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Trees of Pennsylvania

Authoritative, encyclopedic, lavishly illustrated guide to the trees of the state and region—from the Morris Arboretum, the official arboretum of the Commonwealth of Pennsylvania.

Trees of Pennsylvania
A Complete Reference Guide

Ann Fowler Rhoads and Timothy A. Block. Illustrations by Anna Anisko

2004 | 416 pages | Cloth $59.95
Botany / Ecology/Environmental Studies
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Table of Contents


Chapter 1. What is a Tree?
—Growth patterns
—Short shoots and long shoots
—Fall leaf color
—Root partners
Flowers, fruits, and seeds
—-Seed dispersal
Clonal growth

Chapter 2. Pennsylvania's Forest Heritage
A brief history of Penn's Woods
Cutting down the trees
—Early lumbering
—The "Great Clearcut"
The forest today
Too many deer
Impact of pests and diseases
Native versus introduced species
Rare species
Forest succession
Major forest types
The value of trees

Chapter 3. Descriptions, Illustrations, and Distribution Maps

Alder — Apple — Aralia — Arbor-vitae — Ash — Atlantic white-cedar — Basswood — Beebee tree — Beech — Birch — Blackgum — Blackhaw — Bladdernut — Buckeye — Catalpa — Cherry — Chestnut — Chinese toon-tree — Corktree — Crabapple — Dogwood — Douglas-fir — Elm — Empress-tree — Fir — Fringetree — Ginkgo — Golden rain-tree — Hackberry — Hawthorn — Hemlock — Hickory — Holly — Honey-locust — Hoptree — Hop-hornbeam — Hornbeam — Juniper — Katsura-tree — Kentucky coffee-tree — Larch — Locust — Magnolia — Maple — Mimosa — Mountain-ash — Mulberry — Oak — Osage-orange — Pagoda-tree — Paper-mulberry — Pawpaw — Pear — Persimmon — Photinia — Pine — Plum — Poplar — Prickly-ash — Redbud — Sapphire-berry — Sassafras — Shadbush — Silverbell — Snowbell — Sourwood — Spruce — Sumac — Sweetgum — Sycamore — Tree-of-heaven — Tuliptree — Walnut — Willow — Witch-hazell

Chapter 4. How to identify trees
Identification Keys

Tree Lists
Native Trees that are Important Food Sources for Moths and Butterflies
Small to Moderate-size Native Trees with Conspicuous Flowers
Native Trees with Edible Fruits
Endangered, Threatened, and Rare Trees of Pennsylvania
Native Early Successional Trees (sun-loving)
Native Trees of Riparian Forests
Native Wetland Trees
Trees that are at or Near the Southern Limit of their Natural Range in Pennsylvania
Trees that are at or Near the Northern Limit of their Natural Range in Pennsylvania
Trees that are at or Near the Eastern Limit of their Natural Range in Pennsylvania
Pennsylvania Trees Listed by Family


Excerpt [uncorrected, not for citation]

Chapter 2. Pennsylvania's Forest Heritage

A Brief History of Penn's Woods
The land that greeted the earliest Europeans to arrive in Pennsylvania was primarily forested, broken only by rivers, occasional wetlands, and clearings associated with Native American villages. Early accounts of the landscape of the interior of Pennsylvania contain frequent references like this descriptive passage by Fortescue Cumming while crossing Tuscarora Mountain in 1807, "view to the westward, though extensive, was cheerless and gloomy, over a broken and mountainous or rather hilly country, covered with forests, chiefly of the dark and sombre pine . . .". Other accounts describe extensive grasslands and gallery-type forests in which one could "drive a carriage unhindered," apparently the product of Native Americans' regular use of fire to manage the landscape.

However, that forest is a fairly recent product of the geological evolution of Pennsylvania's landscape. Eighteen thousand years ago the northeastern and northwestern corners of the state were covered with ice, and tundra and boreal forests covered the rest of the state. As the ice receded, species that had found refuge farther south gradually returned.

Influence of Native Americans
The popular notion that European explorers and early settlers found a primeval forest free of human influence is inaccurate. Fossil pollen and charcoal preserved in bogs and lake sediments all across the eastern half of North America, as well as many of the earliest written observations, record wide-scale use of fire by Native Americans to manage their landscape. Evidence exists that Native Americans managed vast areas of forest with fire to create open, gallery-type forests, encourage species they prized for food, and also to clear fields where they grew corn, beans and other crops.

