186 OUR FORESTS: AND WOODLANDS 
to become much broken in canopy, and then 
the best thing is to thin out the plantation 
and underplant the birch with some sort of 
tree like spruce, or whatever promises to be a 
remunerative crop on land of the given descrip- 
tion, the standards being removed whenever the 
best financial moment seems indicated by con- 
sideration of the state of the underwood. In 
general, birch will have reached its maturity 
between the age of forty to sixty years. 
The best development of birch and aspen is 
attained when they are grown along with alder 
or hornbeam in moist places, or with pine on 
drier situations. Where they are found thriving 
in pure woods, it may be safely asserted that 
other crops of timber could be grown there with 
greater profit to the owner. This remark cer- 
tainly applies to parts of Scotland, as in Perth- 
shire, where open woods of the birch are very 
often to be found. 
One drawback, not a very serious one, it is 
true, but still a disadvantage, of having birch 
and aspen growing along with, or even in the 
vicinity of, Scots pine or larch, is that two forms 
of fungous diseases not uncommon on these latter 
