LISTS AND OTHER AIDS

To Know the Trees

IMPORTANT FOREST TREES OF THE UNITED STATES

ELBERT L. LITTLE, JR.

FOR A SELECTED LIST of 165 important native forest tree species of the United States the following information is compiled here: (1) Approved common and scientific names, as well as other names of lumber and other names in use; (2) drawings, keys, and nontechnical descriptive notes for identification; (3) distribution maps showing ranges; and (4) lists of principal uses, chiefly of the wood. This summary is intended as an introduction to the forest trees, as well as a compilation of their distribution and commercial uses.

Trees are considered here as woody plants having one well-defined stem or trunk at least 2 inches in diameter at breast height, a more or less definitely formed crown of foliage, and a height of at least 10 feet. Though the division between trees and shrubs is not sharp, shrubs typically are the smaller woody plants, usually with several branches from the ground instead of one trunk.

The kinds, or species, of native trees in the United States number about 845, excluding hybrids and varieties but including smaller trees not of commercial timber size and those classed also as large shrubs. These are further grouped into about 222 genera and 69 plant families. Of the total, about 150 species belong to the single, highly variable group, or genus, of hawthorns (Crataegus), in which numerous other minor forms (including many shrubs) have been proposed as separate species. About 110 other native tree species are tropical or subtropical trees known in the United States only from Florida. Thus, without the hawthorns and the trees confined to Florida, there are about 585 tree species native in the United States. In addition, 90 or more foreign tree species widely planted have escaped from cultivation, and have become naturalized, so that they may be considered properly as at home here. More than a third of these exotics are tropical trees limited to Florida. Many other tree species from foreign lands have been introduced as ornamental, shade, and fruit trees.

Botanists have named and distinguished also numerous varieties and more than 85 natural hybrids and apparent hybrids among the native trees, including more than 60 hybrid oaks (Quercus). However, foresters distinguish only a few botanical varieties, or minor variations, by name, although they do recognize unnamed geographic races. Aside from the hawthorns, the largest groups, or genera, of native trees are the oaks, with 57 species; willows (Salix), with 33 species; and pines (Pinus), with 34 species.

Nearly three-tenths of the 585 native tree species (excluding hawthorns and the tropical trees of Florida), or 165 species, have been selected and included here primarily for the commercial importance of their woods or other products, although a few are more important for other values in forestry. These are grouped in 51 genera, the largest groups being the oaks (Quercus), with 28 species, and the pines (Pinus), with 20 species. The species in the series of leaflets on economically important species, American Woods, by H. S. Betts, are represented, as are most of the 182 tree species designated as important forest trees in the check list by George B. Sudworth (Check List of the Forest Trees of the United States, U. S. D. A. Miscellaneous Circular 92, 1927; now out of print).

The important native tree species of Alaska and Canada are also here included, because the ranges of some species of the northern United States extend northward. These northern species are indicated by mention of Alaska or Canada (or a Canadian Province) in the notes on distribution. The 18 species of Alaska included here are more than half of the 32 native tree species of Alaska. The 89 Canadian species in this list are almost three-fifths of the 150 native tree species of Canada, excluding hawthorns (Crataegus), although some of these range northward only to extreme southern Ontario.

The 165 important forest tree species of the United States have been separated into two lists, eastern and western, because the tree species of the two regions are almost entirely different. The first list contains 110 species found in the eastern half of the United States (extending west to the prairie-plains), and the second list has 55 species found in the western half of the United States (from the prairie-plains westward including Alaska). The eastern list is larger than the western because there are more commercially important hardwood species in the East. Several species that have wide distribution in both East and West have been placed in one list, with a cross-reference in the other.

In the descriptive summary, the approved common and scientific names are those officially accepted and widely used. Other lumber names and common names in use in some localities and a few scientific names have been added as synonyms. A few important varieties are listed under the names.

Size is indicated as large (more than 70 feet tall), medium-sized (from 30 to 70 feet tall) , or small ( less than 30 feet tall) .

