66 



TIMBER RESOURCES FOR AMERICAS FUTURE 



Disease Causes the Greatest Growth 

 Impact 



Diseases far outrank all other causative agents 

 in their total adverse effects on forest productivity. 

 Although diseases do not kill as much timber out- 

 right as do insects or weather, their total growth 

 impact is far greater. In terms of either saw- 

 timber or growing stock, diseases account for 45 

 percent of the growth impact caused by all de- 

 structive agents (table 39). 



Sectionally, disease occasions the greatest grow- 

 ing stock mortality in the North, and the greatest 

 sawtimber mortality in the West. The South 

 ranks relatively low compared to other sections in 

 extent of disease mortality (table 41). 



One reason why diseases rank higher than other 

 destructive agents in terms of growth impact and 

 lower than insects in terms of mortality is because 

 many diseases such as the heart rot, leaf diseases, 

 and the killers of seedlings and saplings cause little 

 mortality of growing stock, yet account for a large 

 share of the ultimate effect of disease on production 

 of wood. Most of the forest tree diseases are 

 native, but occasionally these normally endemic 

 diseases become epidemic. Some of the most de- 

 structive diseases, for example, the white pine 

 blister rust and the chestnut blight, are not 

 native, but have been introduced from other con- 

 tinents. 



Heart rot and other stem diseases cause 27 per- 

 cent of disease mortality, and over 80 percent of 

 the growth impact due to diseases (table 42). 

 Other important groups in terms of mortality 

 caused by disease are the systemic diseases which 

 include birch dieback, pole blight of western white 

 pine, oak wilt, and sweetgum blight, and the root 

 diseases including Douglas-fir root rot and little- 

 leaf disease of shortleaf pine. 



Fire Is Potentially the Greatest Enemy 



The effects of fire, as is true with other agents, 

 vary from year to year. Growth impact from fire 

 in 1952 was about 8 percent less than the average 

 for the previous 5-year period. In 1952, fire ac- 

 counted for 6 percent of the total sawtimber mor- 

 tality, and 7 percent of the growing stock mor- 

 tality. In terms of growth impact, fire was rela- 

 tively more important and accounted for about 15 

 percent of the total damage caused b}^ all destruc- 

 tive agents. 



Moreover, fires often set the stage for subsequent 

 attacks by insects and diseases. They often de- 

 stroy wildlife and forage for domestic livestock 

 and big game. Likewise, fires occasionally result 

 in loss of human life, and severe fires are often 

 followed by floods and accelerated erosion. Fire 

 can eliminate the forest completely and remove 

 land from timber production for many years. 



Mortality from fire was most serious in the West 

 in terms of sawtimber, and in the South in terms 

 of growing stock. Fire causes a larger share of 

 total mortality in the South than in either the 

 North or West (table 41). 



Fire was the first of the serious destructive 

 agents which was aggressively attacked through 

 the organized and cooperative efforts of Federal, 

 State, and local governments and owners of pri- 

 vate forest land. Great progress has been made 

 as shown by such criteria as the area protected in 

 relation to the total area needing protection, the 

 class of protection applicable to different areas, 

 and the area burned each year. 



An estimated 673 million acres in the United 

 States needs protection from fire. This includes 

 nearly all commercial forest land and approxi- 

 mately 185 million acres of noncommercial forest 

 land.'^ Noncommercial forest land needs protec- 

 tion because it is intermingled with or adjacent to 

 commercial timberland or is highly valuable 

 watershed or recreation land. Eighty-eight per- 

 cent, or 591 million acres, of the total needing 

 protection now receives it in some degree in 1952 " 

 (fig. 31). Nearly 100 percent of Federal owner- 

 ships receive some degree of protection, 93 percent 

 of other public ownerships, and 81 percent of the 

 private forest land (table 43) . 



591 million acres 



82 million acres 



includes Coastal Alaska 



Figure 31 



'3 A relatively small acreage of 10 million acres of non- 

 forest land in California and North Dakoia is included in 

 these estimates and cannot be readily segregated. 



'* The unprotected area which needs protection dropped 

 from 82 million acres in 1952 to 41 million acres in 1957. 



