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Land Development and Conversion: Developed Countries

Ralph Alig

Pacific Northwest Research Station, USDA Forest Service

Introduction

Conversion of rural lands to developed uses in the form of deforestation has had large impacts on forest ecosystems. Conversion of forests can threaten the ability of diverse forestland-based ecosystems to provide a variety of habitats for wildlife; help to cleanse the air and water; supply timber, fuelwood, and other harvested products; serve as places for recreation; and provide other goods and environmental services such as mitigation of global climate change (Alig et al. 2006). Forest ecosystems range from pure forest to urban forests. An increasing number of structures (e.g., houses) pose increased costs of fire suppression and potential loss of substantial asset values. Long-term assessment of the condition of forests and of the relationships between forest conditions and socio-economic factors related to deforestation is key in defining policy questions and actions needed to sustain forest-based services.

Setting and Trends

Determining the extent of human settlements across developed countries presents a challenge, as definitions of “developed,” “built-up,” and “urban” land vary greatly (Alig and Healy 1987), particularly among nations. Human settlements vary widely in density (e.g., Alig et al. 2004), form, and distribution. In North America, urban settlements, as they have been defined by the census bureaus of each nation, contain most of the population. Approximately 75-80 percent of the population of the continent is urban as defined by the census bureaus of the U.S., Canada, and Mexico, and this proportion is projected to continue to increase . Even within North America, U.S., Canadian, and Mexican census definitions are not consistent; and several other classification schemes for defining and mapping settlements have been developed (such as the U.S. Dept. of Agriculture’s National Resource Inventory (NRI) categorization of developed land, as well as a variety of methods based on satellite imagery). One method of coarsely approximating settled land cover at a continental scale is the Global Rural-Urban Mapping Project . This method, which is based on nighttime lights satellite imagery, estimates 1,039,450 km² or almost 5 percent of the total continental land area to be developed, similar to the 5.2 percent estimate in 1997 by the USDA’s NRI (USDA NRCS 2001) of developed area for the U.S.’s 48 contiguous states.

Given the lack of sufficient definitions and data across countries, we concentrate on the case of the United States because it has relatively good data coverage for developed land. U.S. developed land covers approximately 5 percent of nonfederal land area, at least ten times the percentage of developed land in Canada, which is the other major forest products producer in North America. Total developed area is about 100 million acres for the U.S.’s 48 contiguous states (USDA NRCS 2001). The largest increases in U.S. developed area in recent decades have been in the southeastern region of the country (13 States from Virginia to Texas). Aside from the U.S. as a whole, this region provides more timber harvest than any other country in the world (Wear and Greis 2002). Between 1982 and 1997, the U.S. South had seven of the ten states with the largest average annual additions of developed area according to the USDA (NRCS 2001). The top three--Texas, Florida, and North Carolina--each added more developed area than did the country’s most populous state, California.

Two major data sources show a steady increase in U.S. developed area in recent decades. Estimates by the first source, U.S. Census Bureau, extend farthest back in time, and show at least a doubling in census-defined urban area between 1960 and 2000. Census urban area is comprised of all territory units in urbanized areas and in places of more than 2,500 persons outside of urbanized areas. The Census measure of urbanization labels as “built-up” some land that is still to some extent available for rural productive uses, thereby probably erring on the side of overgenerous inclusion (Alig and Healy 1987). Although the term “paved over” has frequently been used to describe urban land, only a small part of the land so classified is literally paved.

The other major data source is the NRI (USDA NRCS 2001). The NRI estimate of U.S. developed area increased 34 percent between 1982 and 1997, with an acceleration in the 1990s that was more than 50 percent higher than that of the previous measurement. Between 1982 and 1997, developed area as a percentage of the total land area in the 48 contiguous States increased from 3.9 percent to 5.2 percent. Outside urban areas, the NRI also includes developed land occupied by nonfarm rural built-up uses (e.g., rural transportation land), which are not included in the Census urban category.

