14- 





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12- 





1 1 ■ 





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9 





t— „ 

 z 8 





LU 



a 7- 









S 6- 





5- 





4- 





3- 





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13.6 



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 _c 



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 o 

 o 

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 c 



Figure 5. — Reductions in the timber base be- 

 cause of land instability. (Amounts shown 

 for Lolo and Coconino include other soil 

 factors, see table 2.) 



ment is the principal problem, but it is 

 not extensive. On the Boise, the un- 

 stable category is made up primarily of 

 granitic soils highly susceptible to both 

 surface erosion and mass slumps. 

 Land instability is a localized problem. On 

 some National Forests it is not an important 

 factor. In others, like the Boise, it is the most 

 crucial single consideration in land 

 classification. 



SMALL ISOLATED PATCHES 



Throughout the Western United States, for- 

 est land capable of producing timber crops 

 commercially is located within a broad or nar- 

 row elevational range that varies by latitude 

 and rainfall patterns. At lower extremes it gen- 

 erally fades into noncommercial timber, brush, 

 and grass. At the upper elevations, subalpine 

 timber and shrubs take over. In both the lower 

 and upper transition zones those trees that are 

 of commercial quality often occur in small scat- 

 tered patches where, for one reason or another, 



there is greater moisture or deeper soil (fig. 6). 



In most of the previous timber inventories, 

 forest land area was estimated from point sam- 

 ples on aerial photographs. Even very isolated 

 patches of timber land as small as 1 acre in size 

 were considered to be timber growing land if 

 they met the other requirements. Experience 

 has shown this to be a faulty procedure because 

 on many such areas the costs of, and damages 

 from, utilization are more than the trees are 

 worth. 



In our analysis, no area smaller than 10 acres 

 was considered usable for timber growing. 

 Areas of productive forest land from 10 to 40 

 acres were considered usable only where they 

 were close to larger bodies of forest land and 

 could be utilized along with the main forest or 

 were otherwise highly accessible. In all cases, 

 the criteria of size and accessibility for these 10 

 to 40 acre areas were developed locally by Na- 

 tional Forest and Regional personnel (fig. 7). 



Table 2 indicates that the small isolated 

 patches of timber excluded on two Forests 

 (Lolo and Gifford Pinchot) did not account for 

 much acreage. On the East Klamath Working 

 Circle and on the Boise National Forest, how- 

 ever, large acreages were excluded due to size 



Figure 6. — Reductions in the timber base be- 

 cause of isolated stringers or small patches. 



17 



