8i6 



Yearbook^ of Agriculture 1949 



For a tropical atmosphere, hardy 

 trees that are representative of their 

 relatives from warmer lands can be 

 grown northward. Examples are silk- 

 tree ( "mimosa" ) , with its f ernlike foli- 

 age and pink, ball-like blossoms; ail- 

 anthus, with its coarse, compound 

 leaves; and royal paulownia, with its 

 big leaves and striking clusters of large 

 violet flowers. Certain nut trees and 

 fruit trees can serve a double purpose 

 for shade or ornament also. 



For forestry purposes, such as in 

 reforestation of large areas through es- 

 tablishment of plantations, native trees 

 generally have been more satisfactory 

 than introduced trees. Scotch pine and 

 Norway spruce, the most popular for- 

 eign forest trees, have been planted 

 chiefly in the Northeastern States. 

 California has its plantations of euca- 

 lyptus from Australia. In the prairie- 

 plains shelterbelts, several exotic trees, 

 such as the following, have been suc- 

 cessful: Siberian elm, Chinese elm, 

 Russian-olive, Russian mulberry, Aus- 

 trian pine, white willow, and ailanthus. 



In this article 50 species of the com- 

 monest and most popular trees from 

 foreign lands are described briefly and 

 illustrated, primarily for their identifi- 

 cation. Though emphasis has been 

 given to the trees widely planted for 

 shade and ornament in temperate re- 

 gions of the United States, about a 

 fourth of the species selected are tropi- 

 cal trees restricted to the subtropical 

 regions along the southern border from 

 Florida to California. 



Several are no longer widely recom- 

 mended, because of objectionable fea- 

 tures or susceptibility to disease or in- 

 sects or because some better kinds are 

 available, though they may be suitable 

 for special purposes. Nevertheless, 

 they have been planted so frequently 

 that they merit inclusion in a list used 

 for identification purposes. Nearly half 

 of these 50 species have already be- 

 come naturalized and grow in their 

 adopted home as if native. 



The description of each tree species 

 contains the approved common and 

 scientific names as well as other names 



frequently used. Size is stated as large 

 (more than 70 feet tall), or medium- 

 sized (30 to 70 feet tall) , or small (less 

 than 30 feet tall) . Leading character- 

 istics useful in identification, such as 

 form of the tree, bark, leaves, flowers, 

 and fruits, are briefly described in non- 

 technical terms. However, some horti- 

 cultural varieties with unusual or ex- 

 treme characteristics may differ from 

 the general descriptions. Though many 

 trees reveal their geographic origin in 

 their names, the native home is stated 

 along with the regions in the United 

 States where the species is grown. 



Notes on special uses and desirable 

 qualities as well as objectionable 

 points are included. The drawings of 

 leaves and fruits by Leta Hughey, bo- 

 tanical artist, Forest Service, will aid in 

 naming trees or specimens. 



The degree of hardiness of intro- 

 duced trees and shrubs to cold weather 

 in winter is expressed by division of 

 the United States into hardiness zones, 

 climatic zones based upon average an- 

 nual minimum temperatures (U. S. 

 D. A., Atlas of American Agriculture, 

 Climate, page 9, figure 1928). Alfred 

 Rehder (Manual of Cultivated Trees 

 and Shrubs, edition 1, 1927; edition 

 2, 1940), Donald Wyman (Hedges, 

 Screens, and Windbreaks, 1938), and 

 other authors on horticultural subjects 

 have adopted these hardiness zones, 

 citing the northernmost zone where 

 each species can be grown. 



On the next page is a revised map of 

 hardiness zones of the United States, 

 based upon the map of average annual 

 minimum temperature for the 40-year 

 period from 1899 to 1938 (U. S. D. A., 

 Climate and Man, Yearbook of Agri- 

 culture, page 707. 1941). 



Ten zones for North America have 

 been designated by number, beginning 

 with zone 1, with average annual mini- 

 mum temperature exceeding 50 F. 

 and representing the treeless zone of 

 northern Canada and Alaska. The 

 nine zones of the United States with 

 their limits of average annual mini- 

 mum temperature (Fahrenheit) are, 

 from north to south: Zone 2, 50 to 



