62 Forest Mensuration 



PARAGRAPH XCIV. 



NORMAL YIELD TABLES, THEIR PURPOSES AND CONTENTS ABROAD. 



Normal yield tables are especially used for the following purposes : 



1. To ascertain the quality of the soil (e. g., for taxation). 



2. To ascertain the volume of the growing stock. 



3. To ascertain future yields of the forest. 



4. To solve problems of forest finance, especially those of forest ma- 

 turity (length of rotation). 



German normal yield tables have the following contents : 



A. Tables for the main forest the secondary forest comprising such 



trees on the same lot as are about to be removed by way of thin- 

 ning: 



(1) Age, graded at five year intervals. 



(2) Number of trees. 



(3) Sectional area at chest height, inclusive of bark. 



(4) Average diameter. 



(5) Average height and height increment. 



(6) Volume in cubic measure arranged according to assortments 



as logs, fuel, bark, etc. 



(7) Periodical and average annual volume increment. 



(8) Increment percentage. 



(9) Form factor. 



(10) Normal growing stock. 



B. Tables for the secondary forest, giving merely its volume, which, 

 as stated, is to be removed by way of thinning. 



Circular 445 of the Bureau of Forestry defines "future yield tables" as 

 follows : "A tabular statement of the amount of wood which, after a 

 given period, will be contained in given trees upon a given area expressed 

 in board feet or some other unit." 



PARAGRAPH XCV. 



RETROSPECTIVE YIELD TABLES. 



In "retrospective" yield tables an attempt is made to rebuild the grow- 

 ing stock as it was before lumbering from the stumps found on the 

 ground and from stem analyses of the trees now standing. Prerequisite 

 is a knowledge of the year in which lumbering took place and of the 

 conditions of growth since prevailing. 



Method of proceeding : 



I. Make stem analyses and construct tree volume tables, showing the 

 probable contents of trees for stumps of a given diameter and for given 

 diameters b. h. 



