202 
Indian^ Forest Records. 
ti 
[VOL. I. 
advocated ; and it is likely that the last will yield a more correct indica- 
tion.* Pending a solution of the question, Yield Tables, as at present 
prepared, show per unit of area the number of stems, the mean height 
and diameter, the basal area and the volume of normal woods of differ- 
ent ages according to quality classes ; and statistical data relating to 
each of these factors must be collected. 
Turning now to the species under investigation it must at once be 
noted that no such tables can at present be prepared for the Sal in India, 
since the absence of even-aged woods, and the wholly abnormal condi- 
tion of the majority of the Sal woods under systematic management ren- 
ders the collection of sufficient statistical data impossible. Neverthe- 
less it is probable that in certain Divisions a beginning can be made in 
studying some of the factors which find a place in the Yield Table. 
In the United States of America, so-called Yield Tables are prepared 
for uneven-aged woods to show the future yield of many-aged stands at 
different periods after a portion of the trees have been cut under a speci- 
fied method of selection. In other words, the tables under consider- 
tion contain the merchantable yield per acre of a given species before the 
selection cuttings, and the prefficted future yield in 10, 20, and 30 years 
after cutting : the tables being based on the assumption that the timber 
will be cut to a specified diameter limit. f Such tables depend wholly 
on the correct calculation of the percentage of stems that are likely to 
survive to pass from one girth class to the next ; on the rate of girth or 
diameter increment ; and on the volume of the mean tree of each girth 
class — questions which are dealt with in different parts of this Note . 
Section 2. — Number of Stems per Acre. 
Laws which govern the development of the density of stems in even- 
aged woods in general : — 
1. At an early age in crowded woods, the number of stems per acre de- 
creases very rapidly year by year. 
ll. The rate of diminution, which is faster in favourable locahties, decreases 
as the wood ages : but never ceases as long as the trees continue to 
grow. 
ill. In mountain forests, the number of stems per acre increases with eleva- 
tion above sea level.J 
The number of stems per acre is liable to greater and more arbitrary 
variations than any other factor coimected with the development of 
* See also Schlich’s Manual ; Vol. Ill, page 97. 
I Forest Mensuration by Henry Solon Graves. The method is similar to that usual- 
ly employed in India for estimating the yield of selection-worked Sal and Teak forests. 
J Her forstlicbe Vesuchsweseu, Gangbofer. See also Indian Forester, Vol. XIX, 
page t>. 
