ROTATION FOR QTJA^NTITATIVE EXPLOIT ABIITTT . 93 



cubical' contents of the standing wood, add thereto the contents of 

 the trees that have disappeared whether from natural causes or by 

 the hand of man, and divide the total' thus obtained by the number 

 of years expressing the given age. Tlie quotient 'is the mean annual 

 production o-f the soil at that age: The age at which this mean 

 is highest would be that of the Quantitative Exploitability of the 

 forest. But to carry out a complete series of experiments of this 

 nature would require perhaps a hundred years, and the Am^nagiste 

 could not obviously afford to wait so long; It is of course a good 

 thing to undertake them whenever the history of the forests or 

 portions of forests concerned is accurately known.^ But it is not 

 everj forest that offers such convenient data, and the general solu- 

 tion of the problem has still to be provided for. The Am^nagiste 

 must ascertain somehow or other the mean annual production of 

 the forest h^ has to organise. We, therefore, give another method 

 for obtaining this mean. 



Instead of watching the progressive development from year to 

 year of the same crop, we look out for crops growing under identical 

 conditions but of different ages. Such crops can of course always 

 be found and they enable us to obtain at once all the data we 

 require. We have thus only to ascertain for each crop its age, the 

 contents of the standing material and the quantity of produce to 

 be thinned out before it reaches the age-class next above its own. 

 We thus obtain for any given crop the total cubical contents per 

 imit of area, say per acre ; and this divided by the number of years 

 which expresses the age, gives us^ the mean annual production at 

 that age, and, as before, the age which corresponds to the highest 

 mean is that of Quantitative Exploitability. For example, the mean 

 annual production is, say, 103 cubic feet at 20, 175 cubic feet at 40, 

 210 cubic feet at 60, 220 cubic feet at 80, and 215 cubic feet at 

 100 years ; then the rotation which corresponds to the Quantitative 

 Exploitability of the forest in question would be about 80 years. 



In selecting the trial crops referred to in the preceding para- 

 graph, we must be careful that they are as complete as possible, 

 since they are supposed to represent the maximum production of 

 the soil at the respective ages. Besides this, in point of fertility, 

 they should represent the average conditions obtaining in the 



(1) This is prescribed in Forest Department Circular No. 145. 



