Part IV.] Caccia : Selection method of treatment in India. 395 
each other sufficiently. Thus ultimately each coupe becomes a compartment, 
just as in the regime of coppice. 
The coupes are worked successively in the order in which they follow one 
another on the ground. 
At the beginning of each rotation a complete enumeration survey is made of 
all the trees 20 centimeters (8 inches) and over in diameter. Every tree more 
than 17^^ but less than 22^ centimeters in diameter is registered as being 20 
centimeters in diameter; every tree more than 22^ but less than 27^ centimeters 
as one of 25 centimeters; and so on. The quantity of stem- wood in each of 
these diameter classes rising from 20 centimeters, 5 centimeters at a time, is 
then computed from the results obtained from the careful cubing of type stems; 
and then by addition the quantity of stem-wood in each of the three larger 
working diameter-classes (Classes Tl, III and IV) described above is obtained. 
Let this be respectively Vii, Vni and Viv 
We will suppose that the forest under consideration has been taken in hand 
for the first time, so that the rate of growth is not known. M. Gurnaud does 
not waste any time or energy in trying to ascertain it (a more or less insoluble 
problem under the condition which he postulates for the future working of the 
forest), but makes the fixing of the yield of the ensuing rotation a matter of pure 
discretion. 
Here is his method. He assumes a certain moderate figure for the percentage 
at which the annual increase has been taking place during the immediately 
preceding 6, 8 or 10 years, as the ease may be. Then with the help of these 
two figures, which we will designate respectively r and n, and of that expressing 
the standing stock of stem-wood (Vu-f Viii-fViv = say Vp) he obtains, by means 
of a simple interest sum, the stock of stem-wood existing n years ago, which 
quantity we will designate Vp 
_ 100V, 
100 r n 
Hence the current annual increment during the past n years 
^ Vp-Vn .V. 
u JOO r D 
It will be observed that it would be more correct to apply the formula for 
compound interest, and also to take into account the produce removed during 
the period in question; but, as will be seen, M. Gurnaud ’s subsequent use of 
the increment is such that the rough and ready method of calculation just 
described gives him all he wants. 
If the forest appears complete, the three working diameter-classes are well 
represented and Vp is large enough, he prescribes for the quantum of the 
annual fellings the full figure obtained as above for the current annual increment. 
But almost invariably one or more of the three hypotheses assumed are wanting, 
and he accordingly reduces the annual yield for the ensuing rotation to some 
fraction of that figure, two-thirds, one-half, one-third, one-fourth or even less. 
At the end of the first rotation he makes a fresh enumeration survey on 
the same principle as before. For the first time now he can calculate exactly 
the rnean annual increment during the past n years, for he knows the stock 
standing respectively at the commencement and at the end of that period and 
the quantity of material cut out in the meanwhile. This time again the con- 
dition of the stock may be so far removed from the normal sought as to require 
the yield during the second rotation being reduced as before. And indeed it 
may be a good many rotations before it is possible to adopt the full figure cf 
the past mean increment. Nevertheless each successive rotation will find the 
stock nearer the normal state. 
