150 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
£93,391. These figures being derived from forests covering 
131,880 acres, it follows that the average annual nett income is 
just over 14s. 1§d. per acre. In one district (Torfhaus) it is as 
low as 4s. 8d., while in another (Elend) it is as high as 28s. 6d. 
Of the 103,590 acres of spruce forest in the Upper Harz, nearly 
99,000 acres are worked as even-aged high forest, and the rest on 
the shelter-wood selection system. The latter system is practised 
only in the higher parts of the Brocken, on very steep declivities, 
and in the neighbourhood of the mines, where the smoke proves 
troublesome. The general rotation-period is now 120 years, though 
formerly it was only 100. Taking the whole forest area into con- 
sideration, it is found that the average annual out-put of timber 
amounts to about 35 cubic feet (English measurement) per acre, 
besides which, branches, tops, and small-wood produce about 
10 cubic feet. The yield of timber varies considerably in the 
various forest divisions, being as low as 20 cubic feet in Torfhaus, 
and as high as 46-cubic feet in Osterode. Under favourable cir- 
cumstances the spruces at 100 to 120 years of age attain a height 
of 120 feet, and at the final felling furnish 6500 cubic feet of timber 
(English measurement) per acre. In the higher districts, however, 
where many of the trees have lost their tops through snow- 
breaking, and where the conditions of growth are altogether less 
favourable, the yield will not exceed 2500 to 4000 cubic feet ; 
while near the upper limit of tree growth the yield will seldom 
exceed 700 or 800 cubic feet. 
Where the woods are managed on the even-aged high forest 
system, it is the custom to clear off the whole of the trees at the 
end of the rotation. Care is taken, however, not to make any 
single clearing very large. In order to guard against the 
attack of the pine weevil, a clearing is never undertaken in the 
neighbourhood of a young wood, for were such done the beetles 
would increase rapidly in the old stools, and afterwards move on 
to the young wood. When an area has been cleared, the stools 
are rooted out as quickly as possible, and after lying bare for three 
or four years the ground is restocked. 
The shelter-wood selection system consists in the removal of 
mature trees wherever they occur in the wood, and it is expected 
that the seed naturally shed by adjoining trees will furnish plants 
enough to fill up the blanks. In this way it is evident that an 
uneven-aged wood will result, that is to say, we shall have trees of 
all ages growing irregularly throughout the wood. It sometimes 
happens that the desired object is not attained, in which case 
assistance has to be given by means of seed artificially sown, and 
even in some cases by the insertion of young plants. This system 
is only practised where it is undesirable to completely clear an 
area, such a case occurring, for instance, on a steep declivity with 