The oak-dominated forests that persist today, and native grasslands, most of which disappeared soon after Native Americans were ousted from the land, almost certainly owe their existence to traditions of large-scale burning among some groups of people for centuries or thousands of years before the arrival of Europeans.

Native American populations were much larger before contact with Europeans introduced smallpox and other diseases; the extent of land impacted by their management was large. The first European settlers found extensive clearings created by Native Americans in the Cumberland Valley, Penns Valley in Centre County, and the Wyoming Valley, as well as other sites. Revealingly, later travelers in these same regions described a forested landscape apparently due to successional growth.

Cutting Down the Trees
As European settlers claimed the land, taming the wilderness meant cutting down trees and eradicating some forest wildlife, especially large predators, in order to make room for farms, towns, and villages and to assure the safety of pioneer families and their livestock. Wood not needed for fuel or building material was often burned early in the process of clearing the land; after all, there was a seemingly unlimited supply.

In Pennsylvania, the clearing for farming and cutting trees for commercial uses that began with the first European arrivals had, by 1900, reduced the forest cover from 90-95 percent of the land area to 32 percent.

Early lumbering—Tall, straight, and suitable for masts for ships, the eastern white pine was the first large-scale target of waves of loggers who assaulted Pennsylvania's forests. Beginning in the 1760s, white pine logs 120 feet long and 4 feet in diameter (or larger) were cut in the hills of northeastern Pennsylvania, fastened together in huge rafts, and floated down the Delaware River to Philadelphia to provide masts for British ships.

A second wave of timber harvesting focused on hemlock bark, which was used in the leather tanning industry. Hemlock logs were cut and the bark stripped off and hauled to tanneries located in many parts of the state near the source of bark.

Charcoal making was another forest industry that thrived before the discovery of coal as a fuel. In areas near early iron furnaces, colliers cut trees (preferably oak or chestnut) and stacked them in conical piles built in the woods. The piles of logs were covered with earth and burned to produce charcoal that was then hauled by wagon to the iron works. Charcoal making utilized small trees and could be done on a 25-year rotation in most areas. An iron furnace required 20,000-35,000 acres of forest to support it on a sustainable basis. Today, it is not unusual to come across old charcoal hearths, level areas about 40 feet in diameter, scattered throughout the forests in areas where charcoal making occurred.

The "Great Clearcut"—The invention of the geared logging locomotive set the stage for the great clearcut of Pennsylvania's forests that took place between 1890 and 1930. The railroad logging era, as it is known, allowed loggers to reach the vast interior of the state's forests. Rail beds were constructed up every hollow, far into forests unreachable when proximity to water was necessary to transport the logs to markets. Today many of the old railroad beds are the basis for a network of hiking trails.

During the railroad logging era, technology was present not only to harvest vast areas but also to utilize everything regardless of species or size. What wasn't usable as lumber was treated by slow heating and distillation in "chemical factories" that produced acetate of lime, wood alcohol, wood tar, charcoal, and gases. Wood products including barrel staves, lath, shingles, boxes, and kindling wood were produced in hastily built factories located in temporary towns that sprang up throughout the northern tier of Pennsylvania. Old photographs record the boom days at Masten, Golinza, Laquin, and many other sites that today are only names on a map, a few old foundations, or perhaps the site of a hunting camp.

Clearcutting was frequently followed by fires; started by sparks from the railroads, the fires burned rapidly and fiercely through the slash left after logging. The resulting scenes of devastation generated concern by groups throughout the state and led to the formation of the Pennsylvania Forestry Association. A campaign led by Dr. Joseph Rothrock, resulted in the formation of a Division of Forestry within the Pennsylvania Department of Agriculture in 1895 and the appointment of Dr. Rothrock as the first Forestry Commissioner.

Development of a system of forest reserves, now known as state forests, began in 1897 with the acquisition of abandoned cut-over lands that were sold at tax sales. By 1904 the system held about half a million acres; today the state forests total 2.1 million acres.

The Forest Today
Despite dire predictions of Rothrock and others, Pennsylvania's forests did recover in the years following the great clearcut. Trees came back not only on cutover lands, but also on abandoned farmland; today, second growth forests cover 59 percent of the state's land area. Only a few fragments remain of the original forest. The Tionesta Scenic and Natural Area in Allegheny National Forest in northwestern Pennsylvania includes the only sizable tract of old growth forest that remains in the state. Heart's Content, also in the Allegheny National Forest, has 100 acres of old growth hemlock-white pine forest. Fourteen other smaller fragments are preserved in state forests or state parks.

