ACCRETION OF A FELLED TREE. 



143 



their respective cross-sectional areas at that point by the length 

 of the topless trunk. 



A more careful stem analysis of a tree affords detailed meas- 

 urements from which the volume at any time during its lifetime 

 may be determined very accurately. The following table of 

 measurements of a pine will furnish data for the calculation of 

 its volume at different ages, and its progressive development is 

 graphically illustrated in Figure 38: 



The Accretion of a Forest for a given number of years 

 is found by multiplying the accretion of the sample tree for that 

 period by the number of trees per acre and the number of acres 

 in the tract. If the trees are arranged in diameter classes, the 

 accretion of each class is determined, and the sum of accretions 

 of all the classes taken as the accretion of the forest. 



The Working Plan of a forest contemplates the economic 

 management of the growing crop, so that there may be cut each 

 year not to exceed the amount of the annual accretion; or, if 

 worked on the rotation plan, so that there may be cut at any one 

 time not more than the accretion for the period of rotation, thus 

 leaving the capital stock unimpaired. The methods of measure- 

 ment described are used in outlining this plan. 



The Estimation of Standing Timber is usually a matter 

 of personal experience on the part of the estimator. No meas- 

 urements are taken of trees, but the estimate is made by men of 

 long experience in the woods. Sometimes their figures are very 

 close, but more often they fall short of the actual stand of tim- 

 ber. Buying and selling timber lands is based on this method of 

 determining the possible crop, both parties sending out their 



