146 OUR FORESTS AND WOODLANDS 
average annual growth in height reaches about 
fifteen inches on favourable situations, and even 
increases to about nineteen inches among the 
predominant poles of twenty to thirty years of 
age. On soils of a less favourable character the 
growth is of course less, while it does not reach 
its maximum till from ten to fifteen years later. 
The thick fall of leaves, rich in potash, yields the 
finest class of woodland mould, so that at this 
stage of growth dense thickets of beech enrich 
and improve the soil in a greater degree than any 
other crop can. Stimulated thereby, the growth 
in cubic contents proceeds so vigorously that 
pure beech highwoods, on soils of only average 
quality, yield over 8000 cubic feet (true measure- 
ment) per acre; but, unfortunately, only from 10 
to 20 per cent. of this is usually classifiable as 
first-class timber, the bulk of it being too small 
for reckoning as such. 