The descriptive notes are a summary of the leading characteristics, such as bark, leaves, and fruits and flowers, if showy or distinctive. These notes, together with the drawings (by Miss Leta Hughey) of the leaves and fruits, may be used to find tree names.

The distribution maps prepared especially for this article are based largely upon data published in various State tree manuals and State floras. Thus, the geographic areas in the United States and southern Canada as well (but excluding Mexico), where each species grows wild, or is native, are summarized concisely. However, maps are subject to certain limitations and minor inaccuracies based upon incomplete knowledge of exact distribution and limits, insufficient botanical exploration in some regions, lack of compilation of numerous herbarium and published records of range extensions, and difficulties in mapping scattered and isolated stations. In order that these maps can be revised and made more accurate, additional information on distribution, including both corrections and range extensions, will be welcomed by the author.

By showing the native ranges, these maps will aid in identification of trees. Thus, when a tree specimen is compared with drawings and descriptions, the maps indicate which species are native in a particular region and which are not to be expected there. However, many species have been planted beyond their native ranges and often have spread by escaping from cultivation. A few, such as Osage-orange, black locust, and northern catalpa, have become widely naturalized.

The notes on principal uses have been compiled largely from data in the leaflets, American Woods, by H. S. Betts, published by the Department of Agriculture in 1945.

To assist in the identification of trees, a simplified key, based chiefly upon leaves and twigs, has been inserted in the text. This key is an outline in which trees with certain characteristics in common are grouped together. The name of a tree specimen is found by elimination through successive selection of one from a pair of groups, with descriptive characters that fit the specimen. The paired groups are designated by the same letter, single and double, beginning with "A" and "AA," at the left of the page. Under the group fitting the specimen, the elimination continues with the next paired groups indented below, such as from "AA" to "N" or "NN" and from "NN" to "O" or "OO," the pair next indented to the right, until the name is reached. Some descriptive notes applying to a genus have been inserted in the key and not repeated in the notes under each species. The key is limited to the tree species represented here and will not serve to identify other trees. Identifications, of course, may be made directly from the drawings, maps, and descriptive notes, without use of the key.

The arrangement of species in the lists of eastern and western trees is artificial, to fit the key, rather than botanical. In each list the conifers are placed first, sorted into those with needlelike leaves and those with scale-like leaves, followed by broadleaf trees. The latter are grouped into trees with paired (opposite) simple leaves, trees with paired (opposite) compound leaves, trees with single (alternate) compound leaves, and trees with single (alternate) simple leaves, with the oaks placed last. (A compound leaf is divided into leaflets, which usually are smaller than leaves and are attached on a common leafstalk that sheds with them. Also, the leaf has a developing bud at its base, while the leaflets of a compound leaf do not.)

Various handbooks, manuals, and other publications may be consulted for the identification of the trees of the United States, especially those not found here, and for additional information. A list of 30 references for identification of trees, both popular and technical, including the illustrated books on the commoner trees of the United States and books on the trees of geographic regions, will be found in the bibliography. Trees are described also in the various botanical floras and manuals, usually technical and without illustrations, which have been pre- pared for geographical regions, single States, or smaller areas.

The State forester can furnish information about publications on the trees of your State and how to obtain them.

To identify with certainty the numerous kinds of native trees, some of which differ but slightly, some knowledge of systematic botany or dendrology as well as of the technical terminology is desirable. Properly prepared dried and pressed botanical specimens of twigs with leaves and flowers or fruits may be submitted for identification to specialists, such as to departments of botany and schools of forestry in universities and colleges, to botanical gardens, herbaria, and museums, or to the United States Department of Agriculture. Specimens should be accompanied by notes, such as locality where found, collector's name, date, size, whether wild or planted, and other data of interest. Material for the Department of Agriculture may be sent to either of the following: Forest Service, Washington 25, D. C.; or Bureau of Plant Industry, Soils, and Agricultural Engineering, Plant Industry Station, Beltsville, Md.