260 OUR FORESTS AND WOODLANDS 
retained in the woods so long as actuarial cal- 
culations (for which the rate of growth shown 
by the trees themselves and the local market 
prices afford the only practical data) show that 
the woods are still in full vigour, and that the 
increment being annually made (judged by its 
equivalent under the monetary standard) is not 
already beginning to diminish. 
Experience shows that in highwoods the 
longer periods of rotation prove advantageous 
on the better classes of land, while in copse 
and in coppices the shortest periods are only 
permissible on good soils and favourable situa- 
tions. That is to say, on the better classes of 
woodland soil highwoods can be profitably grown 
with a longer rotation than on poor land; while 
in copse and coppice the fall can be repeated all 
the more frequently the better the quality of the 
land, because there is not the same danger of 
deterioration by frequent exposure. 
Unfortunately, no average data on any large 
scale are as yet available from British woods 
to prove these facts, though they are matters 
of common experience in practice. In default 
of such statistical tables for Britain, it may 
