158 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
average yield during the last 25 years has been about 168,000 
cubic feet actual contents (or about 130,000 cubic feet square- 
of-quarter-girth measure) per annum, which corresponds very 
closely with the above estimate ; while during the last 10 years 
the gross annual income has averaged about £2700, and the 
expenditure £2250. ‘This leaves only about 2s. 1o}d. per acre as 
the net annual return from the capital invested in the timber-crops 
and the soil, which is, of course, only a small fraction of what 
could easily be obtained from a purely sylvicultural management 
on business principles. But everything is done to render the 
woods as pleasant as possible to visitors during the spring, 
summer, and autumn seasons, hence even all kinds of work in 
the woods is accomplished, so far as possible, between October 
and April, when labour is scarce and dear, and the days are 
short. 
There is little or no total clearance even of old, over-mature 
crops growing on soil that has become deteriorated, as even in 
such case very gradual clearance round the edges is preferred, 
with planting to supplement or take the place of natural regenera- 
tion. And the same is done with the younger conifer crops of 
backward growth, such as those about 50 years of age and only 
30 to 4o feet in height, as experience has shown that even free 
thinning does not enable the trees to recover energy of growth 
and beauty of form. Sporadic felling in small patches is the 
rule; and unless there are self-sown family groups that can grow 
up satisfactorily in the freer exposure to light and air, the blanks 
thus formed are filled by planting. And the result of this sort of 
treatment is to produce mixtures of many kinds of woodland 
trees, sometimes occurring pure in patches of varying area, or 
else forming mixtures in which different kinds of trees are inter- 
spersed either merely as scattered individuals, or else in groups 
of varying size and age. 
Such open woods are always more exposed to damage from 
wind than crops standing in closer canopy, consequently wind- 
fall or damaged trees are numerous, and these must be speedily 
cleared to avoid the danger of forming breeding-centres for 
noxious insects. Another result of the wider distance than usual 
from stem to stem is the fact, of particular interest to the British 
forester, that the soil is often thickly overgrown with a dense 
tangle of rank weeds. In many places there is, even under the 
heavy shade of spruce, a thick undergrowth (consisting here 
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