220 A NATIONAL PLAN FOK AMERICAN FORESTRY 



Against the various causes of these losses science is waging relent- 

 less warfare. Forest entomologists have made notable progress in 

 devising methods for checking forest insect depredations, and in 

 working out control measures. Similarly, forest pathologists have 

 made notable progres,s against the inroads of disease. These two 

 phases of the forest problem, as well as that of forest-fire prevention 

 and control, are discussed in sections, "Progress in Forest Pathology " 

 and " Progress in Forest Entomology", under " Progress in Forestry 

 and Existing Plans"; also in sections, " Protection Against Fire", 

 "Protection Against Forest Insects", and "How to Stop Forest 

 Devastation", under "National Programs Required and the Respon- 

 sibility for Them." 



TIMBER GROWTH 



Growth is the characteristic which renders a forest, unlike a mine, 

 susceptible to use and replacement on a permanently productive basis. 

 Continued removal of timber without regard to or in excess of re- 

 placement by growth must sooner or later bring about the deteriora- 

 tion of the forest far below its producing capacity, if not its complete 

 destruction. Such treatment of forests has been aptly described as 

 timber mining. In an analysis of forest resources, therefore, a funda- 

 mental consideration is that of present and potential growth and of 

 the relation between growth, drain through cutting and through 

 losses by fire and other causes, and timber requirements. (See pre- 

 ceding subsection, "Forest Drain", and following section, "Our 

 National Timber Requirements"). 



CURRENT ANNUAL GROWTH 



The best available data on growth though employed, as in the 

 present discussion, with due consideration of age classes, density of 

 stocking, mixture of species, site differences, and other factors that 

 affect the rate of growth afford a basis only for rough estimates of 

 growth rates for the various forest types. Nevertheless, it is be- 

 lieved that the estimates and relationships presented and the infer- 

 ences drawn therefrom are in the main dependable. 



Table 17 gives the estimated present current annual growth in the 

 United States as a whole of material large enough for saw timber, as 

 well as that of all timber of usable size including both saw timber and 

 cordwood. The estimates are for net growth, after allowing for so- 

 called "normal " losses from decay, insects, etc. Abnormal or unusual 

 losses from disease or insect epidemics, fires, hurricanes, etc., are taken 

 care of in the estimates of drain. The growth in board feet consists 

 of the growth on the present saw-timber stands, after deducting the 

 growth on the saw-timber cut during the year and adding the total 

 saw-timber volume on that portion of the cordwood area which passes 

 into the saw-timber class each year. In the same way, the total 

 growth on cordwood and saw-timber areas combined, expressed in 

 cubic feet, consists of the net growth on stands remaining after the 

 year's cut, plus the total volume on the restocking areas which pass 

 into the cordwood class annually. 



