Northern hardwood forest

Distinguishing Features

Northern hardwood forest can be distinguished from other high elevation forest types by the dominance of mesophytic canopy trees (American beech, yellow birch, yellow buckeye, and sugar maple) since other high mountain forest types generally have northern red oak, red spruce, or Fraser fir as canopy dominants.

Introduction

Northern hardwood forest occurs on medium- to high-elevation (generally over 4,000 ft.) slopes, coves, and flats, often on north-facing slopes. The soil is usually moist, due to high rainfall and low temperatures. The relatively large trees form a dense forest except on exposed high-elevation sites where trees are dwarfed and the forest is more open. The broad-leaved deciduous trees that dominate northern hardwood forest contrast with the needle-leaved evergreens of spruce-fir forest. Perhaps the most striking feature of northern hardwood forest is its brilliant display of autumn colors. The autumn air is clearer and cooler than in summer and at no other time of year is the rich array of trees more apparent.

Vegetation

Mesophytic (moisture-loving) trees, primarily American beech (Fagus grandifolia), yellow birch (Betula alleghaniensis), yellow buckeye (Aesculus flava), and sugar maple (Acer saccharum) dominate the canopy. Other canopy species include white basswood (Tilia americana), white ash (Fraxinus americana), and at higher elevations, red spruce (Picea rubens). Common understory trees include striped maple

(Acerpensylvanicum), mountain maple (Acer spicatum), and smooth serviceberry (Amelanchier laevis). Pipevine (Aristolochia macrophylla), a climbing vine with large heart-shaped leaves, is found on the edge and other well-lit areas of the forest. A sparse to fairly dense shrub layer includes witch hobble (Viburnum lantanoides), wild hydrangea (Hydrangea arborescens), and Appalachian gooseberry (Ribes ro-tundifolium). The herbaceous layer is often dense and quite diverse, particularly on sheltered sites with deep, moist soils. Common herbs include false Solomon's seal (Maianthemum racemosum), blue cohosh (Caulophyllum thalictroides), Curtis's goldenrod (Solidago curtisii), wake robin (Trillium erectum), and large-flowered bellwort (Uvulariagrandiflora). Scattered patches of mosses and lichens are easily overlooked, except in winter, when plants in the other layers have died back and the forest floor is mostly a drab brown. Along streams and seepage areas, plant cover can be lush with characteristic species such as flowering raspberry (Rubus odoratus), umbrella leaf (Diphylleia cymosa), and crimson bee balm (Monarda didyma). Almost all herbaceous plants in mountain forests are long-lived perennials that store nutrients in autumn in underground rhizomes, bulbs, or roots that provide the resources needed for resprouting in spring. Fringed phacelia (Phacelia fimbriata) and yellow jewelweed (Impatienspallida) are unusual in that they are short-lived (annual) plants that regenerate from seed each year.

BEECH GAP FOREST

A variant of northern hardwood forest called beech gap forest occurs primarily in gaps and ridgetops at elevations greater than 4,500 ft., where trees are exposed to desiccating winds, frequent low temperatures, and ice storms. The severe climatic conditions result in canopy trees that are stunted and have a distinctly gnarled appearance. Despite their small size, the canopy trees are often quite old. The canopy is dominated by American beech with lesser amounts of yellow buckeye and yellow birch. There is little or no subcanopy or shrub layer, but the herbaceous layer can be very dense. Common herbs include Pennsylvania sedge (Carex pen-sylvanica), white snakeroot (Ageratina altissima), black cohosh (Actaea racemosa), hayscented fern (Dennstaedtiapunctilobula), and beechdrops (Epifagus virginiana), a flowering plant that is a root parasite on American beech. Beech gaps occur in small patches surrounded by other high-elevation forest types and by grassy or heath balds.

Seasonal Aspects

Seen from afar, the white flower clusters of smooth serviceberry resemble white clouds against a mostly leafless forest in early spring. Another early blooming species is yellow buckeye — bumblebees and hummingbirds seeking energy in the form of its sugar-rich nectar actively visit and pollinate its yellow tubular flowers. Wind-pollinated trees such as American beech, yellow birch, and sugar maple release enormous amounts of pollen from relatively inconspicuous flowers in spring. Striped maple differs from most maples in that its small, bell-shaped, nectar-producing flowers are pollinated by insects (small bees and flies), rather than by the wind.

