PHYSIOGRAPHIC FACTORS 



145 



Fig. 74. Wind-swept alpine habitat in Utah with typical coarse, angular 

 soil particles and little organic material. Krummholz at left is of Picea en- 

 gelmanni and Pinus flexilis (see also Fig. 47).— U. S. Forest Service. 



soil about exposes new particles to chemical action and likewise 

 helps to incorporate organic matter. 



The chemical or decomposing processes all tend to result in in- 

 creased solubility of soil materials, which, in solution, may then be 

 available for the use of plants but are also subject to leaching, or 

 washing out, of the surface layers by rain water. Both oxidation 

 and hydration, the addition of oxygen or water to a compound, 

 are common and result in softening of rock. Carbonation, or the 

 taking up of carbon dioxide, produces carbonic acid merely by 

 union with water, and the acid is an effective solvent of many 

 rocks. Water itself is a weak solvent, and, with the addition of 

 carbonic acid, which is always present, its action is much increased. 

 Decaying vegetation, when present, also contributes acids that 

 facilitate solution. In solution, salts ionize and the relative effective 

 concentrations of the basic and the acid radicals thus formed de- 



