21-i 



Terrestrial Eiosysteiiis — Our Living Resources 



This is shown by Henderson and Epstein (this sec- 

 tion) in their discussion of how fire supression and 

 other factors caused tremendous losses of oak 

 savannas throughout the Midwest, hi other sys- 

 tems, an increase in fire frequency can also lead to 

 changes in ecosystem structure and function. 

 Although we now realize that fire is a natural and 

 necessary part of many ecosystems, it was not 

 until after the devastating fires of Yellowstone 

 National Park that the general public was alerted 

 to the benefits of such fires (Elfring 1989). An 

 effective fire-suppression program can allow 

 accumulation of vast amounts of detritus (dead 

 organic material such as leaves, branches, and 

 stems). If this material is not consumed period- 

 ically by small fires burning along the forest 

 floor, it will accumulate to the point of provid- 

 ing raw materials for an exceptionally intense 

 fire that can bum tree crowns and destroy the 

 existing forest. FeiTy et al. (this section) discuss 

 four fire-adapted ecosystems that have been 

 affected by modified fire regimes and conclude, 

 "Managers must balance the suppression pro- 

 gram with a program of prescribed fire applied 

 on a landscape scale if we are to meet our stew- 

 ardship responsibilities." 



Numerous variables in addition to disease 

 and fire affect our natural resources. These vari- 

 ables include pollution (Peterson, this section; 

 Nash et al., this section), conversions to other 

 uses, harvesting activities such as logging, and 

 global climate change. Cole (this section) 

 demonstrates that over the past 5,000 years 

 change has been a natural part of our terrestrial 

 ecosystems. Within a given ecosystem some 



species decline in importance while others 

 increase over time, resulting in a change in the 

 overall character of the ecosystem. A key fea- 

 ture to stand out in the 5,000-year chronology 

 developed by Cole is that cunent rates of 

 change are about 10 times higher than presettle- 

 nient rates. Human intervention in one form or 

 another is now the principal agent of change. 

 Darr (this section) provides a review of U.S. 

 Forest Service data and discusses changes being 

 brought about by forestry-management prac- 

 tices. At a reduced spatial scale, Keeland et al. 

 (this section) discuss changes within the forest- 

 ed wetlands of the southeastern United States. 

 Forested wetlands have been especially reduced 

 and fragmented as a result of land-use conver- 

 sions, predominantly to agricultural activities. 



A common thread here, as in all sections in 

 this report, is that if unchecked, human activi- 

 ties will continue to result in an upset balance of 

 species interactions, alteration of ecosystems, 

 and extensive habitat loss. 



References 



Burgess. R.L.. and D.M. Sharpe. eds. 1981. Forest island 

 dynamics in man-dominated landscapes. Springer- Verlag, 

 New York. 310 pp. 



Elfring, C. 1989. Yellowstone: fire stomi over fire manage- 

 ment. BioScience 39(10):667-672, 



Harris. L.D. 1984. The fragmented forest. The University of 

 Chicago Press. Chicago. 211 pp. 



Shugart. H.H.. and D.C. West. 1977. Development of an 

 Appalachian deciduous forest succession model and its 

 application to assessment of the impact of the chestnut 

 bliaht. Journal of Environmental Management 5:161-179. 



U.S. Forest 

 Resources 



by 



David R. Darr 

 U.S. Forest Service 



450 



400 

 _350 

 I 300 

 1250 

 g200 



m 



1150 



^100 



50 







g fe 20 38 53 63 70 77 87 92 



CD en ,, 



^ ^ Year 

 Fig. 1. Forest land area (Powell et 

 al. 1993). 



The Secretary of Agriculture is directed by 

 law to make and keep cun'ent a comprehen- 

 sive inventory and analysis of the present and 

 prospective conditions of and requirements for 

 the renewable resources of U.S. forests and 

 rangelands. This inventory includes all forests 

 and rangelands, regardless of ownership. The 

 work is cairied out by people in the Forest 

 Inventory and Analysis program of the U.S, 

 Department of Agriculture Forest Service 

 (USFS). 



Inventories provide key forest lesource 

 information for planners and policy makers. 

 Increasingly, people turn to these inventories for 

 information on biological diversity, forest 

 health, and developmental decisions. 



Information is collected from over 130,000 

 permanent sample plots selected to assure sta- 

 tistical reliability. Vegetation on the plots is 

 measured on average about every 10 years. 

 Characteristics of the vegetation and land are 

 measured, including ownership, productivity 

 for timber production, the kinds and sizes of 

 trees, how fast trees are growing, whether any 



trees have died from natural causes, and 

 whether any trees have been cut (USFS 1992). 



Characteristics of Forest Land 



Over the years, the U.S. forest cover has 

 changed because of the way people use and 

 manage forest land. Today, about 33% of the 

 U.S. land area, or 298 million ha (737 million 

 acres), is forest land, about two-thirds of the 

 forested area in 1600 (Fig. 1 ). Since 1600. soine 

 1 24 million ha (307 million acres) of forest land 

 have been converted to other uses, mainly agri- 

 cultural. More than 75% of this conversion 

 occurred in the 19th century, but by 1920. clear- 

 ing forests for agriculture had largely halted. 



Some 34% of all forest land is federally 

 owned and managed by the U.S. Forest Service, 

 the Bureau of Land Management, and other fed- 

 eral agencies. The rest is owned by nonfederal 

 public agencies, forest industry, farmers, and 

 other private individuals. About 19 million ha 

 (47 million acres; 6% of all U.S. forest land) are 

 reserved from commercial timber harvest in 



