THE EED SPRUCE. 
41 
Hampshire would undoubtedly show somewhat better general de- 
velopment there than in Maine. 
The growth in volume of trees in even-aged stands may be deter- 
mined in a manner similar to that just described. In this case, how- 
ever, the diameter growth instead of being calculated by arbitrary 
periods, such as 10 or 20 years, would be expressed in terms of total 
age. If the rate of volume growth is to be determined for natural 
stands undisturbed by thinnings or other treatment winch would 
tend to interfere with the process of elimination by natural competi- 
tion, the diameter growth should be based on the average growth of 
all green trees of the even-aged normal stands of different ages. If, 
however, thinnings are contemplated which will enable the trees com- 
posing a stand to grow at their maximum rate with the minumum 
of competition, the basis for growth should be the mean average of 
the dominant and intermediate (Table 12) or, under the most favor- 
able conditions, the dominant trees only of the even-aged normal 
stands of different ages. 
STANDS AND YIELDS. 
The yield of virgin or selection growth spruce, both present and 
future, varies widely from one type to the other and within the same 
type in different regions. It is not possible under the circumstances 
to discuss the subject in such detail as to cover the full range of 
conditions which local variations impose, nor are the data available 
for such discussion. Given certain fundamental data, the range of 
reliability of which is less restricted than would be yield tables based 
on the widely variable conditions existing in our present virgin and 
cull spruce selection forests, the yield for any particular tract can 
be readily computed. 
Aside from that already presented for the various regions under the 
headings of growth in height, diameter, and volume, the only infor- 
mation needed is the enumeration of the stands 1 the yield of which is 
to be determined and their average composition as to size and species 
calculated and tabulated for use in the following convenient form: 
Diam- 
eter, 
breast 
high. 
Average number of trees. 
Spruce 
left to 
grow 
(average 
number). 
Spruce. 
Other 
species. 
Total. 
1 
2 
3 
4 
5 
Inches. 
I 
1 In the appendix (Tables 50-53, inclusive, on pp. 94-97), will be found stand tables prepared from such 
enumerations in virgin forest growth of the spruce slope type. The associated species are included as a 
matter of comparison. Incidentally, these tables show in a broad general way the relative production 
per unit of area of the different regions which they represent. It must not be understood, however, that 
any claim is made that they show exact average conditions throughout their respective regions. 
