This is a field guide to the identification of over 500 of some 679 species of trees native to North America north of Mexico. Included are the most common and most important species and also many that are less familiar but no less interesting. In addition, important foreign species that have become naturalized and some that are grown commercially or as ornamentals are also described and illustrated. In total, the guide includes nearly 600 species in 76 families.
The criteria used to determine which species to describe and illustrate and which to only mention are based on the definition of a tree. Native woody plants that regularly attain a height of 20 feet have been included, as have major introduced and naturalized species. A more difficult group were those woody plants that are treelike in only part of their range, in optimum habitats, or under special conditions. The more widespread, abundant, and important the plant, the better its chances for inclusion. Many of these smaller trees (to 15 feet) and some species that have limited ranges are mentioned, however.
Willows and hawthorns include many local species difficult to identify. Those that are of unquestionable tree size or that are the only representative in an area have been included.
To make this book most useful in the field, the text, range maps, and illustrations have been brought together so that all pertinent information can be seen at a glance. Because of limited space, the text is necessarily brief and therefore not complete in every detail, but the combination of text, range map, and illustrations will aid greatly in making identifications in the field.
Some trees have such distinctive forms that they can be identified at a glance, even at a considerable distance or from a moving car. A number of trees may be recognized quickly by their bark or by some unique character of the twigs, such as thorns or spines. Others may require a careful study of their flowers, fruits, buds, or detailed features of the foliage to confirm an identification. The range maps indicate the probability of finding a species in a particular area and, except for ornamentals planted outside their natural environment, are important, too, in tree identification. Range maps are especially helpful in identifying trees in such groups as the willows and hawthorns. These maps give only a general picture of where the species may be found, for within its range each species typically grows in a particular habitat, as in swamps, along rivers, or on alpine slopes. Some species are so tolerant of soil, moisture, and sunlight requirements that they are very widely distributed.
Each person develops his own method of tree identification. Often this is a combination of some characteristics that can be observed at a distance and others that need closer study. In most places, except in parks, a specimen of a leafy twig can be taken for study later at home or to show to a local authority on trees. A Bibliography is included to aid your further study.
Practice is the best way to learn to recognize trees. By observing the varied characteristics of different species and by reading further about them, distinctive features and descriptive botanical terms become commonplace. An awareness of the variations that might be expected of a species also develops with observation, for though leaves and other features of each species have a typical basic form, size, color, or other characteristic, often there is considerable variation in individuals of the same species. With field experience, the pleasure and satisfaction gained from this fascinating hobby is greatly increased. As a suggestion, underline in this book those field marks that are most helpful to you, especially those useful in differentiating a species from a similar species.
Technical terms have been held to a minimum in this field guide. In fact, an effort has been made to simplify terms wherever possible in the brief descriptions and to emphasize only the most obvious field characteristics that may not be obvious in the illustration. Comparing a specimen with the illustrations and the description reduces the need for these technical terms. Some of the most commonly used terms for parts of trees are given on here, however. If a tree cannot be identified by quick reference to this guide, the use of such terminology will be of great help in conferring with tree experts or in using more technical references.
As a further aid to finding information quickly, this guide has a complete index to common and scientific names. And the illustrated guide to family characteristics here will help in fitting a tree to its group and also in comparing features of the various families.
Common and scientific names in this book are based largely on the Checklist of United States Trees (Native and Naturalized) by Elbert L. Little, Jr., prepared under the direction of the Forest Service Tree and Range Plant Name Committee (see Bibliography). Nomenclature, initially taken from the 1953 edition of that publication, has been updated to conform largely to that in the 1979 edition. Recognized botanical publications were also consulted in certain instances to determine the names for ornamental or naturalized species included in this guide but not in the Checklist.
Many trees, as well as other plants, have several common names, varying with different localities. For this reason, botanists use scientific names that are written in Latin, a language that is no longer spoken and hence does not change with time. Each name consists of two parts—the genus and the species. Thus the scientific name of Sugar Maple is Acer saccharum; of Eastern Redcedar, Juniperus virginiana; of White Oak, Quercus alba. Regardless of nationality or native language, botanists anywhere in the world can recognize trees, as well as other plants and animals, by this naming system. Tree species also have varietal forms. A few examples of these are included in this book, as in Lodgepole Pine, Pinus contorta var. latifolia.