Projections from different studies, (e.g., Resources Planning Act Assessments) are summarized next and compared where appropriate. Land use projections are generally prepared by obtaining projections of the independent variables and then simulating the impacts of projected conditions on future land uses (Table: Sources of land-use projections). Projections can be implemented to contrast the potential effects of policy or market changes with historical usage (counterfactual simulations, e.g., Lubowski and others 2006) or to project future land uses over a range of scenarios (e.g., Alig and others 2003). Projection exercises have indicated that future land uses are especially sensitive to changes in population density, income, and agricultural and timber prices and production costs.

Urban and developed areas are projected to continue to grow substantially in line with the projected population increase of more than 120 million people over the next 50 years (Alig and others 2004). This will be part of a global increase in population, as the world’s population is projected to grow from 6 to 9 billion by 2050. U.S. developed area is projected to increase by 79 percent, raising the proportion of the total land base that is developed from 5.2 percent to 9.2 percent. Projections based upon Census Bureau data indicate similar substantial increases in urban area. Urban land in the United States is projected to increase from 3.1 percent in 2000 to 8.1 percent in 2050, an area of about 97 million acres, which is larger than the state of Montana. Most of the urban growth is projected to occur around the more heavily urbanized areas, with significant expansion in the East and along the west coast.

Population and income pressures on land uses are not uniform across the Nation. For example, population has shifted from the North to the South and the West in recent decades. Because much of the growth is expected in sensitive areas already burdened by anthropogenic impacts, such as some coastal counties, implications for landscape and urban planning include potential impacts on sensitive watersheds, riparian areas, wildlife habitat, and water supplies. Although providing additional living space and infrastructure, added development may also diminish agricultural output by reducing farmland and changing ecological conditions by converting and fragmenting forests and other natural landscapes. The projected developed and built-up area of about 175 million acres in 2025 represents an area equal to 38 percent of the current United States cropland base, or 23 percent of the current United States forestland base. In line with recent historical trends, the South is projected to continue to have the most developed area through 2025 (Alig and others 2004).

Total forestland area in the United States is projected to decrease on net by approximately 23 million acres, or 3 percent between 1997 and 2050 (Alig and others 2003). Projections of forestland area are related to those above for the other major land uses. The main reason for the projected reduction in forestland area is conversion to urban and developed uses associated with the projected increases in population and income discussed earlier.

The projected reduction in forestland is consistent with earlier studies, (e.g., USDA Forest Service 1988). The notable reductions in the South are generally consistent with the regional assessment of the southern forest resource situation, indicating that urbanization, among all forces of change, will have the most direct, immediate, and permanent effects on the extent, condition, and health of forests in the South (Wear and Greis 2002). Projections estimate that tens of millions of acres of forests in the region will be lost to urbanization from 1992 to 2040. The 13 States in the South are projected to have an overall net decline of only 2 percent in forest area because some farmland will be converted to forests. Timberland area is projected to increase in the South-Central region, where much land is suitable for use in either agriculture or forestry, as a consequence of conversion of agricultural land to forest. Such conversion is to be expected if it is assumed that real prices for agricultural commodities fall and agricultural subsidies and related programs are reduced.

The largest forest area losses in the South are projected for the Southeast. Forestland at the periphery of urban areas is likely to be developed. For example, in Georgia about 5.6 million acres of forests may be converted to developed uses by 2010. It is conservatively estimated that as much as 26 percent of the timber-growing stock measured in the 1997 Georgia inventory could be affected (Wear and Newman 2004).

Projections for other regions of the country largely follow recent historical trends (Alig and others 2003). Most of the losses are projected to be on NIPF lands.

We compared land use projections from models by Lubowski and others (2006) and Hardie and others (2000). We use these models to project land uses in the Southeastern United States to the year 2020. Using two separate models allows us to examine potential differences based on modeling structure. The Lubowski and others model estimates transitions or changes in land uses, whereas the Hardie and others model estimates the equilibrium land use shares in each period. Both models summarize land uses at county level and are based on measures of land uses from the National Resource Inventory (NRI). The 1997 NRI survey serves as the base year for projections.

