14 



iTHE OUTLOOK FOR TIMBER IN THE UNITED STATES 



Table 5. — Area of commercial timberland in the United States, by site productivity class and by section, 



1970 



Productivity class 

 (cubic feet per 

 acre per year) 



Total 

 United States 



North 



South 



Rocky Mountains 



Pacific Coast 



120 or more 



Million 

 acres 



52 

 116 

 195 

 131 



Percent 

 10.4 

 23.5 

 39.5 

 26. 6 



Million 

 acres 



10 

 39 

 69 

 60 



Percent 



5.5 



22. 1 



38. 8 



33.6 



Million 

 acres 



13 

 53 

 90 

 36 



Percent 



7.0 



27. 8 



46.5 



18. 7 



Million 

 acres 



5 



8 



14 



30 



Percent 



8.4 



13. 8 



24. 5 



53.3 



Million 

 acres 



24 



16 



23 



6 



Percent 

 34. 9 



85 to 120 



23.0 



50 to 85 ... . 



33.9 



20 to 50. _ . . . 



8. 2 









l 495 



100.0 



178 



100.0 



192 



100. 



57 



100.0 



68 



100.0 



1 Not including 5 million acres in National Forests in the Rocky Mountains classed as "unregulated" commercial 

 timberlands. 



potentials, and responses to cultural practices, on 

 the Nation's commercial timberlands. 



About 10 percent of all commercial timberlands 

 were classed as site 120 or more, that is, capable 

 of producing 120 cubic feet or more per acre per 

 year in fully stocked natural stands (table 5). 

 (Under intensive management more timber can 

 be produced than indicated by such figures for 

 natural stands.) Nearly half of this highly produc- 

 tive land is in the Pacific Coast section, largely 

 supporting Douglas-fir, hemlock-Sitka spruce, and 

 western hardwoods. Each of the other sections 

 also contain some of this high-site land. 



Nearly two-thirds of the total area of commercial 

 timberland is in the 85 to 120 and the 50 to 85 

 cubic foot site classes. About half of this acreage 

 is in the South. 



The remaining area of 20 to 50 cubic foot growth 

 potential makes up more than a quarter of all 

 commercial timberlands. This class of land provides 

 limited response to timber management activities 

 but often yields important values for grazing, 

 recreation, or other non timber uses. These lower- 

 site lands are mostly in eastern areas such as the 

 Appalachians, and in the Rocky Mountains where 

 this site class makes up about half of that section's 

 commercial timberland . 



A relatively large proportion of the better sites 

 above 85 cubic feet are in forest industry owner- 

 ships. The National Forests and other public 

 ownerships have relatively high proportions of 

 the poorer sites of less than 50 cubic feet potential. 



Timber Stocking 



The potential yields indicated by site produc- 

 tivity classifications are generally not realized, 

 even though practically all commercial timber- 

 lands in 1970 were occupied to some extent by 

 some type of tree cover, and many forests were 

 fully stocked or even overstocked in terms of all 

 live trees. 



Illustrative data for a number of sample hard- 

 wood forest areas indicated, however, that only a 



fifth of the land supported desirable trees of good 

 form, vigor, and preferred species. Growing stock 

 of acceptable trees, and trees classed as rough and 

 rotten, made up the lemaining tree stocking. An 

 estimated 90 percent of the land in these sample 

 areas would require cultural treatments such as 

 cull tree removal or thinnings to achieve a high 

 level of output of merchantable timber and thus 

 approach the yield potentials indicated by indexes 

 of site productivity. 



St and -Size Classes 



The distribution of forest areas by stand-size 

 classes largely reflects the recency of timber har- 

 vesting and other factors such as fires or reversion 

 of farm land to forest. Stand size is also indicative 

 of prospective supplies of industrial timber, and a 

 basic factor in the planning of timber management. 



About 44 percent of all commercial timberlands 

 supported sawtimber stands in 1970 (table 6). 

 Poletimber stands made up 26 percent, and seed- 

 ling and sapling stands 27 percent, with some 4 

 percent classed as nonstocked. 



Sawtimber stands made up a sizable part of the 

 total area in the South and in the North, even 

 though most forests in these sections have been 

 cutover one or more times. Most of these eastern 

 sawtimber stands are relatively young and com- 

 posed of trees in the lower part of the sawtimber- 

 size range. 



Much larger proportions of western forests 

 supported sawtimber stands, including consider- 

 able old-growth areas that have never been cut. 

 Stands on the Pacific Coast contain most of the 

 large-size, high-quality sawtimber remaining in 

 the United States. 



Wide differences in timber volumes per acre are 

 also illustrated by data in table 7. Nearly half of 

 all commercial timberlands supported less than 

 1,500 board feet per acre in 1970. Only 23 percent 

 had inventory volumes of more than 5,000 board 

 feet per acre. 