The dense mats of the white to pink flowers of Carolina spring beauty (Clay-tonia caroliniana) produce spectacular displays in early spring. Fringed phacelia also forms colorful patches in spring—its numerous small white flowers collectively resemble a light cover of newly fallen snow. Wake robin produces maroon or white flowers on upright stalks whose fetid odor attracts flies and beetles that function as pollinators. Queen bumblebees pollinate the limp (even when fresh), nodding butter-yellow flowers of the large-flowered bellwort. Other plants to observe in spring include the white lacy flowers at the tips of the arching stems of false Solomon's seal, and umbrella leaf's white flowers on stalks above pairs of large umbrella-shaped leaves.

In spite of its common name, hummingbirds (not bees) pollinate the bright-red tubular flowers of crimson bee balm. Other summer-flowering woodland herbs include black cohosh, white snakeroot, yellowjewelweed, and wood nettle (Laportea canadensis). The numerous white stamens within each black cohosh flower give its long, narrow inflorescences a fuzzy white appearance. White snakeroot's white flower heads at the tips of leafy shoots also have a fuzzy look. Bumblebees frequently visit yellow jewelweed's flowers to obtain nectar from the down-curved nectar spur. Touching the narrow, elongate ripe fruits of jewelweed causes them to explode, thereby dispersing the seeds. Touching wood nettle's hairy foliage is less fun, as a stinging sensation lasts for several minutes.

Wild raspberry produces showy, deep pink to purple bowl-shaped flowers in summer that mature into fleshy red fruits. In summer and fall, pipevine swallowtail caterpillars (black with reddish spots) can be seen feeding on the large heart-shaped leaves of Dutchman's pipe, a woody climbing vine whose flowers resemble an old-fashioned smoking pipe. Red squirrels feed on the winged seeds of sugar maple, as well as on the sweet sap oozing from stem wounds. Because goldenrods typically occur in fields and roadsides, you may be surprised to discover Curtis's goldenrod in the forest understory—its yellow flower heads occur in small clusters within the upper leaf axils in late summer and fall.

Distribution

Northern hardwood forest is restricted to the southern Appalachians of western North Carolina, eastern Tennessee, southwestern Virginia, and, less frequently, northeastern Georgia. A similar forest type in the northeastern United States has significantly fewer species due to the species loss caused by Pleistocene glaciers. On more sheltered slopes, "bowls," and upper coves, the boundaries between northern hardwood forest and rich cove forest, are often blurred as they share many of the same species and as the transition between community types can be gradual.

Dynamics

High winds and ice storms create openings in the forest canopy, providing an opportunity for new trees to get established and releasing shade-suppressed saplings. The large number of broken branches on the forest floor and scattered downed trees reflect frequent wind and ice damage. Fires occur infrequently due to moist conditions; however, fires can be quite damaging during drought periods as many trees in this forest have relatively thin bark. Clusters of opportunistic species such as yellow birch, fire cherry (Prunuspensylvanica), and black locust (Robiniapseudoacacia) are good indicators of past logging or fires.

European wild boars impact vegetation. This species, like wild pigs everywhere, eats just about anything it can find, including acorns, hickory nuts, beechnuts, tubers, and bulbs. Wild boars also eat, uproot, and trample wildflowers such as spring beauty, trout lily, and trillium and damage tree roots, seedlings, and saplings. They tear up rhododendron thickets, dig up sod on grassy balds, pollute streams, and compete with native animals for berries, acorns, and nuts. Because fruit availability fluctuates markedly from year to year, this competition can have serious consequences for native wildlife. The potential impact of wild boars is exacerbated by their high reproductive output. A female boar can produce 10 young per litter, whereas a female black bear, for example, normally produces 2 cubs every other year. While large numbers of wild boars have been trapped or shot, totally eliminating them is virtually impossible. Increasing numbers of wild boars, now in the thousands in the southern Appalachians, could substantially reduce populations of black bear, squirrels, and other wildlife, as well as significantly reduce the abundance and diversity of herbaceous plants.

Conservation Aspects

Northern hardwood forest is limited to higher-elevation sites (generally over 4,000 ft.) within the relatively small geographic area of western North Carolina, eastern Tennessee, southwestern Virginia, and northeastern Georgia. This community usually occurs on public lands administered by the U.S. Forest Service (e.g., Pisgah, Nantahala, Cherokee, Jefferson, and Chattahoochee National Forests) and the National Park Service (e.g., Great Smoky Mountains National Park, Shenandoah National Park, and the Blue Ridge Parkway) and are thought to be reasonably well protected at the present time. Threats include invasive species, disease, and air pollution. For example, grazing and soil disturbance by European wild boars have reduced herbaceous plant cover in beech gap forests by up to 90 percent. Beech bark disease, a complex made up of the beech scale insect and two closely associated fungi, has caused mortality of numerous American beech trees. High-elevation plant communities are particularly vulnerable to atmospheric deposition of air pollutants such as acid rain and ground-level ozone.

