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United States[1]

David R. Darr

USDA Forest Service retired

W. Brad Smith

USDA Forest Service

Introduction

The main landmass of the United States, situated in mid-North America, has a central plain with hills and low mountains to the east and rugged mountains and wide valleys to the west.  Alaska, on Canada’s western border, is dominated by Pacific and Arctic mountains, central plateau, and Arctic slope.  Hawaii, comprised of tops of a chain of submerged volcanic mountains, lies 1,600 miles west of the mainland in the north Pacific.

Original forests were abundant throughout the Eastern United States, mountainous regions of the interior and coastal west, Hawaii, and non-polar regions of Alaska.  Today, the forests of the United States cover 749 million acres, are split almost evenly east and west of the central plain, and contain over 800 species of trees of which 82 are non-native.  About one-third of the pre-European settlement forest has been cleared, primarily for agriculture during the 19^th century.  Although there have been significant regional changes, the total area of forest land has been fairly stable for nearly 100 years.  Fifty-seven percent of all forest land is privately owned.  Public forest land is dominant in the western United States and private forest land is dominant in the East. About 77 million acres of forest land (10 percent of all U.S. forest land) is reserved from commercial timber harvest in wilderness, parks, and other legally reserved classifications.  This is more than triple the area of reserved forest in 1953, with major increases occurring in the West and Alaska.

The following presents an overview of U.S. forests by various measures of resource condition, a discussion of forest types, and a description of drivers of change in resource condition.  Figure 1, which is linked through an attachment at the bottom of the page, shows the forest subregions or the United States.
 

Measures of Resource Condition

Timberland area.—About 504 million acres (two-thirds of all forest land) is classed as timberland—forest land capable of producing in excess of 20 cubic feet per acre per year and not legally withdrawn from timber production.  Timberland is the source of most of the industrial wood used for products and includes 94 percent of eastern forests, 80 percent of  Pacific Northwest forests, about 50 percent of the forests in the interior West and Southwest, and 10 percent of Alaska’s forests (Smith, et al. 2004).  Since 1953, the area of timberland had a net loss of about 1 percent, or about 5 million acres.  Over the last 5 decades, losses have come primarily from withdrawals of public timberland as wilderness or other reserved forests that do not permit timber harvest, and conversion of timberland to nonforest land use.  Most increases have come from reclassification of marginally productive forests and reversion of abandoned pasture lands. 

Timber inventories.—Growing-stock volume on U.S. timberland increased from 616 to 856 million cubic feet (39 percent) between 1953 and 2002.  Between those years, average growing-stock volume rose by 96 percent in the North, 80 percent in the South, and 42 percent in the Rocky Mountain region (see figure 1 for a map of the regions).  Volume declined in the Pacific Coast region.  The loss of growing-stock volume in the Pacific Coast region is the result of harvesting in older, higher volume stands since 1953 and set asides of large areas of older stands in reserved forests which reclassifies trees in these areas as non-growing stock.  The rate of loss has subsided in recent years as harvesting has been sharply curtailed and total volume for the region has begun to stabilize.  About 57 percent of the volume of growing stock is softwoods, with the remaining 43 percent in hardwoods.  About 90 percent of the hardwood timber is in the Eastern United States,  about 68 percent of the softwood timber is in the Western United States and 22 percent is in the South. 

The net growing-stock volume of U.S. hardwoods increased 37 percent between 1977 and 2002 and by 98 percent between 1953 and 2002.  The volume of hardwoods in diameter classes greater than 20 inches has doubled since 1953, from 26 to 66 billion cubic feet in 2002.  The net volume of U.S. softwoods increased from 432 billion to 492 billion cubic feet (14 percent) between 1953 and 2002.  The slower increase in standing volume for softwoods versus hardwoods is the result of stronger demand for softwood species in wood product manufacture. 

Growth and removals.—Data for the nation as a whole indicate that growth has exceeded removals for both softwoods and hardwoods since the first national statistics were reported for 1952.  In 2001, net growth exceeded removals by 33 percent, meaning the Nation’s forest inventory accrued more volume than it lost by mortality and harvest by nearly one-third.  In the 1920s, timber growth nationally was about half the rate of harvest.  By the 1940s, improving forest growth rates and modestly declining harvest rates resulted in timber growth and harvest coming into approximate balance.  In 2001, growth exceeded removals in all regions of the country.  Nationally, hardwood growth exceeded removals by 42 percent and softwoods by 26 percent.

Harvest of roundwood for industrial use in the United States peaked in 1989 at 15.7 billion cubic feet.  Harvest on public lands, mainly in the West, declined through the 1990s.  Domestic demands for end products were met in part by increased harvest on private lands in the South, decreased exports of logs and lumber, more efficient processing and use of wood, and increased imports, mainly from Canada.  The roundwood equivalent of imports amounted to 20.2 percent of U.S. consumption of industrial roundwood in 1989 and 29.5 percent in 2005.

