests only exacerbates this situation as do the “wildlife” management activities of the public agencies.
Two groups of mammals that are more a part of the forest than most are the squirrels and bats. The Northern Flying Squirrel previously discussed has a more widespread low elevation counterpart, the Southern Flying Squirrel (Glaucomys volans). Far more conspicuous than these small nocturnal animals however is the Eastern Gray Squirrel (Sciurus carolinensis) and the more robust Eastern Fox Squirrel (Sciurus niger). These squirrels show great variation in local populations as a function of soil fertility since they depend primarily on nut crops. They are most abundant —as shown by nest frequencies— in hickory forests of the limestone regions where there may be several nests per acre. By contrast, dry oak forests may show few signs of squirrels even when acorns are abundant.
Less common at low elevations than Gray and Fox Squirrels but increasing in numbers with elevation is the small but aggressive Red Squirrel (Tamiasciurus hudsonicus). Like the Northern Flying Squirrel it is well adapted to spruce forests.
More than a dozen bat species are summer residents of the Central Appalachians. All are closely tied to forests, a fact unfortunately not appreciated by forest managers. There is much concern for the preservation of cave habitat for bats, a habitat some utilize year round and others only for hibernation. In the Central Appalachians, all caves are inextricably linked to forests. Only forest cover in the cave vicinity can reliably provide the steadiness of air flow, moisture content and quality for optimum cave conditions. Similarly only isolation or protection from vandals can prevent the destruction of cave habitat that has become an epidemic. However bats do not live by caves alone. They spend much of their time foraging, mostly in forests, although this includes forest openings particularly in wetlands and along streams. Some bats also rear their young in the forest. The rare Indiana Bat (Myotis sodalis) forms maternity colonies of up to 90 females under the lose bark of large Shagbark Hickories, White Oaks and other trees (Dalton and Handley, 1991). The benefit of old growth forest to this species, which is listed as Endangered under the ESA, is thus clear.
Many of the forest animals discussed here suffer from forest fragmentation. Among all species the need to move to seek new habitat to exchange genetic material between metapopulations and particularly as a response to disturbances, should be clear to every one. As mentioned earlier, even highly aquatic species such as Snapping Turtles and frogs need to move between aquatic habitats. Although some species such as woodland salamanders may be virtually confined to a few square meters of forest floor throughout their lives they still must move to re-colonize adjacent disturbed areas. These salamanders are thwarted in this by even relatively narrow woods roads if these have beds of dry soil or rock. Even such mobile small mammals as squirrels need to migrate when nut crops fail locally. Wide paved roads hinder such movements and expose them to increased mortality in a number of ways.
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1 Fruit orchardists know this form to be most stable in bearing heavy loads of fruit.
2 This plant is considered rare even on the Allegheny Plateau
3 These and a number of other rare plants were identified by Dr. Robert Hunsucker (Hunsucker and Mueller,1998).
4 I use this term to distinguish such assemblages from mixed forest.
5 An excellent example of this differential effect of fire may be seen on the mountainside just east of the Hone Quarry Campground in the Dry River Ranger District of the George Washington National Forest.
6 Many trees also have quite subtle fire adapted or resistant characteristics. These take the form of rock accumulation rings concentric about the tree base that build up by diameter growth as well as greatly thickened bark on the lower and hence most fire-exposed sides of leaning trunks.
7 Most of these features are present in the stand of large Chestnut and White Oaks of the proposed Stillhouse Timber Sale mentioned earlier. In addition a complex fire history is displayed in this stand.