STOCKING THE GKOUND 127 



of humus on top of the mineral soil, from which water 

 carries the plant foods in solution to the roots of the 

 trees. 



Under a light-foliage crop, however, too much light 

 is admitted, and the leaves are dried up and do not 

 decay. The soil therefore deteriorates, and in time 

 becomes so poor that the trees cannot obtain sufficient 

 nutriment. To improve and protect the soil for the 

 benefit of a proportion of the trees, the crop should be 

 heavily thinned, leaving only the best stems, to the 

 number of about 300 to 350 per acre for Oak at 50 years, 

 and 350 to 400 per acre for Larch or Scots Pine at 25 to 

 30 years; and shade-bearing trees introduced as an 

 undercrop to improve the soil. 



Beech is by far the best tree for the purpose, as it not 

 only bears shade well, but its leaves contain a greater 

 percentage of plant foods than those of any other tree. 

 Hornbeam comes next as a soil-improver, while Silver 

 Fir, Spruce, Sitka Spruce, Douglas Fir, are splendid soil- 

 protectors. Wey mouth Pine and Thuja gigantea are also 

 often used with success. 



These trees may all be notched or dibbled in, as they 

 will have the protection of the older crop and the ground 

 will be fairly clean. Underplanting will not only improve 

 the soil and stimulate the growth of the overcrop, but, 

 if not left till too late, will help to keep the trees from 

 becoming too branchy. 



The time to underplant is when a falling off in incre- 

 ment is noticed. Underplanting, too, is used as a method 

 of repairing the ravages of the Larch disease. 



