764 



Yearbook of Agriculture 1949 



cus), 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 Cir- 

 cular 92, 1927; now out of print). 



The important native tree species 

 of Alaska and Canada are also here in- 

 cluded, 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 Cana- 

 dian species in this list are almost 

 three-fifths of the 150 native tree spe- 

 cies 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 sepa- 

 rated into two lists, eastern and west- 

 ern, 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 west- 

 ern because there are more commer- 

 cially 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 ap- 

 proved common and scientific names 

 are those officially accepted and widely 

 used. Other lumber names and com- 

 mon 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 dis- 

 tribution and limits, insufficient bo- 

 tanical exploration in some regions, 

 lack of compilation of numerous 

 herbarium and published records of 

 range extensions, and difficulties in 

 mapping scattered and isolated sta- 

 tions. 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 com- 

 pared with drawings and descriptions, 

 the maps indicate which species are 

 native in a particular region and which 

 are not to be expected there. How- 

 ever, many species have been planted 

 beyond their native ranges and often 

 have spread by escaping from cultiva- 

 tion. 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. 



