BRITISH FOREST TREES 



43 



and growth in girth. It is a convenient measure of the 

 general energy of growth, expressed either by the quantity of 

 timber of a given species produced on a given area within a 

 given period, or by the time necessary to produce a given 

 quantity of timber of any particular species on a given area. 

 From the sources already mentioned on page 36 the 

 average total number of stems per acre is calculated to be : 



The average cubic contents of the entire individual tree 

 grown in pure forests and in close canopy have been found 

 to be (in cubic feet) : 



