444 CURRENT OR PERIODIC GROWTH OF STANDS 



or current annual growth. A forest resembles more closely a many- 

 aged stand than one composed of a single age class. In such a stand 

 or forest, it is not possible to separate one period which coincides with 

 the complete cycle of production for a crop of timber, as can be done 

 in the even-aged stand. The total production of the many-aged area 

 or of the forest, for a period equal to that required to grow one crop 

 from seed to maturity, may equal that of the even-aged stand, but it 

 is laid on in many stands. 



In a regular many-aged forest the current growth for one year is 

 the growth in volume of each stand, including those which are as yet 

 unmerchantable. This is true of the forest, whatever its form. The 

 current growth on the mature timber is but part of the total; that which 

 represents the younger stands is equally important. Growth is not 

 usually measured, on either trees or stands, until a size is attained which 

 is merchantable for some form of product. Another reason for post- 

 poning the measurement of young stands is that a very large per cent 

 of the existing trees in such stands will never reach maturity, and the 

 total volume at any period previous to an age at which it can be used 

 is misleading and serves no useful purpose, while by contrast the natural 

 selection of surviving trees in stands measured at merchantable age 

 has already occurred and the results are accurately gaged. 



When the volume is finally measured on a young stand for the first 

 time, it represents the growth for the entire preceding period. Perhaps 

 but 10 per cent of the trees are large enough to measure at this time. 

 After another decade, the stand is again measured. By this time 

 50 per cent of the trees may be merchantable. The growth for this 

 decade now includes the current growth, for ten years, on the original 

 10 per cent, plus the growth since germination on the remaining 40 

 per cent. At the third measurement, all trees which survive may be 

 merchantable and are measured, but a portion of them have entered 

 the merchantable class^ after being missed for the two previous decades. 

 What happens is that although current increment by decades is sought, 

 yet for trees which mature and are measured for the first time, total 

 growth is substituted for current growth since there is no other way 

 to handle it. 



If this example is now applied to a forest composed of a series of 

 even-aged stands, the same thing is seen to occur. For the forest, 

 the current increment is the increase in merchantable cubic volume 

 of stands already partly merchantable; but to this is added, in each 

 decade, stands measured for the first time, whose volume though added 

 as current increment is in reality the total gi-owth of several periods 

 instead of one. It follows that for a stand just becoming merchantable, 

 the apparent current growth will be very rapid during this process 



