REPRODUCTION OF WESTERN YELLOW PINE. 31 



divisions is from the same source and the divisions are essentially the same 

 in chemical character. All of the soil is essentially the same in the physical 

 nature of the profile or succession of separate horizons. The divisions shown 

 on the map are for the most part soil phases rather than types since they are 

 based merely upon small differences in thickness of the soil layer, and in 

 amount of stone and gravel which may be either on the surface or incorporated 

 in the soil. The soil of the plot as a whole is fairly representative of what is 

 probably the most extensive soil site in the yellow pine forest in the Tusayan 

 and Coconino National Forests. 



Soil No. 24. 



description of soil profile. 



Surface soil dark reddish clay loam or clay, underlain by a somewhat stiffer 

 and more compact red clay at 4 to 6 inches ; this extends to depth of 18 inches 

 to 3 feet, becoming a lighter shade of color and more friable at base because of 

 the increased stone and gravel content. The soil layer rests upon solid bed- 

 rock of basalt or upon reddish coarse fragmental blocks of somewhat scoriace- 

 ous basaltic lava. Generally a small amount of fragments of gravel size and 

 smaller per cent of stones are scattered over the surface and incorporated in 

 the soil. The humus content is low. The soil is mainly residual. 



RELATION TO YELLOW PINE AND VEGETATIVE CHARACTER. 



Soil layer thin, clay difficultly permeable and root development circum- 

 scribed. Where plant mold from grasses is absent, the surface clay tends to 

 become hard and compact. Conditions for germination and survival not as 

 favorable as on soils 6 and 12. Fairly dense cover of Festuca arizonica and 

 Muhlenbergia montana. 



Soil No. 6. 



soil description. 



Surface soil moderately friable, reddish-brown clay loam underlain at about 

 6 inches by stiff red clay. Similar to soil 24, but on the average less in thick- 

 ness, while stones are scattered more freely over the surface, constituting 

 probably 50 to 75 per cent of the total surface area. More humus and a more 

 loamy surface soil than that of 24. The bedrock is generally impenetrable for 

 tree roots. 



RELATION TO YELLOW PINE GROWTH. 



Soil is favorable for germination and survival. Root development circum- 

 scribed, and increment would not be expected to be as high as on soils 9 and 20. 



Soil No. 12. 



soil description. 



The areas numbered 12, characterized by rock outcrop and detached boulders 

 projecting from a few inches to 2 or 3 feet above the surface or soil line. 

 Seventy-five to 95 per cent of surface area occupied by rock. Greater accumu- 

 lation of litter and humus at surface than on other types producing a more 

 friable or loamy soil. Soil covering very thin, consisting for the most part 

 merely of a few inches of humus soil resting upon the rock, but in places a 

 stony red clay subsoil is present in the deeper pockets. 



