32 SEEDING AND PLANTING 



gravelly and shallow soil with little organic matter and with 

 little or no litter suggests an insufficient supply of these ma- 

 terials. 



The soil is the chief controlling factor not only in determining 

 the distribution of trees within their natural range, but also in 

 determining their growth and development. The soil provides 

 both the water and nourishment and, consequently, controls 

 nearly every important physiological process. It is to the 

 quality of the soil that we look for rapidity of growth, length 

 of life, form of bole and crown, and the relative abundance 

 of reproduction. It also influences the quality of the wood 

 and the yield and affects tolerance and the resistance to in- 

 jury. 



18. Water Content in Its Relation to the Choice of Species. 

 - The amount, distribution and variation of the available water 



in the soil is perhaps the most important consideration in the 

 selection of species for any particular site. Gayer l goes as far as 

 to say that the quality of the site for the growth of timber de- 

 pends solely upon the amount of available moisture. There 

 is, however, great variation in species as to the amount of 

 available water required. Distinction must be made between the 

 physical water content of the soil and the available water, as it 

 is only the latter that can be utilized by the tree. Thus, roots 

 take up much more water from the soil when it is relatively pure 

 than when it is charged with various salts and organic acids. 

 Most species when seeded or planted on alkaline or peat soils, 

 even when the physical water content is high, have difficulty in 

 absorbing sufficient moisture for growth and development due 

 to the effect of the saline or acid condition of the soil water upon 

 osmotic processes (Fig. 10). 



19. SITES WITH NON-AVAILABLE MOISTURE. If we exclude 

 sea beaches, alkaline soils, and peat soils, there are few sites where 

 the soil water is so charged with materials in solution as seri- 

 ously to interfere with the ready absorption of water by the roots. 

 Coniferous species are particularly sensitive to soils highly charged 

 with saline matter. Many species are more or less resistant to 

 acid soils, as is the case with larch, most of the cedar tribe, and 

 some spruces and pines. Many hardwoods are fairly resistant 

 to saline soils, while, as a whole, they are less resistant to acid 



1 Gayer, Karl: Dcr Waldbau. 4. Aufl. Berlin, 1898. 



