YIELD OF EVEN-AGED HARDWOOD STANDS. 



33 



figures given are approximately accurate for stands whose basal area 

 does not vary from the average for a given age by more than 10 per 

 cent, but must be modified if applied to stands outside of this range. 



The number of trees per acre varies greatly even in fully stocked 

 stands of the same age. The number, of course, diminishes as the 

 trees grow larger. This decrease is very rapid during youth, when 



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Fig. 2.— Basal area per acre, in square feet, for three quality classes, chestnut type. The heavy lines 

 represent the average for each quality. The pairs of broken lines, united by braces, include a range of 

 20 per cent from the average, within which plots were considered to be normally stocked. 



competition is keen, but gradually lessens as the surviving trees 

 approach maturity. Since growth is more rapid and competition 

 more keen in good sites than in poor ones, the number of trees is 

 less and their size greater in quality I than in quality III stands of 

 the same age and type. The average number of trees per acre and 

 the corresponding average diameters at different ages are shown in 

 the yield tables. 



23329°— Bull. 96—12 3 



