TREATMENT OF SEEDING AND PLANTING SITES 189 



a. Excess of soil moisture. 



b. Aridity. 



c. Impervious subsoil. 



d. Excess of organic matter. 



e. Instability. 



3. EXCESS OF SOIL MOISTURE 



Some species thrive on moist, or even wet, soils. Most species 

 do best on fresh soils. Species acceptable for seeding and plant- 

 ing do not thrive in stagnant water. When there is an excess of 

 soil moisture over that best suited for the species, successful re- 

 generation requires the construction of works for its removal be- 

 fore the regeneration is begun. The removal of excess water can 

 be accomplished by a system of drainage or by its diversion. 1 

 Swampy ground is always difficult and expensive to handle in arti- 

 ficial regeneration. When the excess water cannot be removed 

 advantageously by diversion or drainage, the only alternative is 

 to throw up mounds or ridges upon which the seed or plants are 

 introduced. 2 In European practice, heavy limestone and clay 

 upland soils are often ditched before artificial regeneration is 

 begun. Not only is the regeneration more easily attained, but 

 later growth is more rapid and the trees less subject to disease. 



Drainage and diversion of water should be done with reference 

 to their effect upon the surrounding woodland, because any 

 radical change in the ground water during the life of the stand 

 usually results in serious injury. 



4. ARIDITY 



Overarid sites due to climatic conditions can be reclaimed by 

 irrigation. In forestry practice in the United States, irrigation 

 is employed chiefly in the nursery. In the semiarid regions 

 of the West, from Wyoming south to Texas and from Colorado 

 west to California, limited areas are artificially watered for the 

 growth of forest trees. For the most part, however, trees are 

 grown along irrigation ditches, the adjacent fields being used for 

 agricultural crops. Various species of Eucalyptus are grown 



1 Schlich, Wm.: Manual of forestry, vol. II. London, 1910. 



2 Gayer, Karl: Der Waldbau. 4. Aufl. Berlin, 1898. 



