summarized in the two editions of his “Check List of Forest 
Trees of the United States, Their Names and Ranges” (Sud- 
worth 1898, 1927). “Forest Trees of the Pacific Slope” (Sud- 
worth 1908) contains much detailed information about tree 
ranges. 
Soon after establishment of the Forest Service in the United 
States Department of Agriculture in 1905, Sudworth undertook a 
project of preparing a distribution map for each native tree 
species of North America, exclusive of those occurring wholly in 
Mexico and minor tropical trees of southern Florida. Many 
thousand locality records for individual species were filed on 
separate cards from publications such as botanical lists and 
forest surveys, unpublished field notes, and herbarium speci- 
mens. For each species these localities were plotted by number 
on one or more large cloth-backed maps of contiguous United 
States, North America, or Alaska. These maps and card file are 
preserved in the dendrology project, Timber Management 
Research, USDA Forest Service, Washington. D.C. 
Publication of these maps was begun by Sudworth (1913) 
under the title, “Forest Atlas—Geographic Distribution of North 
American Trees.” Only “Part [—Pines” ever appeared. How- 
ever, four bulletins on Rocky Mountain conifers by Sudworth in 
1915-18 contain small species maps prepared for the larger 
reference. A fifth, posthumous bulletin (Sudworth 1934), has 
maps of poplars (Populus), principal tree willows (Salix), and 
walnuts (Juglans) of the Rocky Mountain region. 
It is indeed unfortunate that Sudworth’s entire Atlas, with a 
map for each of nearly 500 native tree species then distin- 
guished, was not issued promptly, when representing current 
knowledge. Some years later, Munns (1938) published distribu- 
tion maps of 170 important forest tree species of the United 
States. With minor additions, the maps were based very largely 
upon data by Sudworth, who died in 1927. 
Besides “Volume 2, Alaska Trees and Common Shrubs” and 
the California reference cited above, other publications of the 
Forest Service have been devoted to maps of the trees of a 
single State. In 1941-50, its Forest Survey published distribution 
maps of commercial forest trees in four Southeastern States, 
Mississippi, North Carolina, South Carolina, and Virginia. 
COVERAGE OF THIS VOLUME 
“Atlas of United States Trees, Volume 3, Minor Western 
Hardwoods” continues “Volume 1, Conifers and Important 
Hardwoods.” The Forest Service “Check List of Native and 
Naturalized Trees of the United States” (Little 1953) serves as a 
basis for the species included as trees, also their accepted 
scientific names and approved common names. That reference 
contains other common names in use (‘Index of Common 
Names,” p. 451-472) and current synonyms of the scientific 
names. Thus, names of species not found in this volume may be 
traced and correlated. Several minor changes in nomenclature 
made after publication of the 1953 edition are noted under 
“Tree Names” (page 6). 
The Check List apparently is the only current compilation of 
the native woody-plant species which reach tree size and which 
should be mapped in this Atlas. Obviously, the number of tree 
species included here depends somewhat upon the definition 
used. That of the Check List (Little 1953, p. 5) is followed and 
repeated here, with insertion of approximate metric equivalents: 
Trees are defined as woody plants having one erect perennial 
NO 
stem or trunk at least 3 inches’(7.5 centimeters) in diameter at 
breast height (44/2 feet or 1.4 meters), a more or less definitely 
formed crown of foliage, and a height of at least 12 feet (nearly 
4 meters). 
Large willows (genus Salix) with several trunks from the same 
root have been included. However, a few species of willow 
rarely recorded as trees have been excluded, as cited under 
“Tree Names.” 
Species whose individuals sometimes reach the above dimen- 
sions somewhere within their natural range have been included 
in this Atlas as well as the Check List. Many of the minor 
hardwoods mapped here are commonly smaller over most of 
their ranges and are regarded locally as shrubs. Several 
borderline species were mentioned in notes in the 1953 Check 
List. Most of those are described in current floras as becoming 
small trees and have been added here under “Tree Names.” 
Inclusion of these shrubby trees has increased the number of 
maps and also time of preparation. Obviously, many species of 
large shrubs are excluded. Thus, the extra maps of this volume 
may be useful in the absence of a similar Atlas on the larger 
number of native shrubs. 
Volume 3, “Minor Western Hardwoods,” with 210 species 
aims to complete the maps of the tree species native within the 
ll far western contiguous States from Washington to New 
Mexico, also Trans-Pecos Texas (the southwestern part west of 
the Pecos River; base map 2—SW). These States, mentioned 
previously, are Washington, Idaho, Montana, Oregon, Califor- 
nia, Nevada, Utah, Wyoming, Colorado, Arizona, and New 
Mexico. 
Thus, all native tree species listed within these 1] Far 
Western States are mapped within Volumes 1 and 3. Volume 1 
has about 102 western tree species, all the western conifers, or 
cone-bearing softwoods, including the needleleaf evergreens, 
totaling 68 species (also 1 shrub) and also 34 species of 
hardwoods classed as important. As Volume 3 contains maps of 
210 minor hardwoods, the total number of western tree species 
accepted in both volumes as native is approximately 312. 
Volume 3 contains all remaining tree species native in the 1] 
far western contiguous States not in Volume 1. These trees are 
classed as angiosperms, or flowering plants. The term hardwood 
generally is used for trees of dicotyledons, flowering plants with 
trunks of bark and wood usually hard, which increases in 
thickness by annual growth rings. Also added to this volume are 
12 tree species of monocotyledons, flowering plants whose 
trunks are not divided into bark and wood and whose less 
compact woody tissue does not increase in thickness by growth 
rings. These western monocotyledons, mostly of the Mexican 
border States, are included here for completeness, though 
technically not hardwoods. Nine southwestern species of Yucca, 
yucca, and Nolina bigelovii, Bigelow nolina, reach tree size. 
The only southwestern palm is Washingtonia filifera (Linden) 
H. Wendl., California Washingtonia. Another species, Sabal 
mexicana Mart., Mexican palmetto, barely reaches extreme 
southern Texas. 
Covered in part is the row of six Midwestern States of North 
Dakota, South Dakota, Nebraska, Kansas, Oklahoma, and 
Texas. Most tree species are clearly western or eastern, but 
several are widespread across the country. However, about 30 
western species extend eastward into one or more of these six 
Midwestern States but not beyond. Thus, for convenience, the 
entire range of these species is shown on a single map in this 
volume. Also included here are about 15 species of subtropical 
