INTRODUCTION

INTRODUCTION:

The name Pennsylvania, "Penn’s Woods", indicates a land lush with a wide variety of trees. In Pennsylvania the geographic ranges of many species typical of the northern temperate zone intersect with those of the south, producing a unique diversity of trees. Nearly all species of trees native to temperate eastern North America grow in the state. By studying the trees of Pennsylvania, you will be introduced to some of the most prominent flora of the region.

Trees are the largest and some of the most impressive plants in the world. Their size, age, and beauty inspire wonder and excitement in us all. The importance of trees to man and the rest of the biota as sources of food, shelter, shade, fuel, wood products, oxygen, and erosion control, expand our appreciation of trees. To learn their identity and natural history adds to the understanding of these giants of the plant kingdom. In addition, learning to identify trees will not only add to your appreciation of the American countryside, but it also will serve as an introduction to concepts in biodiversity, taxonomy, and plant anatomy and physiology. Furthermore, a knowledge of the names of trees, their botanical features and their natural history are fundamental to all studies in forestry, environmental science, and botany.

Dendrology is the study of botanical trees. However, the definition of botanical trees is not clear-cut; the line between trees and shrubs is not absolute. A forester may define a tree based on the presence of a substantial trunk, as a source of merchandisable timber. An ecologist is likely to define a tree in terms of the plant’s competitive ability, as a unit of casting shade on other plants, and as a producer of photosynthetic compounds. A physiologist would be concerned with the rigidity of the plant, as a plant able to produce lignin and vascular cambium. For the sake of convenience, a tree typically is defined as a woody plant that reaches 13 to 20 feet or more in height at maturity, with a single trunk, unbranched for several feet above the above the ground, and having more or less a definite crown (Harlow et al., 1991).

Taxonomy is concerned with nomenclature, the assignment of names to organisms. Historically there have been two nomenclatural systems in botany: scientific names and common names. The forester and environmental scientist learn both in order to communicate effectively with both their colleagues and the general public. Common names have been assigned by people based on characteristics like habitat (Mountain Hemlock), distinctive features (Black Cherry), or use to man (Sugar Maple). These names are used in everyday speech and writing, but they are not precise enough to be used in scientific communication. Science uses a standardized, universal nomenclature using latinized names. Scientific names have followed standard usage since 1753 when Linnaeus published his monumental book entitled Species Plantarum. Since that time it has been convention to write the genus (capitalized) followed by the species (lower case). In scientific writing, both names are either underlined or italicized. The genus may be abbreviated with its initial only if the content is clear, and the genus name has been spelled out previously. For example, Tsuga canadensis, Prunus serotina, and A. saccharum are all correct usages of scientific names for the common-named trees, Mountain Hemlock, Black Cherry, and Sugar Maple.

In taxonomic classifications, the species is the focal point. It is the basic group of potentially interbreeding populations of individuals that share common characteristics, and are morphologically and often ecologically distinct from related species. A species is a concept that is variously defined, so taxonomists may disagree about the level of recognition of a group; a species to one taxonomist may be a "variety" or "subspecies" to another. Such flexibility in the concept is necessary to reflect the complexity of nature. Above the species level are categories of classification that serve to show other relationships. A genus groups together similar species, distinguishing the group from the other genera. Similarly, a family is composed of genera; and an order is composed of families. The top level in plant classification is the phylum. Table 1 shows twelve families of trees native to northeastern United States. These families are not exclusive to this region, nor are they the only families you will find in a Pennsylvania woodland. They are, however, among the most common and well-known tree families of the region.