In 2001, about 64 percent of the volume of timber removals was softwoods and 36 percent was hardwoods, compared with 69 and 31 percent, respectively, in 1986.  This reflects a trend toward rising hardwood removals in response to new product technologies such as oriented strand board that use hardwoods.

Saw logs accounted for 49 percent of growing-stock volume harvested in 2001, veneer logs—9 percent, and pulpwood—35 percent.  The remaining 7 percent was used for fuelwood and other products.  Pulp and composite product (for example, oriented strand board) demand continues to rise, increasing by 25 percent since 1986.

Ownership.--Seventy-one percent of timberland is privately owned and these lands accounted for 92 percent of growing stock removals in 2001.  Historically, companies that owned timber processing facilities also owned timber land.  With few exceptions, large U.S.-owned  companies have divested ownership of this timber land to Timber Investment Management Organizations (TIMOs) or Real Estate Investment Trusts (REITs).  Managers of TIMOs and REITs suggest that they will manage much as forest industry has in the past.  However, the shift in ownership adds additional uncertainty about the stability of ownership of these large, forested tracts (Fernholz, et al. 2007).  The area of public forests amounts to 29 percent of U.S. timberland.  National forests are the largest Federal ownership, making up 19 percent of U.S. timberland, but accounting for only 2 percent of timber harvest in 2001.  National forest timber harvest levels declined by 84 percent between 1986 and 2001 after increasing by 92 percent between 1952 and 1986.  Other public forests made up 10 percent of U.S. timberland and accounted for 6 percent of growing-stock removals in 2001.  Harvest on other public forest lands declined by 14 percent between 1986 and 2001.

Forest Types

A forest type map based on types described by Eyre (1980) was produced from satellite imagery and is available to display the spatial extent and location of forest land in the United States (Smith 2004).  This map may be found online at http://www.nationalatlas.gov/mld/forest1.html.  The following discussion of forest cover types uses the Society of American Foresters classification system which is based on dominant tree species (Eyre 1980).

Forests of the North Region.--Overall, the forests of the North have been relatively stable—showing a 3 percent decline since 1977. Maple-beech-birch (Acer/Fagus/Betula spp.) has increased 40 percent  since 1977 to at 53.8 million acres, surpassing Oak-hickory as the most dominant type in the region.  Oak-hickory (Quercus/Carya spp.) forests encompass 51.9 million acres, an increase of 3 percent since 1977.  Together these two mid-successional types account for nearly half of all northern forests.  These gains have been accompanied by losses in early successional types, such as spruce-fir (Abies spp./Picea spp.) down 19 percent (4 million acres) and aspen-birch (Populas spp./Betula spp.) down 12 percent (2.5 million acres).  Perhaps the most dramatic change in the region is the 40 percent loss (9 million acres) of elm-ash-cottonwood (Ulmus spp./Fraxinus spp./Populus spp.).  The reason for this loss is primarily agricultural conversion and flooding of lowlands for reservoirs.  As a result of flood control projects, some of the drier sites have probably transitioned to maple-beech-birch.

Forests of the South Region.—Overall, the forests of the South have been very resilient showing a 3 percent increase (7.5 million acres) since 1977.  In the South, oak-hickory (Quercus/Carya spp.) forests dominate the landscape, covering 80.3 million acres or 37 percent of all forest land.  These forests increased 30 percent between 1977 and 2002.  The second most dominant type in the region is loblolly-shortleaf pine (Pinus taeda and echinata).  This pine has been favored for planting of industrial plantations.  Longleaf-slash pine forests (Pinus palustris and elliottii) cover 13.6 million acres, having declined 3.5 million acres between 1977 and 2002.  These forests have declined steadily for nearly five decades as a result of fire suppression and conversion to the more commercially favored loblolly pine.  Plantation forestry is important in the South and plantations account for 47 percent of all pine forests in the region.  The area of the mixed forests of oak-pine (Quercus/Pinus spp.) and oak-gum-cypress (Quercus/Nyssa/Taxodium spp.) has remained stable since 1977 at 59 million acres.

Forests of the Rocky Mountain Region.—Overall, the forests of the Rocky Mountain Region have been relatively stable, increasing by 3.2 million acres or 2 percent since 1977.  With the exceptions of western white pine (Pinus monticola) and larch (Larix spp.), the forest landscape did not change significantly between 1977 and 2002.  The western white pine and larch types lost a combined 43 percent of their acreage during this time period.  Other smaller percentage loses came in ponderosa (Pinus ponderosa) and lodgepole pine (Pinus contorta) types at 1 and 13 percent respectively.  Much of this loss comes as a result of decades of fire suppression and transition of these types to other dominant covers, particularly fir-spruce (Abies spp./Picea spp.) at the higher elevations and Douglas-fir (Pseudotsuga menziesii) at mid-elevations.

