18 



[THE OUTLOOK FOR TIMBER IN THE UNITED STATES' 



Potential and current net growth per acre 



POTENTIAL CURRENT 



north 

 south 

 rocky mountain 



pacific coast 



50 75 100 



CUBIC FEET PER YEAR 



Figure 7 



IMPACTS OF DESTRUCTIVE AGENTS 



Fire, insects, disease, storms, and other destruc- 

 tive natural agents have significant impacts on 

 net annual growth. Such impacts are partially 

 accounted for by the statistics on mortality (that 

 is, volumes of growing stock trees above 5.0 inches 

 in diameter dying from natural causes during a 

 given period). 



Volume of Mortality 



Annual mortality losses from natural causes 

 were estimated at about 4.5 billion cubic feet of 



growing stock in 1970. Mortality of sawtimber 

 amounted to an estimated 15.3 billion board feet 

 (that is, roughly 2.6 billion cubic feet in the saw-log 

 portion of sawtimber trees) (table 11). Mortality 

 thus nullified about one-fifth of the total annual 

 growth of both growing stock and sawtimber. 



Softwood species accounted for the major part 

 of mortality losses — that is, about three-fifths of 

 growing stock mortality and three-quarters of 

 sawtimber mortality. 



Most softwood mortality in 1970 was in the 

 West, chiefly in the Pacific Coast section (fig. 8). 

 This distribution is related to the concentration of 



Timber mortality by section, 1970 



GROWING STOCK 



SAWTIMBER 



total 



total 



south 



south 



28% 

 rocky mtn. 



north 



14% 



north 



rocky mtn. 



pacific coast 



pacific coast 



! I softwoods I 1 hardwoods 



Figure 8 



Table 11. — Mortality of growing stock and sawtimber on commercial timberland, by section and by softwoods 



and hardwoods, 1952, 1962, and 1970 l 



GROWING STOCK— BILLION CUBIC FEET 



Section 



All species 



Softwoods 



Hardwoods 





1952 



1962 



1970 



1952 



1962 



1970 



1952 



1962 



1970 



North 



South 



Rocky Mountains _ . 



0. 8 



1.0 



.6 



1.6 



1.0 



1. 1 



.6 



1.5 



1.3 



1. 2 



. 6 



1. 5 



0.2 

 .3 

 .6 



1.5 



0. 3 

 .4 

 .6 



1.4 



0.4 

 .5 

 .6 



1.4 



0.6 

 . 6 



( 2 ) 

 . 1 



0. 7 



. 7 



( 2 ) 

 . 1 



0.9 



.7 

 ( 2 ) 



Pacific Coast _ _ ___ 



. 1 







Total.. ___. --. 



3.9 



4.3 



4.5 



2.6 



2. 7 



2. 8 



1. 3 



1.5 



1.7 







SAWTIMBER— BILLION BOARD FEET 



North ... 



South 



Rocky Mountains _ 



1.5 

 2.6 

 2.5 



8.4 



1.9 

 3.0 

 2.6 



7. 8 



2.3 

 3. 2 

 2.6 

 7. 1 



0.4 



.9 



2.5 



8. 2 



0.5 



1. 1 



2. 5 

 7.6 



0. 7 

 1.3 

 2.5 

 6.9 



1. 1 



1. 7 



. 1 



. 2 



1.4 



2.0 



. 1 



. 2 



1.7 



1.9 



. 1 



Pacific Coast 



.3 







Total 



15. 1 



15.3 



15.3 



11.9 



11.6 



11.3 



3. 1 



3.6 



4.0 



1 Data may not add to totals because of truncating 



2 Less than 0.1 billion. 



Note: Data for 1952 and 1962 differ from data published 

 in earlier reports because of adjustments based on newer 

 information from remeasured Forest Survey plots. Data 

 for all years are "trend level" estimates. 



