io6 OUR FORESTS AND WOODLANDS 



thinnings of the young woods should be carried 

 out with special reference to the oak. No definite 

 rule can be framed as to the time when this 

 operation becomes necessary. On some soils 

 the poles complete their main growth in height 

 as early as the fortieth to the sixtieth year, while 

 in other cases this condition is not attained till 

 perhaps the seventieth or eightieth year. Except 

 where actually filling spaces that would other- 

 wise be blank and unprofitable, softwoods like 

 birch, aspen, and willow should be cut out in 

 favour of hardwoods of any kind, while the latter 

 should be removed wherever they interfere with, 

 and threaten to impede or altogether suppress, 

 the growth of the oak. Only thus can the 

 oak, the ultimate crop desired, maintain itself 

 in advance of the other competitors for light 

 and air, many of which often show themselves of 

 somewhat speedier growth, and therefore likely 

 to outstrip it in the struggle upwards for supre- 

 macy. This war of genera the * struggle for 

 existence' observable everywhere as one of the 

 great laws of nature is nowhere more clearly 

 noticeable than among the trees of the forests 

 and woodlands. 



