162 FOKESTEY WOEK 



by the number of trees on the area, which gives the total 

 number of cubic feet. 



In the third method, sample plots from \ an acre to 

 3 acres in extent are measured off, the trees counted, the 

 average stem for each plot found, and the figures per acre 

 arrived at from these. 



This method is best where the growth of the trees varies 

 in different parts of the wood. 



If the crop is mixed, the contents of the different species 

 must be calculated separately. 



Taking as an example a mixed wood of 40 acres con- 

 taining, say, 600 poles per acre, or 400 of which are 

 Larch and J or 200 Corsican Pine. The average Larch 

 pole is found to contain 6 cubic feet, and the average 

 Corsican Pine 8 cubic feet. Thus there are 2,400 cubic 

 feet of Larch and 1,600 cubic feet of Corsican Pine per 

 acre, and 96,000 cubic feet of Larch and 64,000 cubic 

 feet of Pine on the whole area. 



Also, if the growth or density of the crop varies much 

 in different parts of the area, estimates should be made 

 for each class or density. The best method of finding the 

 average pole is by Weise's 40 per cent. rule. The poles 

 are counted on each sample area and the J girth 'or dia- 

 meter taken at breast height (viz., 4 feet 3 inches). The 

 measurements are divided up into inch classes, and the 

 number for each class totalled up. Thus, if a sample area 

 of 1 acre contained, say, 200 trees divided into 1-inch 

 classes, they would be tabulated as in the first two 

 columns of the following table: 



