Forest Types of the United States 



type is a forest type now occupying the 

 ground, no implication being conveyed 

 as to whether it is temporary or per- 

 manent." 



Raphael Zon, in Principles Involved 

 in Determining Forest Types, pub- 

 lished in 1906, emphasizes the im- 

 portance of forest types in silvical 

 studies of individual species, and sets 

 forth a philosophy basic to determin- 

 ing forest types. The main considera- 

 tions are physical conditions of climate, 

 soil, and the like; man and his opera- 

 tions ; accidents, such as fire and wind. 

 He says that "one of the most im- 

 portant characteristics of a forest type 

 is its stability, its resistance to invasion 

 by other forms," and adds that the re- 

 production of the forest must always 

 be considered. 



Arthur W. Sampson (The Stability 

 of Aspen as a Type, 1916) believes that 

 aspen is a temporary type, replaced, 

 slowly but surely, by conifers. 



Carlos G. Bates, in Forest Types in 

 the Central Rocky Mountains as Af- 

 fected by Climate and Soil, 1924, states 

 that, in a general way, the forest zones 

 of that region correspond with air- 

 temperature zones. He adds that a re- 

 view of the facts leaves little doubt that 

 the tree species of the central Rocky 

 Mountains are controlled in their dis- 

 tribution almost wholly by the degree 

 of insolation of the site, with the re- 

 sultant temperatures, and by the closely 



< Adapted from Dr. James G. Cooper's 

 Distribution of the Forests and Trees of 

 North America (1859). The letters indi- 

 cate: C, Lacustrine Province (Canadian Re- 

 gion); D, E, F, G, Apalachian Province 

 (Alleghany, Ohio, Tennessean, Caro- 

 linian Regions, respectively); H, Mississip- 

 pian Region; I, Floridian Region (part of 

 West Indian Province); J, K, L, M, N, 

 Campestrian Province: (1) Prairies, J 

 (Texan Region), K (Illinois Region), L 

 (Saskatchewan Region), (2) Arid Plains, M 

 (Dacotah Region), N (Comanche Region); 

 Q, Mexican Province (Chihuahian Region); 

 R, S, T, U, V, Rocky Mountain Province 

 (Arizonian, Wasatch, Padoucan, Utah, and 

 Shoshone Regions, respectively); W, X, Y, 

 Z, Nevadian Province (Californian, Ore- 

 gonian, Kootanic, and Yukon Regions, 

 respectively). 



Ill 



related surface conditions of moisture. 



A distinguished Finnish forester and 

 ecologist, Aimo K. Cajander, places 

 forest typification on a combined eco- 

 logical and biological basis (The 

 Theory of Forest Types, English trans- 

 lation revised by Mr. M. L. Anderson, 

 1926). He recognizes two kinds, in 

 principle, of forest classification, ac- 

 cording to quality and site. He says: 

 "The features of a plant association are 

 generally determined by those species 

 which are present in the greatest 

 abundance and frequency. Those spe- 

 cies, however, which are present at 

 a lesser rate of abundance, but are, 

 nevertheless, always or nearly always 

 present, are also, of course, equally 

 characteristic of the association. Fi- 

 nally those species, which, though they 

 may be more or less rare, are met with, 

 however, almost exclusively in the as- 

 sociation in question, are also charac- 

 teristic of that association. On the 

 other hand, of course, the absence of 

 certain plant species is also a very im- 

 portant feature in the delineation of 

 a plant association, although the defi- 

 nite establishment of absence is more 

 difficult." 



Arthur Freiherr von Kruedener, who 

 published Waldtypen Klassifikation 

 und ihre volkswirtschaftlich Bedeutung 

 in 1927, based scientific classification 

 of forest types on three factors: Cli- 

 mate, soil, and plant associates : "Was 

 wir unter Waldtypen verstehen, sowie 

 von den Faktoren Klima, Boden-Un- 

 tergrund und Pflanzengemeinschaft, 

 welche drei in ihrer Verbindung uns 

 erst den Begriff des Waldtyps geben." 



Gustaf A. Pearson, in Forest Types 

 in the Southwest as Determined by 

 Climate and Soil, 1931, distinguishes 

 seven broad zones with four forest 

 types: Woodland, ponderosa ("west- 

 ern yellow") pine, Douglas-fir, and 

 Engelmann spruce. The soil differ- 

 ences, he says, appear to be due more 

 to physical than to chemical differ- 

 ences, the more porous soils being best 

 suited to tree growth, the upper alti- 

 tudinal range determined by ability to 

 withstand low temperatures and the 



