timber has placed additional constraints on 

 timber growing opportunities. However, the 

 large reductions reported here are mainly re- 

 ductions in estimates rather than reductions in 

 fact. For example, thousands of acres of very 

 steep and unstable lands and areas not capable 

 of producing 20 cubic feet of wood annually 

 should never have been called suitable and 

 available for timber growing in the first place. 

 The reduced estimates of timber growing base 

 suggested by the findings of this study, there- 

 fore, Eire not so much because of recent en- 

 croachments of other uses on the timber grow- 

 ing base as they are a matter of more realistic 

 estimation of this base. 



In recent years there has been growing rec- 

 ognition that important factors affecting suita- 



bility and availability of forest land for timber 

 use have been overlooked in timber inventory 

 planning. In many cases, managers of National 

 Forests have made judgment adjustments of 

 timber inventory estimates to correct for fac- 

 tors not considered in timber inventories. As 

 indicated in table 3, although the estimate of 

 the timber growing base for the six National 

 Forests studied was 4.1 million acres, the cut- 

 ting levels established following completion of 

 the inventories for these Forests were based on 

 3.5 million acres being used for timber produc- 

 tion. In some cases, subsequent reevaluations 

 have resulted in further changes in the timber 

 growing base for purposes of calculating the 

 allowable cut. 



Table 3. — Area of the timber growing base: from previous inventory; area used in 

 management planning from previous inventory; and, area from study 

 inventory by unit 



Area of timber growing base 



Study 



yj^j^. Previous Management Study 



inventory plan inventory 



Thousand acres 



Lolo, R-1 745.2 745.3 629.1 



Arapaho, R-2 668.4 446.0 399.6 



Coconino, R-3 793.5 599.9 568.6 



Boise, R-4 385.3 368.7 273.3 



E. Klamath, R-5 420.1 420.1 372.3 



Gifford Pinchot, R-6 , 1,041.2 960.5 921.6 



Total 4,053.7 3,540.5 3,164.5 



21 