A significant amount of low-density development has been part of the expansion in developed area. Between 1982 and 1997, the U.S. population grew by 17 percent, while urbanized area grew by 47 percent. The amount of area per person dedicated to new housing has almost doubled in the last 20 years. Since 1994, 55 percent of the total U.S. developed land has been developed as 10+ acre housing lots and 90 percent as 1+ acre lots. Eighty percent of all new development has been outside existing urban areas (i.e., nonmetro areas) and not used for farm housing (USDA ERS 2006). For the South in particular, the region with a large amount of private timber harvest and substantial biodiversity, the increment in developed area for each new resident has been increasing (Alig et al. 2004), resulting in lower density development. A contributing factor there and in other regions is the decreasing number of people per household (Alig et al. 2003), due to decreasing family size, popularity of second homes, divorce rate, and growing number of older adults living in single homes or alone.

Low-density development in rural areas means that development brings more people living closer to remaining forest lands. Based on nationwide rural-urban continuum classes (Smith et al. 2004), 13 percent of U.S. forest land now is located in major metropolitan counties and 17 percent in intermediate and small metropolitan counties and large towns, together making up 30 percent of all U.S. forest land (Smith et al. 2004). Between 1997 and 2002, the forest area in major metropolitan areas increased by 5 percent, or more than 5 million acres, as U.S. developed area expanded considerably. For the whole U.S., more than one-quarter of counties are currently classified as metropolitan. That compares with less than one-tenth 50 years ago.

Amount of urban land added per additional person is higher for non-metropolitan counties. Some Americans have a preference living in less-congested areas and will commute additional minutes or hours to realize their goals, made possible by the U.S.’s excellent road system. Moreover, an increasing population of retirees has augmented out-migration from central cities and suburbs to rural areas that offer aesthetic amenities. Natural amenities may be a more important determinant of population growth than nearness to metropolitan centers or type of local economy (McGranahan 1999). Amenity migration also has contributed to additional stresses in coastal ecosystems. Coastal areas are more urban than other ecosystems, for example, and even rural populations in coastal ecosystems are much denser than in other rural areas.

Conversion of Forests

The long-term historical loss in U.S. forest area since the early 1950s has been due to a combination of factors, but in more recent decades has been primarily due to conversion to urban and developed uses (Alig et al. 2003, 2004). Deforestation is the conversion from forest to nonforest use, and between 1982 and 1997, 23 million acres were deforested on nonfederal land in the United States. The destination of about half of the converted forest acres was to urban and developed uses, with more than 10 million acres of U.S. nonfederal forests converted to developed uses according to NRI estimates. That is an area larger in size than the combined current forest area of five northeastern states (Connecticut, Delaware, Maryland, New Jersey, and Rhode Island). Between 1992 and 1997, the proportion of urban and developed uses as a destination for deforested acres increased to 55 percent of the total deforestation (USDA NRCS 2001), with about one million converted to developed uses per year. Some forestland is projected to continue to be converted to agricultural uses but opportunities exist for substantial afforestation, including enhanced amounts if government farm programs are reduced (Alig et al. 1998).

Net changes (area into forest minus area out of forest) are typically much smaller than total or gross changes (area into forest plus area out of forest). Gross area changes totaled about 50 million acres involved in the multiple pathways of land use change for nonfederal forests for the contiguous 48 states between 1982 and 1997 (USDA NRCS 2001). The gross change in forest area was 14 times as large as the net change in forest area. When forests are converted to other uses, the new forest area taking its place elsewhere does not necessarily provide the same ecosystem services because acres exiting (e.g., deforestation) or entering (e.g., afforestation) the forestland base can represent quite different forest conditions, so that distinctions between net and gross changes in forest area are important.

In addition to settlement pattern and overall population growth, amenity-based migration has contributed to interregional shifts in population, with the West growing faster than the national average. For example, a growing number of “ranchettes” and subdivisions has been particularly evident in the Rocky Mountain region. Inmigration has resulted in many residents desiring forested settings, resulting in construction of primary or secondary homes in forests or on rangelands. The Rocky Mountain region also had the highest amount of developed area per additional person between 1992 and 1997 (Alig et al. 2004, USDA NRCS 2001).

Projections

Urban and developed areas are projected by econometric models to continue to grow substantially, in line with the projected U.S. population increase of more than 120 million people over the next 50 years and higher average levels of personal income (e.g., Alig and Plantinga 2004, Alig et al. 2004). Developed land will also increase in other parts of the developed world because of the global increase in population from 6 to 9 billion by 2050. U.S. developed area is projected to increase by 79 percent, raising the developed proportion of the total land base from 5.2 percent to 9.2 percent (Alig et al. 2004). Projections based upon Census Bureau data indicate similar substantial increases in urban area (Nowak and Walton 2005).