In addition to 2.1 million acres of state forests, Pennsylvania's publicly owned forest lands include another 277,000 acres in 116 state parks. State game lands, administered by the Pennsylvania Game Commission, contain another 1.4 million acres in the public domain. Pennsylvania is host to one national forest; the Allegheny National Forest contains just over half a million acres. By far, however, the largest proportion (70 percent) of forested land in the state is privately owned.

The timber industry remains an important part of Pennsylvania's economy, totaling nearly $5 billion per year and providing about 100,000 jobs. The most valuable single product is black cherry, which is used mainly for veneer in the furniture industry. Oak and other hardwoods are also important.

Rare Species
The abundance of individual tree species varies greatly from those that are found throughout the state in a variety of habitats such as red maple, beech, and red oak, to those that are very limited in their occurrence.

Rarity occurs for several reasons; some native Pennsylvania trees such as balsam fir, tamarack, and black spruce are northern species that are at their southern limit of range in Pennsylvania. Others, such as American holly, sweetbay magnolia, southern red oak, willow oak, chinquapin, and short-needle pine, just reach the state from the south. Trees with a more western distribution that reach Pennsylvania include Shumard oak, bur oak, shingle oak, and Kentucky coffee-tree.

Others, such as chestnut and butternut, have become rare through the impact of insects or diseases. Two trees that once grew here, Atlantic white cedar and swamp cottonwood, are extirpated (gone from the state).

The rarest native species are designated by the Pennsylvania Natural Diversity Inventory (PNDI) and protected under the Wild Plant Conservation Act. Trees listed as endangered in Pennsylvania are balsam poplar, beach plum, southern red oak, willow oak, Shumard oak, and showy mountain ash. Allegheny plum and pumpkin ash have been recommended for endangered status. Classified as threatened are American holly, umbrella magnolia, sweetbay magnolia, and common hop-tree. Four other tree species, short-leaf pine and three hawthorns, have been recommended for listing but a specific status has not yet been determined.

Forest Succession
With few exceptions, rainfall, temperature, and soil conditions are suitable for the growth of trees throughout Pennsylvania. Forests and the trees and other species that comprise them are constantly changing systems. Abandoned farmland, and cleared or timbered land will become forested again through a natural process known as secondary succession. Initially open land will be colonized by species such as eastern red cedar, tuliptree, aspens, or red maple that grow well in the high light conditions of open fields. As early successional species modify the environment by increasing the organic matter and shading the forest floor, more shade tolerant species invade. Beech, sugar maple, and hemlock are so-called late successional trees because of their ability to grow and reproduce in low light conditions. The term climax forest was formerly used to describe the late successional stages of forest development. However, current interpretation is to view the forest as a constantly shifting mosaic of patches created by individual tree falls and other small-scale change.

Major Forest Types
Pennsylvania's climate, rainfall, and soil fertility support forest growth throughout most of the state with the exception of areas that are too wet or too rocky. The major forest types are northern hardwood forest, oak-hickory forest, Great Lakes beech-maple forest, and mixed mesophytic forest.

The northern hardwood forest occupies the northern third of the state and extends south at high elevations along the Allegheny Front. It also occurs further south on north-facing slopes and cool, moist ravines. This forest type is characterized by a mixture of hardwoods and conifers and usually contains beech, birch, sugar maple, hemlock, and white pine in the canopy. Wild black cherry reaches its best development in this zone, especially in the northwestern part of the state. Understory trees typically include moosewood, witch-hazel, mountain holly, and shadbush.

Oak forests dominate the southern two-thirds of the state. Oak forests include red oak-mixed hardwood type on lower slopes where red and white oaks occur mixed with tuliptree, red maple, and hickories. On drier upper slopes and ridge tops throughout the central Pennsylvania, oak forests are dominated by white, black, and chestnut oak are common. These forests have a dense layer of shrubs such as mountain laurel and black huckleberry. Before 1910, American chestnut was an important component of Pennsylvania's oak forests, but the accidental introduction of chestnut blight in New York City in 1904 resulted in chestnut's shift from widespread canopy dominant to minor status within just a few decades.

