YIELD TABLES FOR STANDS GROWN UNDER MANAGEMENT 427 



In applying such a table, it can be assumed that the mortalit^^ in 

 the forest will be at the proportional rate indicated by the table. The 

 prediction of yields will then be based on a stand table giving the number 

 of trees in each diameter class. Several methods of applying the 

 standard table are possible, as 



1. Base the prediction upon the total number of trees in each diam- 

 eter class or group. The per cent of reduction in numbers is obtained 

 from the table. This per cent is applied to the stand in the forest, 

 and the future growth obtained by computing the future volume of 

 the remaining trees, as shown in the illustration. 



2, Base the prediction upon yields. The number of trees in each 

 diameter class is divided by the number per acre in the standard table. 

 This gives the area normally stocked by that class, from which its future 

 yield is taken directly from the standard yield table. This area forms, 

 of course, but a small per cent of the forest, and is the total area occupied 

 by trees of the diameter class. 



The forest can be divided into age classes, based on diameter, and 

 the area occupied by each of these age classes obtained as described 

 in § 316. 



At best, it can be seen that this substitution of standard yields 

 based on growing space per tree is a makeshift compared with determin- 

 ing these relations from even-aged plots in which the factors of site, 

 tolerance and soil at different ages are directly measured. 



326. Yield Tables for Stands Grown under Management. European 

 experience with stands grown under management has shown, first, 

 that the best results and heaviest total yields per acre are obtained 

 by several thinnings at frequent intervals, in which not only the trees 

 which would otherwise die before the next cutting are removed, but the 

 remaining crowns are freed from competition. 



Second, that the proportion of the total yield removed as thinnings 

 under this system may equal one-third or more of the total yield. 



Third, that the diameter growth of the surviving trees can by proper 

 thinnings be sustained at a uniform rate until the final crop is cut. 

 The development of each tree in the stand proceeds actually at the rate 

 of growth of a dominant tree which maintains its crown spread through- 

 out its life. 



Even where second-growth stands have sprung up, in this country, 

 and reached sizes suitable for logging, they have usually received no 

 care in the form of thinnings. Stagnation sets in on many of these 

 stands, especially with conifers on old fields, and the diameter 

 growth of the whole stand suffers. This occurs even in plantations 

 on which thinnings have been neglected. 



The actual yields and sizes which may be grown on such stands 



