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U.S. Forest Resources


by
David R. Darr
U.S. Forest Service
The Secretary of Agriculture is directed by law to make and keep current a comprehensive 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 carried out by people in the Forest Inventory and Analysis program of the U.S. Department of Agriculture Forest Service (USFS).
Inventories provide key forest resource 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 statistical 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, some 124 million ha (307 million acres) of forest land have been converted to other uses, mainly agricultural. More than 75% of this conversion occurred in the 19th century, but by 1920, clearing forests for agriculture had largely halted.

Fig. 1. Forest land area (Powell et al. 1993).
Some 34% of all forest land is federally owned and managed by the U.S. Forest Service, the Bureau of Land Management, and other federal 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 wilderness, parks, and other land classifications.
Forest land is widely but unevenly distributed. North Dakota has the smallest percentage of forest cover (1%) and Maine has the greatest (89%). Forest areas vary greatly from sparse scrub forests of the arid interior West to the highly productive forests of the Pacific coast and the South, and from pure hardwood forests to multispecies mixtures and coniferous forests. In total, 52% of the forest land is east of the Great Plains states. In the East, the oak-hickory forest type group is most common, while in the West, the category referred to as "other softwoods" is most common.
U.S. forests provide wildlife habitat and thereby support biodiversity; take carbon out of the air and thus serve as carbon sinks; and provide the outdoor environments desired by many people for recreation.
Timberland forests are logged for lumber, plywood, and paper products. This timberland is generally the most productive and capable of producing at least 1.4 m3 of industrial wood per hectare a year (20 ft3/acre) and is not reserved from timber harvest (Powell et al. 1993). Two-thirds of the nation's forested ecosystems (198 million ha or 490 million acres) are classed as timberland. Because of historical interest in timber production, more information is available for the characteristics of timber inventories on timberland than for other forest land.
Timberland ownership patterns vary throughout the United States. For the country as a whole, 73% of all timberland is owned by private individuals and firms. The remaining 27% is in federal, state, and other public ownerships. Much of the privately owned land is in the East and much of the national forest land is in the West (Fig. 2). Most of the publicly owned land is managed according to plans that account for the various uses and values provided by forest cover. Forest industry lands are generally managed with timber production being the main interest. Other private forest lands are managed for a variety of interests, reflecting the divergent views of the some 6 million owners in this category.

Fig. 2. Timberland ownership patterns by regions, 1992 (Powell et al. 1993).
The nation's timberland contains an estimated 24.3 billion m3 (858 billion ft3) of timber, of which 92% is in growing stock--live, sound trees suited for roundwood (timber) products. Softwoods such as pine are generally used to make lumber and plywood for use in construction. Hardwoods, such as oak, are used in making furniture and pallets. Both softwoods and hardwoods are used in manufacturing paper products. The nation's softwood growing stock volume amounts to 57% of the total, with about 66% of this volume in the West. Total softwood growing stock volume has been slightly declining recently (Fig. 3). By contrast, hardwood growing stock volume increased 7% between 1987 and 1992. More than 90% of all hardwood timber volume is in the eastern United States.

Fig. 3. Softwood and hardwood growing stock volume, selected years (Powell et al. 1993).

Mortality, Growth, Harvest
Mortality is the result of natural causes such as insects, disease, fire, and windthrow. Between 1962 and 1986, mortality averaged 122 million m3 (4.3 billion ft3) per year. Mortality increased to 155 million m3 (5.5 billion ft3) in 1991, but was still less than 1% of the U.S. growing stock volume.
Net annual growth, which already has mortality subtracted out, totaled 612 million m3 (21.6 billion ft3) in 1991--about 2.7% of the growing stock inventory. Total growing stock growth declined about 2% between 1986 and 1991 (Fig. 4), the first decline in net annual growth since 1952. The decline between 1986 and 1991 occurred with softwoods, which declined 4.4% to 339 million m3 (12 billion ft3). Net annual growth for hardwoods increased 0.9%.

Fig. 4. Net annual growth, selected years (Powell et al. 1993).
Removals from timber inventories are losses by other than natural causes (mortality) and include harvest of roundwood products. Timber removals from growing stock inventory in 1991 totaled 461.5 million m3 (16.3 billion ft3) or 2.1% of the inventory. Average timber removals have risen each decade since the 1950's. Almost 55% of all timber removals came from the forests of the South, up from 45% in 1970. Twenty-three percent of all removals came from Pacific coast forests, 17% from the North, and 5% from forests in the Rocky Mountains. Softwoods accounted for two-thirds of all growing stock removals in 1991. Timber removals continued to be concentrated on private land in 1991.
The growth-removals ratio for the United States is greater than one for all species (1.3), for softwoods (1.1), and for hardwoods (1.8), which indicates that the timber inventory is increasing. In the 1920's, timber growth was about one-half the rate of harvest. By the 1940's, improved forest growth rates (partly because of forest protection from fire), as well as declines in harvest rates, resulted in timber growth and harvest coming into approximate balance.
For further information:
David R. Darr
U.S. Forest Service
PO Box 96090
Washington, DC 20090
References
Powell, D.S., J.L. Faulkner, D.R. Darr, Z. Zhu, and D.W. MacCleery. 1993. Forest resources of the United States, 1992. Gen. Tech. Rep. RM-234. U.S. Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO. 132 pp.

 USFS. 1992. Forest Service resource inventories: an overview. Forest inventory, economics, and recreation research. U.S. Forest Service, Washington, DC. 39 pp.


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