Forests of the Pacific Coast Region.—Overall, the forests of the Pacific Coast Region declined by 1.3 million acres (1 percent) between 1977 and 2002.  Like the Rocky Mountain Region, the western white pine and larch types are relatively small in area, but they declined a combined 33 percent (300,000 acres) between 1977 and 2002.  Douglas-fir declined 7 percent to 19.5 million acres and ponderosa pine declined 10 percent to 14.2 million acres.  The area of fir-spruce declined 41 percent from 13.5 to 7.9 million acres.  Increases came in the hemlock-Sitka spruce type and the combined broadleaves and chaparral types.

Drivers of Change in the Resource Situation

Changing population dynamics, globalization of market forces, climate change, increasing urbanization, and changing technologies are all important drivers of change affecting renewable resource conditions in the United States (USDA Forest Service 2007).

Population growth.—Population growth will have a profound effect on renewable resource conditions in terms of demands for food, fiber, and water as well as demands for living space and land and water for recreational activities.  Projections from the U.S. Bureau of the Census (2004) suggest that there will be more than 400 million people in the United States by 2050, up from 300 million in 2006.  As average per-capita income is expected to outpace inflation, there is little doubt that demands for goods and services from forests and rangelands will continue to grow.

Globalization.—Globalization of market forces continues to affect U.S. resource conditions; for example, much of the U.S. furniture industry has moved to other countries, especially China, while the United States increasingly imports wood products, especially from Canada.  As a result, there is less domestic harvest in the United States, less revenue from the sale of timber, and less incentive for people to manage forests, especially those that are privately owned.  The roundwood equivalent of all U.S. imports (all products—logs, lumber, pulp, paper, etc.) used to make wood products in other countries as a percent of U.S. consumption (production plus imports minus exports) of industrial roundwood increased from 13 percent in 1965 to 30 percent in 2005 with implications for all measures of forest resource condition in the United States—growth, removals, extent of growing stock and forest land, species composition, etc.

Climate change.—Climate change has the potential to fundamentally alter the large-scale distribution of U.S. forest land and rangeland ecosystems, their species diversity, their productivity, and their ability to supply ecosystem services (USDA Forest Service 2007).  There will likely be changes in weather patterns, extreme climate events, and changes in the seasonality of weather.  As climate changes advance, there are indications that there will be increases in disturbances such as forest fires, drought, and insects such as the bark beetle attack in British Columbia.  The diversity of trees, birds, mammals, amphibians, and reptiles may change dramatically under projected changes in climate.  Natural resource managers are beginning to bring the consideration of climate into management through institutional processes such as assessment, monitoring, focused research, education, planning, field-based activities, and mitigation.

Urbanization.—U.S. area classified as urban land is projected to grow from 3.1 percent today to 8.1 percent in 2050 (Nowak and Walton 2005), reflecting the projected growth in U.S. population.  While urban forests can provide some of the same benefits—such as recreation, wildlife habitat, and carbon sinks for cleaner air—urban development forever changes the character of ecosystems. 

Technological change.—The pace of technological change that affects the way wood is grown, processed, and used has quickened over the past several decades.  The internet and other information sharing technologies have enabled globalization and its effects on measures of U.S. forest resource conditions.  Cloning and other ways of enhancing productivity have enabled faster growing plantations—a key source of fiber supply now and in the future.  More product is produced from the same amount of raw material thanks to technological changes in wood processing and less material is left in the woods as residue.  More  efficient use of wood in house construction and other end uses tends to minimize the amount of wood needed to meet consumer demand.

References

Eyre, F.H., 1980, Forest Cover Types of the United States and Canada: Society of American Foresters, 148p.

Fernholz, K.; Bowyer, J.; Howe, J. 2007. TIMOs & REITs: What, why, & how they might impact sustainable forestry. Dovetail Partners, Inc. www.dovetailinc.org. (May 2007)

Nowak, D.J.; Walton, J.T. 2005. Projected urban growth (2000-2050) and its estimated impact on the U.S. forest resource.  Journal of Forestry. 103(8): 383-389.

Smith, B.W.; Miles, P.D.; Vissage, J.W.; Pugh, S.A. 2004. Forest resources of the United States, 2002: a technical document supporting the USDA Forest Service 2005 nupdate og the RPA Assessment. Gen. Tech. Rep. NC-GTR-241. St. Paul, MN: USDA Forest Service , North Central Research Station. 137 p.

Smith, B.W. 2004. Criterion 1—Indicators 1, 2, 3, 4: Conservation of biological diversity. In: Darr, D.R., coord. Data report: a supplement to the national report on sustainable forests—2003. FS-766A. Washington, DC: USDA Forest Service. http://www.fs.fed.us/research/sustain (December 2006).

U.S. Bureau of the Census. 2004. National population projections. http://www.census.gov/population/www/projections/natsum-T1.html.

USDA Forest Service. 2007. Interim update of the 2000 renewable resources planning act assessment. FS-874. Washington, DC. 113 p.

Posted 18 August 2007

Updated 22 August 2007; V2

Figure 1. – Major Forest Reporting Regions and Subregions of the United States (linked at the bottom of the page)