158 THE STUDY OF PLANT COMMUNITIES * Chapter VII 



fers occur principally in association with forest regions, while the 

 pedocals do not support forests but are typically covered with 

 grassland or desert. 



Pedalfers.— Although mature soils lying east of the line marking 

 the western boundary of the prairie are usually of this type, they 

 vary considerably. The range of temperatures within the area is 

 so great that podsolization is characteristic in the north and lat- 

 erization in the south with intermediate conditions represented 

 between. The following zonal climatic soil groups, therefore, 

 occur in eastern North America. 



Tundra Soils : Far northern soils with shallow profiles and 

 high proportions of undecomposed organic materials. 



Podsol Soils : Northeastern United States and extending 

 north and northwestward into Canada. Distinct horizons with 

 a thick Ao, white or gray leached A over a brown B horizon 

 with its accumulation of aluminum and iron. 



Gray -Brown Podsolic Soils : A wide band across east-cen- 

 tral United States. Like podsol but with thinner Ao horizon 

 and less leaching of the A, which is grav-brown over a brown 

 B horizon. 



Red and Yellow Soils : Southeastern United States where 

 humid, warm climate produces both podsolization and later- 

 ization. Colors bright, low in organic matter, high in clay, 

 strongly leached. Yellow soils in the sandy, poorly drained 

 coastal plain; red soils in the well-drained Piedmont. 



Prairie Soils .'Western margin of the pedalfers. Intermediate 

 between forest and grassland soils. Black or dark brown with 

 brown subsoils that differ little in texture from the surface. 



Lateritic and Laterite Soils : Subtropical and tropical. Rep- 

 resent extreme in mineral weathering. Leached of silica. 



Pedocals.— Zonation of these soils from north to south has not 

 been recognized as for pedalfers. Moisture being more effective 

 than temperature in producing variation in pedocals, the con- 

 spicuous zones lie in a north-south position. Their location and 

 brief characterization follow : 



Chernozem Soils : A broad band extending from Canada 

 into Mexico just west of the Prairie Soils. Rich in organic 



