HERMAN H. CHAPMAN 69 



Current Growth of Stands. 



But it is possible to determine the present rate of 

 growth or current growth of any stand. To do this the 

 present stand is measured, to find the number of trees in 

 each diameter class. Then the width of the last ten rings 

 should be measured on several trees of each class. This 

 can be done by making a slight notch in the tree or by 

 the use of an instrument designed for the purpose, known 

 as an increment borer. This will give the size of the tree 

 ten years ago, at breast high. The volumes of the present 

 tree and of the tree ten years ago, can be taken from a 

 volume table, and the difference gives the growth in ten 

 years. From this the growth of the whole stand in that 

 period is easily determined. One way of overcoming the 

 difficulties of predicting growth for long periods is to 

 measure the crown space occupied by a dominant tree, 

 and find its age and volume. "We can assume with some 

 degree of safety that an acre will grow as many trees of 

 this size as there is room for the crowns. So difficult is the 

 general problem of prediction of growth for long periods 

 in our wild forests, that very few reliable figures exist 

 which give yields per acre. 



Growth of Individual Trees. 



Most of the studies of growth have been made to show 

 how fast the trees of a given species grow in diameter. 

 Growth studies of this kind bring out many interesting 

 facts if trees growing under different conditions are kept 

 separate. The comparison of the rate of growth of spruce 

 in old fields where it has full light, and the spruce grow- 

 ing under poplar, shows an astonishing difference in favor 

 of the old field spruce. 



Most figures on growth are shown by means of curves 

 in which the increase in size, either diameter, height or 

 volume, appears graphically by plotting the quantities on 