Total forest-land area in the United States is projected to decrease on net by approximately 23 million acres between 1997 and 2050 (Alig et al. 2003), examined as part of periodic national assessments of forest and rangeland ecosystems. This would be a 3 percent reduction. The main reason for the projected reduction in forest-land area is the conversion to urban and developed uses. Along with that, additional housing density on remaining forestland is projected to be substantial (Stein et al. 2005), with an increase from either rural or ex-urban to urban (22 million acres) or from rural to ex-urban (22 million acres). Continued development will also further fragment forests (e.g., Wear et al. 2004).

Summary

Concerns about reduction in forest area are of long standing, with some of the earliest efforts in forest conservation inspired by rapid loss of forests to agriculture and logging, the desire to protect timber and water resources, and to preserve lands of extraordinary beauty and uniqueness. The amount of developed land in developed countries has been increasing, and continued expansion is projected. Using the United States as an example, socio-economic drivers of land use change such as population and personal income levels have increased substantially on average since World War II and have driven increases in land development. Human land use is the primary force driving changes in forest ecosystem attributes. Nationwide, more than 60 percent of housing units built in the 1990s were constructed in or near wildland vegetation (Radeloff et al. 2005). More than 44 million acres of private forest are projected to experience housing density increases, with most of the most heavily impacted watersheds in the East. Looking ahead, the U.S. population is projected to grow by more than 120 million people by 2050, with more than 50 million acres of U.S. forestland projected to be deforested by 2050.

Land-use changes affecting U.S. forests since 1990 have been concentrated in the South, the region having more timber harvest than other country. Land base changes can affect the U.S. South’s ability to continue its growing role in softwood timber supply, and recent surveys (e.g., Brown 2004) and the USDA NRCS national resource inventory (2001) suggest that loss of timberland to urbanization is accelerating in key timber supply regions. For example, expansion of developed area and urban sprawl in the South has been described as a major issue for future natural resource management, especially for the region’s forests (Wear and Greis 2002). Projections of continued substantial shifts to urban and suburban developed land are based on projected significant increases in the U.S. population and real personal income levels (Wear and Greis 2002, Alig et al. 2004).

When an area is converted to urban and built-up uses, it is likely to be an essentially permanent conversion. Development also affects quality of remaining forests due to fragmentation (e.g., Butler et al. 2004, Alig et al. 2005, Wear et al. 2004). More people on the forested landscape often means loss of open space and concern over loss of the amenity values generally associated with open space. The growing concerns about the loss of forest land to development have also been reflected in public and private efforts to preserve forest land as open space (Kline et al. 2004). Because much of the growth is expected in areas that are relatively “stressed” with respect to human-environment interactions, such as some coastal counties, implications for landscape and urban planning include potential impacts on sensitive watersheds, riparian areas, wildlife habitat, open space, and water supplies.

References

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Alig, R. and A. Plantinga. Future forestland area: Impacts from population growth and other factors that affect land values. J. Forestry 102 (8; 2004): 19-24.

Alig, R.; Adams, D.; McCarl, B. Impacts of Incorporating Land Exchanges Between Forestry and Agriculture in Sector Models. J. of Agricultural and Applied Economics, 30,2 (Dec. 1998): 389-401.

Alig, R., A. Plantinga, S. Ahn, and J. Kline. Land use changes involving forestry for the United States: Recent trends and projections. USDA Forest Service Gen. Tech. Report 587, Pacific Northwest Research Station. Portland, OR. 92p. 2003.

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Alig, Ralph; Stewart, Susan; Wear, David; Stein, Susan; Nowak, David. Conversions of Forestland: Trends, Determinants, Projections, and Policy Considerations. Chapter X in “Threats to forest ecosystems.” USDA Forest Service (in press). Southern Research Station. 2006.

Brown, M.J. Forest statistics for North Carolina, 2002. Resour. Bull. SRS–88. U.S. Department of Agriculture, Forest Service, Southern Research Station, Asheville, NC. 2004.

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Posted: 22 April 2006