Yearboo^ of Agriculture 1949 



n 



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Graphic relation between equal-aged yellow-poplar and subsoil in the same planting. 



Soils affect forests much as soils affect 

 any other crop. Dry soils in the hard- 

 wood belt are likely to have dry-site 

 oaks, like scrub oak, blackjack, and 

 scarlet oak. Moist soils support such 

 species as yellow-poplar, beech, maple, 

 black walnut, and red and white oaks. 

 Wet soils are more favorable for syca- 

 more, cottonwood, redgum, pin oak, 

 and willow. 



Four general soil conditions in- 

 fluence forests through their effects on 

 available soil moisture : Surface poros- 

 ity, subsoil density, aspect, and depth. 

 The first affects rate of water absorp- 

 tion; the second, free movement of 

 water in the soil; the third, surface 

 evaooration rate; and the fourth, the 



volume of water available. Surface 

 porosity is an ever-present and indis- 

 pensable attribute of the forest soils. A 

 forest soil always develops porosity 

 under a protective litter cover. This 

 porous surface facilitates absorption. 



Water movement is governed by sub- 

 soil density : The denser the subsoil, the 

 slower the movement of water through 

 it. Furthermore, the shallower the A 

 horizon above a tight subsoil, the less 

 rainfall the soil absorbs because of the 

 smaller volume of porous surface soil. 



Aspect and exposure influence avail- 

 able soil moisture by affecting the rate 

 of evaporation. South- and west-facing 

 slopes normally have less soil moisture 

 than north and east. In hilly or moun- 



