Yearbook of Agriculture 1949 



forests. The western boundary of the 

 'eastern United States' as thus defined 

 is a wavy north and south line extend- 

 ing from Canada to Mexico between 

 the 97th and 101st degrees of longi- 

 tude." 



Lee R. Dice, in the book The Biotic 

 Provinces of North America, 1943, 

 recognizes 20 biotic provinces in the 

 United States, in 17 of which trees 

 are either important or dominant. He 

 defines biotic province as "a consid- 

 erable and continuous geographic area 

 . . . characterized by the occurrence 

 of one or more important ecologic as- 

 sociations that differ, at least in pro- 

 portional area covered, from the as- 

 sociations of adjacent provinces. In 

 general, biotic provinces are character- 

 ized also by peculiarities of vegetation 

 type, ecological climax, flora, fauna, 

 climate, physiography, and soil." 



The Committee on Western Forest 

 Types of the Society of American For- 

 esters in 1945 recognized and defined 



50 forest types in the western part of 

 the United States. This means that the 

 Society of American Foresters has rec- 

 ognized 147 distinct forest types in the 

 United States. Some of these, such as 

 ponderosa pine, redwood, lodgepole 

 pine, and Engelmann spruce, may oc- 

 cupy large areas in pure or almost pure 

 stands. Most of the types, however, 

 are mixed. In general, eastern types 

 are more complex than western, and 

 conifer types less complex than hard- 

 wood forests. In going from north to 

 south, the types, with some exceptions, 

 tend to a greater number of species. 



WILLIAM A. DAYTON is in charge 

 of dendrology and range-forage in- 

 vestigations of the United States Forest 

 Service. He is probably best known for 

 his publications on native range plants 

 and is joint editor, with Harlan P. 

 Kelsey, of Standardized Plant Names. 

 Mr. Dayton has been connected with 

 the Forest Service since 1911. 



FORESTS AND SOILS 



JOHN T. AUTEN, T. B. PLAIR 



Successful reforestation, particularly 

 with the hardwoods, has to take into 

 consideration selection of the proper 

 species and the balance between trees 

 and soil. Perhaps the soil has eroded or 

 all trees have been removed from it: 

 Then it is not simple to choose trees 

 that grow well on bare land; also, the 

 balance that existed in the virgin for- 

 ests was destroyed when the land was 

 cleared. Basic soil and atmospheric 

 changes often make such areas inca- 

 pable of supporting the original species. 



Soil loss from erosion following fire, 

 overgrazing, clearing, and cultivation 

 is a basic loss. It reduces productivity 

 of cleared land; it also lowers the site 

 quality in existing forests. Any appre- 

 ciable change in soil necessitates a 

 shift in species composition in order to 

 obtain those best suited to the site. 

 Site deterioration means species of 



lower value in the stand and a loss to 

 the owner. 



Accordingly, the problems of restor- 

 ing and conserving our trees and for- 

 ests will be simplified by a knowledge 

 of forest soils and of the relation be- 

 tween forests and soils. 



A soil is a natural mineral body with 

 distinct features that identify it, even 

 in widely separated areas. It has def- 

 inite structure with horizons or layers, 

 one over the other. The topsoil, from 

 which the fine soil has been washed by 

 percolating waters, is the A horizon. 

 Just under it is horizon B, the heavy 

 horizon or subsoil, which receives the 

 fine soil washed out of A. The C hori- 

 zon is the parent soil material below B. 



A fertile soil contains a myriad of 

 living organisms, plant and animal, 

 adapted to the soil conditions. It has 

 pore space, which contains water and 