Projections for the South as a whole show a significant continuation of urbanization and are consistent with the Nowak and others (2006) projections and separate projections by Alig and others (2004). Urban area in the South is projected to increase under all scenarios.

Year 2020 forestland area projected by the model of Lubowski and others is similar to those generated by the model of Hardie and others under a high timber price scenario. The Hardie and others model projects that forestland area in the South could fall as much as 20 million acres under a low timber price scenario. Econometric land use models are generally effective tools for projecting forest area; but an important consideration is whether there are any changes in the underlying structural relationships over the historical or projections periods, analyzed using statistical methods to test for changes, (e.g., significant policy environment alteration) in model parameters over time (Ahn and others 2000).

Relatively few studies have projected forest fragmentation, especially at larger scales. One example of a broader scale study is in Wear and others (2004) where changes are forecasted in interior forest for each county in the South, a region where recent trends include significant land use change. Wear and others, who based forest fragmentation projections on population density forecasts to the year 2020, assumed that relative returns to agricultural and timber production would remain at current levels. Under this scenario, the South as a whole is forecast to lose 747,000 ha (1.85 million acres), or about 2.12 percent of interior forest cover.

These changes are not constant across the region. Among ecological sections, the Southern Appalachian Piedmont would lose the greatest area of interior forest cover (173,166 ha or 427,903 acres). The gulf prairies and marshes in Texas, which have very little interior forest, would lose the greatest proportion of interior forest (56.7 percent) (Wear and others 2004). The second and fourth greatest reductions are projected for the eastern and western Florida coastal lowlands, respectively. Aggregation to the ecological province level indicates that the Outer Coastal Plain would experience the greatest reduction in interior forest. All ecological sections with losses forecast at greater than 2 percent are located either on the Atlantic and Gulf Coastal Plain or in the upland areas of North Carolina, Virginia, Tennessee, and Kentucky.

The distribution of forecast losses of forest interior between urban and rural counties was examined further. Urban counties were defined as those attached to metropolitan statistical areas (MSAs) by the Office of Management and Budget, and rural counties were defined as the remainder. The MSA counties contain 492,690 ha (1,217,463 acres) or 66 percent of the total forecast loss of 747,744 ha (1,847,716 acres). (Heavily impacted MSAs are concentrated in Florida. The Tampa-St. Petersburg-Clearwater MSA is forecast to lose 34.5 percent of its interior forest, and 7 of the 10 MSAs with the highest percentage losses are found in Florida. Columbia (South Carolina), Atlanta (Georgia), and Raleigh-Durham-Chapel Hill (North Carolina) round out the top 10.

Projections of housing density increases on forestland were made in the Forests on the Edge study discussed in section 1. This project has ranked watersheds across the conterminous United States according to the percentage of each watershed that contains private forest projected to experience increased housing density (Stein and others 2005; Theobald 2005). Three housing density thresholds were identified: rural (no more than 15 units for every square mile); urban (at least 64 units per square mile); and ex-urban (16 to 63 units per square mile). Areas identified as having a substantial increase (44 million acres in total) were those where housing was projected to increase from either rural or ex-urban to urban (22 million acres) or from rural to ex-urban (22 million acres). Watersheds included in the assessment had at least 10 percent forest cover with a minimum of half private land.

Note that for the WUI research, projections of WUI growth, 2010 to 2030, will be made by Northern Research Station scientists and collaborators as soon as the housing density projections on which they are built have been completed. WUI projections will assume that vegetative cover will remain constant through 2030.

Most watersheds projected to experience the greatest amount of change were located in the East, although some were located in the Great Lakes area, California, and the Pacific Northwest. The greatest change will be in 12 States in the Northeast and South (Stein and others 2005). A study in progress is identifying watersheds where private forests contribute most to water quality, timber, interior forest, and at-risk species habitat and determines where these contributions may be most affected by factors such as housing increases, fire, air pollution, insect pests, and disease. As discussed in a case study at this conference, private forested watersheds most affected are generally found in the East and along the West Coast (Stein and others 2006). Stresses on forest environmental conditions can be compounded if more people live on the remaining forestland as the United States population density continues to increase. The U.S. had about 80 people per square mile of land in 1999 (USDC Census Bureau 2001) in comparison to about 5 people per square mile in 1790.