SUGGESTED READING

McLeod, D. E. 1988. Vegetation Patterns, Floristics and Environmental Relationships in the Black and Craggy Mountains. Ph.D. diss., University of North Carolina, Chapel Hill. Russell, N. 1953. The Beech Gaps of the Great Smoky Mountains. Ecology 34:366-74. White, P. S., E. Buckner, J. D. Pittillo, and C. V. Cogbill. 1993. High-Elevation Forests: Spruce-Fir Forests, Northern Hardwood Forests, and Associated Communities. In Martin, W. H., S. G. Boyce, A. C. Echternacht, eds., Biodiversity of the Southeastern United States: Upland Terrestrial Ccommunities, 305-38. New York: Wiley and Sons.

NORTHERN HARDWOOD FOREST: CHARACTERISTIC PLANTS

Trees

NORTHERN HARDWOOD FOREST: CHARACTERISTIC PLANTS

ABUNDANT SPECIES

Aesculus flava

Yellow buckeye

pp. 224-25

Betula alleghaniensis

Yellow birch

pp. 226-27

Fagus grandifolia

American beech

pp. 237-38

OCCASIONAL TO LOCALLY ABUNDANT SPECIES

Acer pensylvanicum

Striped maple

p. 221

Acer saccharum

Sugar maple

pp. 222-23

Acer spicatum

Mountain maple

pp. 223-24

Amelanchier laevis

Smooth serviceberry

pp. 225-26

Fraxinus americana

White ash

pp. 238-39

Magnolia acuminata

Cucumber tree

pp. 243-44

Picea rubens

Red spruce

p. 248

Tilia americana

White basswood

pp. 263-64

Shrubs and Woody Vines

OCCASIONAL TO LOCALLY ABUNDANT SPECIES

Aristolochia macrophylla

Pipevine, Dutchman's pipe

pp. 271-72

Cornus alternifolia

Alternate leaf dogwood

p. 279

Hydrangea arborescens

Wild hydrangea

p. 287

Rhododendron catawbiense

Catawba rhododendron

pp. 301-2

Ribes rotundifolium

Appalachian gooseberry

p. 308

Rubus allegheniensis

Allegheny blackberry

p. 310

Rubus odoratus

Flowering raspberry

p. 311

Sambucus racemosa

Red elderberry

p. 313

Viburnum lantanoides

Witch hobble, Hobblebush

p. 321

Herbs

ABUNDANT SPECIES

Ageratina altissima

White snakeroot

pp. 328-29

Dennstaedtia punctilobula

Hayscented fern

p. 360

Laportea canadensis

Wood nettle

p. 395

Maianthemum racemosum

False Solomon's seal

p. 401

Viola canadensis

Canada violet

pp. 465-66

OCCASIONAL TO LOCALLY ABUNDANT SPECIES

Actaea racemosa

Black cohosh, Bugbane

pp. 326-27

Arisaema triphyllum

Jack-in-the-pulpit

p. 335

Aruncus dioicus

Goat's beard

p. 336

Carex pensylvanica

Pennsylvania sedge

pp. 343-44

Caulophyllum thalictroides

Blue cohosh

pp. 345-46

Claytonia caroliniana

Carolina spring beauty

pp. 350-51

Diphylleia cymosa

Umbrella leaf

pp. 364-65

Epifagus virginiana

Beechdrops

pp. 367-68

Erythronium umbilicatum

Dimpled trout lily

pp. 370-71

Impatiens pallida

Yellow jewelweed

pp. 391-92

Monarda didyma

Crimson bee balm

pp. 406-7

Phacelia fimbriata

Fringed phacelia

pp. 419-20

Rudbeckia laciniata

Cutleaf coneflower

pp. 433-34

Solidago curtisii

Curtis's goldenrod

p. 443

Stellaria púbera Trillium erectum Uvularia grandiflora

Invasive Exotic Plants

Giant chickweed p. 447

Wake robin, Stinking Willie p. 457 Large-flowered bellwort p. 462

Celastrus orbiculatus Rare Plants

Oriental bittersweet p. 277

'Aconitum reclinatum tCorallorhiza maculata

White monkshood Spotted coralroot

= plant not included in the species profiles (Part IV)

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