A METHOD OF INVESTIGATING YIELDS PER ACRE IN 

 MANY-AGED STANDS. 



By Herman H. Chapman. 



A crop of timber is the total quantity of material which can be 

 grown on a definite area in a given period of time. The three 

 factors involved are volume, area and age. When stands of 

 timber are even-aged and fully stocked, yields can be determined 

 quite simply by laying ofif plots, measuring the contents of the 

 timber, and cutting a tree or two to get the age of the stand. 

 Such figures or yield tables give the only scientific basis for de- 

 termining the productiveness of forest land, for fixing the length 

 of the rotation and solving important problems in forest valuation. 



Unfortunately, a large proportion of our native forest areas do 

 not permit of the use of this method. Age classes are inter- 

 minged in such an irregular manner, that it is difficult to lay out 

 even small plots with any assurance that the timber so included 

 will be of the same age. Under these circumstances the method 

 has been to fall back on a study of current growth, based on 

 diameter, and by determining the growth for 5 to lo years in 

 board feet, or even by growth per cent., draw conclusions as to the 

 probable yield per acre. That this method is unreliable and a 

 misleading makeshift must be evident from the well-known rela- 

 tion between current growth and mean annual growth, namely 

 that the former diminishes for some time before the latter has 

 culminated. 



Nor will the mere study of growth of trees as individuals, 

 suffice to prove the yields that can be expected on an acre. The 

 number of trees which can grow on an acre differs too much with 

 age and has too great an influence on yields to be ignored in this 

 manner. 



In studying the relation of production to age it is worth bearing 

 in mind that growth is the result not of mathematical laws but of 

 natural forces. The determination of the amount of space in 

 square feet which a tree is actually occupying at various ages is 

 the fact upon which the yield per acre hinges. If we could get at 

 this one fact for average trees of different ages it would go far 

 towards solving the whole problem. 



