CHOICE OF SPECIES IN ARTIFICIAL REGENERATION 33 



soils. The average moisture condition of the soil is not indicative 

 of its capacity for supplying any particular species with moisture, 

 as the requirements vary at different periods of the year. The 

 available moisture at the driest period of the growing season is 

 much more important. 



FIG. 10. Poor form and growth in a plantation of Scotch pine due to 

 acid soil. Adirondack Mountains. 



20. OPTIMUM DEVELOPMENT AND AVAILABLE MOISTURE. - 

 Species vary greatly as to the amount of available water neces- 

 sary for optimum development and in their resistance to a falling 

 off from this amount. In general, a decrease in the amount re- 

 quired for optimum growth and development causes a very rapid 

 falling off in height growth. Surface-rooted species are more 

 sensitive to drought than deep-rooted ones owing to the greater 

 variation in the moisture conditions of the surface soil. White 

 ash, black walnut, tulip, beech, hard maple, and black cherry are 

 very exacting and deteriorate rapidly when planted on sites where 

 the available moisture falls much below that required for optimum 

 growth. On the other hand, red pine, white pine, and hemlock 

 are far less exacting and make acceptable growth when seeded or 

 planted on soils much drier than those required for optimum 

 growth. 



