factory means of estimating stocking are by total volume or by 

 basal area. Of these two, the basal-area method requires much 

 less computation and for practical purposes is as accurate. By 

 this method the relation between the actual total basal area per 

 acre and the corresponding table values for the particular site 

 and age establishes the percentage of normality of the stand. 

 No quicker or more satisfactory method of judging normality 

 than the basal-area method has as yet been found. Attempting 

 to establish normality on the basis of completeness of crown 

 cover, total number of trees, number of dominant trees, average 

 diameter, or any other easily obtained criterion is for many 

 reasons far from satisfactory. 



If the stand is normal to-day, its yield 10 or 20 years in the 

 future (but hardly longer) may be predicted from the yield 

 tables simply by adding the 10 or 20 years to the present age 

 of the stand and reading from the table the yield at that age on 

 the site as identified. 



Prediction of yield from an abnormal or understocked stand 

 is not quite so reliable. It is possible that a stand not now 

 normal tends to become normal as it grows older, but the rate 

 of progress toward normality, if any, awaits investigation and 

 at present can not be safely predicted. For this reason the 

 future yield of a stand known to be understocked at present can 

 only be conservatively predicted from the tables by assuming 

 that its present percentage of understocking will remain con- 

 stant. If a sample plot has but 50 per cent of the basal area of 

 a normal plot, all that may be counted upon 10 or 20 years 

 hence is 50 per cent of the yield shown in the tables for that 

 species and site at the ages then attained. 



For example, if it be assumed that a tract of 50-year-old 

 loblolly pine of 750 acres, variously stocked, is to be cut at three 

 different periods in the future, the situation might shape up as 

 follows : 



Number of acres 



Site 

 index 



Normal- 

 ity 



Cutting 

 age 



(years) 



250_ 



110 

 90 

 70 



90 

 85 

 80 



60 



250___ __ 



70 



250 



80 







According to the yield tables, an acre of normal loblolly pine, 

 site index 110, will "yield at 60 years of age 63,000 board feet, 

 international rule. As this particular tract is only 90 per cent 

 normal the standard yield must be reduced by 10 per cent, 

 which brings it down to 56,700 feet. Similarly the yield for the 



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