map | (in two parts, 1-NW and 1-SW) of Western United 
States has names of counties, also adjacent Provinces of 
Canada and States of northern Mexico. Base map 2—N of North 
America contains names of States of the United States, 
Provinces and other subdivisions of Canada, States of Mexico, 
and names of additional countries. 
The base map of the United States is the same, scale 
1:10,000,000, Albers Conical Equal Area Projection—standard 
parallels 294/2.° and 451/2°. Lines show State and county 
boundaries, also borders of adjacent Provinces of Canada and 
States of Mexico, and crosses at 5—degree intervals mark 
latitude and longitude. However, because of the reduced page 
size, this base has been trimmed into four smaller ones, two 
horizontal and two vertical. Two additional horizontal bases 
were drafted with extended borders, one northward through 
Vancouver Island, Canada, and the other southward to the end 
of Baja California, Mexico. On all these maps 1 inch equals 
approximately 158 miles and 1 centimeter, 100 kilometers. 
The second base map, North America, is added for species 
whose natural range extends beyond the limits of the first. 
Thus, the entire distribution is included, with rare exceptions, 
such as species spreading into other continents. This one-page 
base map of North America represents a reduction to about 
one-third the scale of the United States base, roughly 
1:32,000,000. Thus, 1 inch equals about 500 miles, and 1 
centimeter about 320 kilometers. State and national boundaries, 
also principal rivers, and latitude and longitude are shown. 
Base map 3, National Forest System and Related Data, shows 
the location of the 155 National Forests, which are widely 
distributed in 40 States, also the 19 National Grasslands in 12 
States. Comparison with a tree species map will indicate the 
National Forests where that species may be expected. Many 
tree species occur also within specially managed smaller areas, 
such as experimental forests and research natural areas. 
List of Maps (pages iii—vi) cites the number and order of maps 
of the 210 species. The order is alphabetical by scientific name. 
Thus, a map can be found quickly. Also, related species in the 
same genus are placed together. Index of Common Names and 
Index of Scientific Names follow the maps. 
Each of the 210 species has a separate map, 70 also a 
second, and 6 of these also a third. Thus, the total is 286 maps, 
also 4 pages of base maps. The map of North America is added 
for 21 species whose natural range extends beyond the limits of 
the United States map northward into Canada or also Alaska 
and for 41, southward into Mexico or beyond. 
Where there is more than one for a species, the number is 
followed by letters for the base map: W (Western United States, 
vertical), NW (Northwestern United States, horizontal), SW 
(Southwestern United States, horizontal), and N (North Amer- 
ica). Fifteen species project vertically from north to south onto 
two horizontal maps. If a species has two, the maps are on 
facing pages. If three, that of North America precedes or 
follows the others. To avoid separating maps of a species, minor 
exceptions to alphabetical order were necessary, as noted under 
List of Maps. 
The legend at the base of many maps contains additional 
notes. For species of local or limited distribution the names of 
States are mentioned. Also, occurrence beyond the map is 
indicated. The range of each species is summarized in the 
Forest Service Check List (Little 1953). 
The natural distribution or range of a tree species, as mapped 
in this Atlas, is the geographical area where the species, 
including any and all varieties, is native or wild. Varieties have 
not been plotted separately, and hybrids are omitted. 
The distribution of the native tree species of the United 
States is mapped as of the present time, exclusive of changes 
caused directly or indirectly following settlement by Europeans. 
However, where modifications have occurred, the distribution is 
intended to be before Columbus, or pre-Columbian. For nearly 
all native tree species, the man-caused changes in range limits 
up to the present are believed to be negligible or recognizable. 
Most of the western half of the country has been settled less 
than a century. The commercial timber supply in the West is 
still partly from virgin forests. Vast areas of natural forests 
remain in the Western States, mostly in less accessible parts of 
the National Forests. In the East, including agricultural and 
urban areas, sufficient scattered trees and secondary forests 
remain to show the natural distribution. However, total destruc- 
tion has taken place in cities and artificial lakes. 
These maps do not show where a species grows outside the 
natural range after having been introduced directly or indirectly 
by man, whether planted, escaped, adventive, or naturalized. 
Records of planted or introduced trees outside the continuous 
natural ranges have not knowingly been mapped. Reports of 
trees planted for forestry, shade, or other purposes and of 
escapes from cultivation have been omitted. Also excluded are 
naturalized trees, those introduced outside their natural range 
and thoroughly established and reproducing as though native. 
Perhaps in the future, maps adding forest plantations or other 
successful introductions beyond the original occurrence may 
merit compilation. In the meantime, maps of Plant Hardiness 
Zones, such as overlay 4 of Volume 1 (Little 1971; U.S. National 
Arboretum 1965), may suggest roughly where a species would 
be hardy when planted outside its natural range. 
The natural geographic distribution of each species is shown 
as a brown shaded pattern of fine dots on the black-and-white 
base map. Outlying stations or outliers are plotted similarly by 
large or small dots according to size. However, the smallest 
areas, such as a grove with only a few trees, must be enlarged 
to a dot, representing several miles in diameter, to be visible on 
a map. Width of strips, such as along rivers, has been 
broadened slightly. A few localities beyond the main range, 
where a species is known to have occurred naturally within 
historic times but is now extinct, are designated by x. Arrows 
have been added to direct attention to isolated dots. 
Presence or absence is shown, but not abundance or density. 
Large areas within the main range where a species is known to 
be absent, for example, high mountains, are marked by borders 
or holes unshaded within. Commercial range, formerly indicated 
on some old maps, is not designated. Altitudinal limits, which 
vary in different latitudes, are not indicated. 
The North American map of a species repeats on smaller 
scale the distribution pattern from the United States base. 
Additional dots beyond the main range in Canada and Mexico 
mostly are fewer and scattered and are enlarged for clarity. 
The species maps do not indicate forest types, or forest cover 
types, which are the subject of overlay 9, Major Forest Types, 
in Volume 1. Most tree species are not confined to a single 
forest type and have ranges somewhat beyond. However, many 
species are characteristic of and largely within certain broad 
types. Published colored maps of vegetation and forest types 
have been mentioned. Colored maps of forest types are 
contained in forest survey publications by the Forest Service for 
States. The comprehensive classification of forest cover types 
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