The Great Lakes beech-sugar maple forest is represented at the western end of the state. The mixed mesophytic forests, which reach their greatest development in the Smoky Mountains, just reach southern Pennsylvania. These forests contain tuliptree, sugar maple, beech, basswood, red oak, cucumber-tree, yellow buckeye, Ohio buckeye, white ash, and black cherry. Understory trees include flowering dogwood, pawpaw, umbrella magnolia, redbud, and witch-hazel. The herbaceous layer is very rich and diverse.

In the southeastern corner of the state, in a narrow sliver of the Atlantic Coastal Plain physiographic province that parallels the Delaware River, coastal plain forests contain sweetgum, willow oak, southern red oak, and sweetbay magnolia. In the northeastern and northwestern corners of the state, in areas covered by ice during the most recent glaciation, peat deposits support forests with a northern character dominated by black spruce and tamarack.

Serpentinite rock, which occurs in a band of outcrops stretching across southern Delaware, Chester, and Lancaster counties, supports forests of pitch pine or Virginia pine, coupled with red cedar, scrub oak, blackjack oak and sassafras. Shale barrens and limestone barrens of the Ridge and Valley physiographic province contain drought-tolerant species including red cedar, Virginia pine, table mountain pine, yellow oak, post oak, hackberry, and sumac.

Riparian areas throughout the state, where periodic flooding is a limiting factor, are characterized by sycamore, silver maple, box-elder, American elm, red elm, black willow, green ash, black ash, black walnut, and red maple. River birch occurs along rivers and streams in the eastern part of the state but not in the west. Swamp forests along Lake Erie are the only locations where pumpkin ash occurs.

Sixty-two distinct tree-dominated natural community types have been described for Pennsylvania.

Altered Forests
Impact of pests and diseases—Pennsylvania's forests have also been profoundly affected by pests and diseases introduced from different parts of the world. The chestnut blight fungus, first discovered in New York City in 1904, swept through Pennsylvania reducing what had previously been our most abundant tree to minor status. The gypsy moth, which spread into the state following its accidental release in eastern Massachusetts in 1869, reduced the importance of oaks through preferential feeding on members of the genus Quercus. Beech bark disease, which appeared in Nova Scotia about 1920, is still spreading across the northern half of the state reducing beech to groves of young sapling-size root shoots. Dutch elm disease and dogwood anthracnose have taken their toll. The most recent invader, hemlock woolly adelgid, is killing our state tree the Canadian hemlock in southern and eastern parts of the state. Mild winters have allowed the adelgid to spread rapidly.

Recent outbreaks of native insects such as elm spanworm, forest tent caterpillar, eastern tent caterpillar, and cherry scallop-shell moth have caused extensive tree death in some parts of the state. Research is ongoing to understand the cause(s) of a widespread dieback of sugar maple centered in Pennsylvania. Soil nutrient changes caused by acid rain appear to be part of the problem.

Too many deer—Over-abundant deer are a serious threat to the health of forests throughout the state. Deer have consumed the lower layers of vegetation including tree seedlings and saplings, shrubs, and herbaceous species. Fencing to exclude deer is now a standard practice on state forest lands when timber is harvested; this is necessary to allow new trees to become established and grow beyond the browse line (the height deer can reach). However, short-term fencing does not allow forest shrubs or wildflowers, which never outgrow the reach of deer, to escape devastation.

Native vs. introduced species—Native species are defined as those that were here before the first Europeans arrived. One hundred and thirty five species of trees are considered native to Pennsylvania. Many others have arrived subsequently through deliberate or accidental introductions from other parts of the world. The 65 nonnative trees included in this book are species that have spread into our native forests or other natural habitats. Some of them such as Norway maple, tree-of-heaven, and empress-tree have seriously impacted remnant forests in urban and suburban areas. Others including corktree, bee-bee tree, callery pear, and mimosa are just beginning to show invasive tendencies.

Some native species such as umbrella magnolia and American holly are frequently cultivated and sometimes spread into nearby woodlands from cultivated sources, making a determination of their true status more difficult.

The Value of Trees
The ecological importance of forests and trees to the well-being of the state is enormous. Trees dominate the landscape and provide habitat structure for a multitude of other plants, animals, invertebrates, and microorganisms, thereby protecting biological diversity. Like other green plants they utilize carbon dioxide and produce oxygen and sugars. They protect the soil and facilitate ground water recharge by reducing runoff and erosion. The cooling effect from transpiration and shading add to our comfort. Trees are also beautiful and restful to look at, conveying a sense of pleasure and well-being.

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