PART III 

 THE GROWTH OF TIMBER 



CHAPTER XXn 

 PRINCIPLES UNDERLYING THE STUDY OF GROWTH 



244. Purpose and Character of Growth Studies. The growth of 

 timber is studied in order to determine the rate of annual production 

 of wood as a crop on forest land. The yield of farm products is annual 

 and is measured at harvest. The essential difference between farm 

 and wood crops is that the period required to produce the latter is many- 

 years in extent, and due to this fact forest land is not the only capital 

 involved in crop production. The growth which the trees lay on 

 annually becomes in turn part of the capital to which future growth 

 is added in the same manner as interest which is added to a savings 

 account. 



This increase in total volume of a stand of timber does not continue 

 indefinitely, but only up to a certain age, which marks the culmination 

 of growth of the stand, from which time the losses occurring in the stand 

 more than counterbalance growth, and its volume and value diminish. 

 Forest crops therefore mature as do annual crops and one of the pur- 

 poses of growth study is to determine the period required for maturity. 



The basic facts to be determined in the study of growth are, first, 

 the total yield of stands in terms of quantity of products, quality, and 

 money value, for the period requued to grow a crop of timber from 

 origin to maturity; second, the average annual rate of growth to which 

 this final yield is equivalent, which is termed the mean annual growth 

 and is comparable to sunple interest on land as capital or to annual 

 crops; thud, the actual growth or increase in volume, quality, or value, 

 laid on during definite periods in the growth of the stand. The growth 

 for these short periods is expressed either as current annual growth which 

 is the growth for a single year, periodic annual growth which is the aver- 

 age annual growth for a short period, or periodic growth which is the 



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