sions drawn from this simple comparison are 

 likely to be misleading unless they are modified 

 by analysis of existing growing stock and prevail- 

 ing forest practices. 



Sites occupied by commercial forest stands total 

 15,771,000 acres, of which 11,654,000 acres bear 

 mature stands, i. e., more than 160 years old, and 

 4,117,000 acres immature. 



Mature Stands 



On the 74 percent of the region's commercial- 

 forest area that is in mature timber, a gross annual 

 growth is being achieved that in 1936 was 183 

 million cubic feet or 893 million board feet (table 

 21). But in spite of this, mature timber as a class 

 suffered a loss in volume from 1917 to 1936, owing 

 principally to insect epidemic and severe drought. 

 For the next several decades, however, a net in- 

 crement may be anticipated in such stands owing 

 to the release that losses from insect attack have 

 afforded the remaining trees and to the greater 

 rainfall following the earlier abnormal drought. 

 Although some stands have continued to lose 

 volume despite such release, it is believed that for 

 larger areas such periods of loss are followed by 

 periods of gain. It is impossible as yet, however, 

 to predict mortality of unmanaged mature stands 

 with more detail than is involved in the general 

 assumption that it will in the long run equal gross 

 growth over large areas. 



Thus it is that three-quarters and more of the 

 total gross saw-timber growth in the region is at 

 present being nullified by mortality caused prin- 

 cipally by insects. Unlike that in many forest regions, 

 this mortality is chiefly in high-quality trees. Rec- 

 ords of the Bureau of Entomology and Plant Quaran- 

 tine show that the average ponderosa pine tree killed 

 by insects is about 32 inches in diameter and that 90 

 percent of the loss is in trees 22 inches in diameter, or 

 more. Reduction of this wide discrepancy between 

 gross and net growth is one of the region's most 

 urgent forest-management problems. 



Forest managers believe that by substituting light, 

 thrifty-maturity selection cutting at frequent inter- 

 vals for clear cutting or heavy selection, the mor- 

 tality now occurring in the virgin stands can be 

 reduced much more rapidly. Under this system 

 only the least thrifty, most mature trees, of high 



Table 21. — Current annual growth 1 ponderosa pine regio 

 MATURE STANDS 2 



1936 



State and unit 



Area 



Cubic-foot 

 growth 



Board-foot 

 growth 





Gross 



Net 



Gross 



Net 



Eastern Washington: 

 Chelan-Colville- . 



Thou- 

 sand 

 acres 

 2,285 

 1,422 

 124 



Million 



cubic 



feet 



34 



29 



2 



Million 

 cubic 

 feet 



Million 



board 



feet 



154 



144 



7 



Million 

 board 

 feet 



Yakima River. 





North Blue Mountain . . 





Total 



3,831 



65 





305 









Eastern Oregon: 



North Blue Mountain __ 

 Deschutes River. . . . 

 South Blue Mountain _ _ 

 Klamath Plateau ._ 



1,387 

 1,582 

 2,428 

 2,426 



21 

 27 

 29 

 41 





89 

 144 

 136 

 219 





Total 



7,823 



118 





588 





Region total __ _ 



11,654 



183 





893 





IMMATURE 



STANDS 3 







Eastern Washington: 



Chelan-Colville 



1,103 

 713 

 162 



37 

 30 



7 



32 



26 

 6 



74 

 58 

 8 



64 



Yakima River... .. 



50 



North Blue Mountain . . 



7 



Total.... 



1,978 



74 



64 



140 



121 



Eastern Oregon: 



North Blue Mountain . . 



Deschutes River j. 



South Blue Mountain... 

 Klamath Plateau _ _ 



799 

 401 

 457 

 482 



33 

 19 

 18 

 14 



29 

 16 

 16 

 13 



44 

 18 

 21 

 29 



39 

 16 

 18 



25 



Total 



2,139 



84 



74 



112 



98 





4,117 



158 



138 



252 



219 







ALL STANDS 



Eastern Washington: 

 Chelan-Colville 



3,388 

 2,135 



286 



71 

 59 



9 



32 



26 



6 



228 

 202 



15 



64 



Yakima River. . 



50 



North Blue Mountain _ . 



7 



Total 



5,809 



139 



64 



445 



121 







Eastern Oregon: 



North Blue Mountain . . 



Deschutes River 



South Blue Mountain. __ 

 Klamath Plateau.. 



2,186 

 1,983 



2,885 

 2,908 



54 

 46 

 47 

 55 



29 

 16 

 16 

 13 



133 

 162 



157 

 248 



39 

 16 

 18 

 25 



Total '_ 



9,962 



202 



74 



700 



98 



Region total . 



15, 771 



341 



138 



1,145 



219 



1 Cubic-foot growth is for that portion of the stem of trees 5.1 inches 

 d. b. h., or more, between stump and top 4 inches in diameter inside bark, 

 exclusive of bark and limbwood. Board-foot growth is for trees 11.1 

 inches, d. b. h., or more, in 16-foot logs to an 8-inch top, Scribner rule. 



2 Stands more than 160 years old, on commercial conifer forest land. 



3 Stands 160 years or less in age, on commercial conifer forest land. 



44 



