insect susceptibility and low growth rate, are 

 harvested at each cut. If the same total volume 

 is thus removed in lighter cuts per acre, more acres 

 will be cut over annually and conversion of virgin 

 forest to net-growth condition may be accomplished 

 in a relatively short cutting cycle. 



Current gross growth provides a measure of the 

 maximum effective increment during the first 

 cycle following application of this method of cut- 

 ting. The portion of this maximum that will 

 actually be achieved is, of course, unknown, but 

 there is a realistic opportunity of speeding the 

 recovery of a substantial part of total gross growth 

 by such alteration of cutting practice. 



Immature Stands 



Stands not more than 160 years old cover 26 

 percent of the region's area of commercial forests, 

 consisting of young forests that have followed clear 

 cutting or burning and residual stands left in con- 

 dition of net growth by selective cutting. Their 

 current annual gross growth totals 158 million 

 cubic feet or 252 million board feet. After allow- 

 ing for the low normal mortality characteristic of 

 these thrifty stands, net annual increase in volume 

 is 138 million cubic feet or 219 million board feet. 



Location, species, and quality influence the 

 economic availability of this increment. Approxi- 

 mately one-half is in ponderosa pine types (table 

 22) and there is little doubt of its potential avail- 

 ability, not only because ponderosa pine is com- 

 mercially desirable but also because these stands 



Table 22. — Annual increment in stands of the ponderosa pine types in 

 terms of total saw-timber growth in all stands, by survey units, 7936 



State and unit 



Gross growth 



Net growth 



Eastern Washington: 



Chelan-Colville 



Percent 



39 

 37 

 35 



Percent 



33 





40 





25 









38 



35 







Eastern Oregon: 



43 



70 

 75 



77 



37 





77 





75 





19 









69 



59 









58 



48 







are as a whole favorably located. Of the other 

 half of the net growth, probably a large part will also 

 be economically loggable at a time and in amounts 

 dependent upon market values and production 

 costs. Quality of net growth in both type groups 

 is far lower than that of timber now being logged. 

 It is estimated that only one-fifth of the total net 

 growth is being put on trees 22 inches d. b. h. or 

 more. In contrast, more than four-fifths of current 

 timber drain is in trees of this size class. 



All Commercial Stands 



If no reduction is made for losses by mortality and 

 decay, the total gross growth in the region is 341 

 million cubic feet or 1,145 million board feet an- 

 nually. This growth in cubic feet amounts to 1.1 

 percent of the region's total timber stand; in board 

 feet, to 0.9 percent. Two-thirds of it is in ponderosa 

 pine types but only 58 percent on ponderosa pine 

 trees, largely because the volume of other species in 

 the pine types is greater than the ponderosa pine 

 volume in the nonpine types (table 22). In con- 

 trast ponderosa pine suffers 87 percent of the total 

 cutting depletion. 



Total regional net growth is identical with that 

 occurring in the immature stands. Net increment 

 in cubic measure is 40 percent, that in board 

 measure is only 1 9 percent of total gross growth, the 

 remainder being at present offset by mortality. 



Periodic Growth 



In this region, where extensive virgin forests are 

 being rapidly cut over, the change in growth rate is 

 so rapid that the trend of growth is of far greater 

 significance than is its current level. As here com- 

 puted, periodic growth is the net increment that 

 will occur concurrent with probable cutting, fire, 

 and mortality depletion 6 during three decades 

 under three classes of cutting practice in ponderosa 

 pine stands: (1) Light selection cutting (the most 

 mature, least thrifty 50 percent of the virgin stand 

 per acre) on lands of all ownerships; (2) heavy 

 selection cutting (75 percent removal per acre) on 

 private lands and light selection cutting (50 per- 



6 Allowance was made for insect, windfall, and disease 

 mortality in immature stands at estimated normal rates. 

 Allowance was made for these factors in virgin stands by 

 assuming that, on the whole, growth balances mortality 

 therein. 



402110° 



45 



