396 NORMAL YIELD TABLES FOR EVEN-AGED STANDS 



The factor of density of stocking (§ 273) separates yield tables into 

 Normal or Index tables which are based on an average full or maximum 

 stocking, and Empirical tables, which represent the actual average 

 density of stocking on a given area including partially stocked and 

 unstocked portions. 



Composition of the forest is distinguished by constructing tables 

 for pure stands (§ 314) separately from mixed stands. 



The most important distinction is probably that made between 

 natural stands and those grown under management. Owing to the 

 great influence of treatment upon growth and yields, the standard 

 of normality (see above) is entirely different for natural and for arti- 

 ficially grown stands, and yield tables based on the yields of planted, 

 thinned and managed forests must be made to replace the present 

 normal yield tables, when the material for such measuremients becomes 

 available in sufficient quantity to furnish a proper basis. 



Normal or index yield tables serve their chief purpose as a standard 

 of comparison, since most stands will produce either larger or smaller 

 yields than those shown (§ 250). This function is better served if 

 the standard of normality set by the table is not abnormally high, 

 but is made to conform to the results possible of attainment on the 

 average acre of the site class, with reasonably thorough protection from 

 destructive agencies and reasonably full stocking. 



305. Construction of Yield Tables, Baur's Method. There are two 

 methods possible in the preparation of yield tables. The first, known 

 as Baur's method ^ is based on the measurement of the present volume 

 and age of numerous plots which are then classified as to site and age 

 and form the basis of curves of average yields based on age for from 

 three to four site classes. This method corresponds with the defini- 

 tion of a yield table cited in § 249 since it does not pretend to trace 

 the past history of these individual stands; yet the use to which such 

 a table is put is to predict from these average curves the growth of a 

 given stand by decades. For original stands under natural conditions, 

 this method is universally used. The second method is to re-measure 

 established plots at stated intervals to determine the volume of growth, 

 diminution in number of trees per acre and other changes in the stand. 

 While more accurate, the collection of such data must await the growth 

 of the timber and the method is best applied to stands under manage- 

 ment. 



Yield tables can be constructed by Baur's method on the basis of 

 from 50 to 200 plots dependent on the range of site qualities and condi- 

 tions of growth. The aim is usually to get at least 100 plots. 



1 Die Holzmesskunde, Franz Baur, Professor of Forestry, University of Munich, 

 Bavaria, 1891. 



