CHAPTER XXVIII 

 NORMAL YIELD TABLES FOR EVEN-AGED STANDS 



303. Definition and Purposes of Yield Tables. A yield table is 

 intended to show the yields per acre which can be expected from stands 

 of timber at given ages or for given periods, in terms of a given unit 

 of volume or of product. 



A complete yield table will show yields for successive decades 

 or five-year periods covering the range of age of a species. Ordinarily, 

 yield tables do not show the loss in yields per acre during the decadent 

 period in over-mature stands, but they can be constructed so as to do 

 so. In forests under management, the maximum ages shown are those 

 of the oldest stands before cutting. 



Yield tables are used primarily to predict the yield of existing 

 stands, hence they are assumed to represent the actual development 

 of individual or typical stands throughout their life cycle. This they 

 do not always do, since naturally stocked areas tend constantly to pass 

 from a condition of under-stocking to one of over-stocking. It follows 

 that the most reliable yield tables are those constructed for stands 

 grown under management, where thinnings have controlled the incre- 

 ment. 



Yield tables are the fundamental data required for the determination 

 of the value of forest lands and the profits of forestry, the appraisal 

 of damages to forest property, the choice of a rotation or average age 

 at which timber should be cut, the advisability of thinnings, the choice 

 of species, and the relative profit from expenditures for all forestry 

 operations on different sites. An accurate or even an approximate 

 knowledge of yields per acre and the average rate of growth per year 

 tends to place forestry on a business basis rather than one of blind 

 speculation. 



304. Standards for Yield Tables. Yield tables undertake to set 

 standards in which the variables affecting yield are eliminated. The 

 basis of all yield tables is a separation into site qualities, with separate 

 average yields for each quality, since the fundamental variable is site 

 quality. 



Form of stand requires separate yield tables for even-aged stands, 

 and many-aged stands (§ 252). 



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