442 



CURRENT OR PERIODIC GROWTH OF STANDS 



the minimum expectancy and is safe for a long future period (§ 248). 

 Studies of growth on the individual trees and on permanent sample 

 plots as stimulated by release will in time indicate the maximum growth 

 possible on the same area. The actual growth will be somewhere 

 between these two extremes, dependent on the balance between the 



forces tending to expand the crown 

 area, and the destructive agencies 

 tending to reduce the numbers in the 

 stand, as shown in Fig. 87 by the lines; 



A. Based on average growth per 

 acre in original stand, with normal 

 )oss of numbers. 



B. Based on increased growth after 

 cutting and no loss of numbers. 



C. Probable rate somewhere between 

 A and B, based on increased growth 

 of a part of the stand and a reduced 

 rate of loss in numbers. 



Probably the safest basis for growth 

 prediction for long periods on cut- 

 over lands is not the current growth 

 study based on diameters, but, where 

 possible, yields based on age, at the 

 rate produced in the past on virgin 

 forests, and figured for the net areas 

 stocked, to which a percentage of in- 

 crease may be added to represent expansion of crowns due to release 

 and stimulus following cutting. 



An illustration of tliis principle of growth prediction is as follows : 



The empirical yield table for Western yellow pine, Coconino National Forest, 

 Arizona, gives 66.2 per cent of the normal or index yield. 



The stand of timber left on the cut-over areas, separated into three age classes 

 by the method given in § 321 is found. 



By dividing the stand for each age class by the yield per acre from the empirical 

 yield table, the area which is stocked with timber, for each age class, is determined. 



The area reproduced to poles and saplings is estimated. The total area of cut- 

 over land is known. The remaining area, not shown as stocked either with mature 

 timber or young timber is the area cut clean and awaiting restocking. The results 

 are given in Table LXVII. 



The prediction of growth is now made by applying the empirical 

 yield table to the areas and ages represented in the table. 



With the area and age of each age class indicated, the future yields 

 on cut-over lands may be predicted by applying the empirical yield 

 table, increased by the per cent of expansion agreed upon. 



Fig. 



87. — Possibilities of Growth 

 on Cut-over Areas. 



