106 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. 
