Effect of 

 criteria used 

 on productive 

 capacity 



The timber harvest that can be sustained 

 from any forest area depends upon three 

 factors : 



• The amount of forest area that is suita- 

 ble and available for timber production 



• The productive capacity of this land 



• The intensity of timber management 



In the short run, of course, the cutting level 

 also depends upon the amount of merchantable 

 volume immediately available. 



Comparison of timber volume estimates of 

 an earlier and a current inventory is for the 

 most part risky because of the impact of cut- 

 ting in the interim period. Also, during the in- 

 terim betvi^een the two inventories for any unit, 

 improvements have been introduced in volume 

 estimating techniques. Two separate compila- 

 tions were made for the Coconino Forest using 

 the 1969 data; this enabled us to avoid the 

 above problems and more reahstically compare 

 impact of the factors studied on the timber 

 base area with impact on volume and growth 

 capacity. The first estimate of timber base area, 

 volume, and growth was based on the subjec- 

 tive field classification of inventory volume 



samples; this is the way inventory classification 

 has been handled in the past. The second com- 

 pilation was made by using study criteria. 



It is significant that the reductions in the 

 timber volume were about the same as the re- 

 duction in growing base area, but the impact on 

 growth capacity was much less. The following 

 tabulation shows these reductions: 



Percent 



Timber growing base area 28 

 Timber volume 29 

 Growth capacity 18 



The fact that there was a greater reduction 

 in volume than in growth capacity suggests 

 there has been proportionately more logging on 

 the more productive land. Further analysis of 

 growth capacity leads to the conclusion that 

 following logging the better sites have regener- 

 ated more rapidly. 



The real effect is less. — The 22 percent re- 

 duction in the estimate of timber growing base 

 for the six National Forests does not represent 

 an actual 22 percent loss of area and produc- 

 tivity for timber growing. It is true that the 

 awakening interest in forest values other than 



20 



