PREDICTION BASED ON GROWTH OF TREES 437 



uncertainty are probable loss of numbers in the next period, and future 

 rate of diameter, height and volume growth of the survivors. At best, 

 owing to the great difficulty of predicting for a given stand the loss in 

 numbers and the rate at which diameter growth will be maintained, 

 for long future periods, the method can be used only for periods of 

 ten to twenty years, except for slow-growing or long-lived species where 

 the factors of change are slowed down correspondingly. 



To apply this method of predicting tree growth to obtain current 

 growth of stands, the steps are, 



1. Prepare a stand table of the forest or area (§ 188). 



2. As an aid in determining mortality, tally or estimate the number 

 or per cent of each diameter class which is suppressed or will probably 

 die within ten or twenty years. 



3. Decide upon the method to be applied in predicting diameter 

 growth (§ 278 and § 279) and prepare table of growth by diameter 

 classes to conform to the requirements of the method. 



4. Obtain data and construct a curve of average height growth 

 (§ 248), which will probably be best expressed as current height growth 

 based on height, for the last decade or two. 



5. Obtain volume tables giving the volume of trees of each diameter 

 and average height. A standard volume table classified by heights is 

 needed for best results. 



6. From present number of trees in each diameter class, deduct 

 the per cent or number which will probably die within the period. 



7. Compute the average diameter which surviving trees of each 

 diameter class will attain at end of period. 



8. Compute the increase in height for each diameter class. (The 

 false method described in § 285 is frequently used as a substitute for 

 a curve of height growth.) 



9. The volume of the present stand is calculated from the stand 

 table and volume table. 



10. The volume of the surviving stand at end of period is obtained 

 from the future diameter and height of the surviving trees of each diam- 

 eter class, and volumes taken from the standard volume table. 



11. The difference in volume thus found is the net growth for 

 the period, in stands which have not been thinned and in which no 

 salvage of dying or dead timber is possible. The volume- of the trees 

 which die is thus deducted from the growth on the survivors, and 

 only the net growth is represented in increased volume of the stand. 



In stands which are thinned, this prospective loss in numbers is 

 not lost nor deducted, but is expressed in the form of thinnings. Where 

 thinnings are marked and will be made in such stands, they will com- 

 monly include more trees than will actually die during the period, 



