Past and Present Land Use and Land Cover in the USA

"Land of many uses," runs a motto used to describe the National Forests, and it describes the United States as a whole just as well. "Land of many covers" would be an equally apt, but distinct, description. Land use is the way in which, and the purposes for which, human beings employ the land and its resources: for example, farming, mining, or lumbering. Land cover describes the physical state of the land surface: as in cropland, mountains, or forests. The term land cover originally referred to the kind and state of vegetation (such as forest or grass cover), but it has broadened in subsequent usage to include human structures such as buildings or pavement and other aspects of the natural environment, such as soil type, biodiversity, and surface and groundwater. A vast array of physical characteristics -- climate, physiography, soil, biota -- and the varieties of past and present human utilization combine to make every parcel of land on the nation's surface unique in the cover it possesses and the opportunities for use that it offers. For most practical purposes, land units must be aggregated into quite broad categories, but the frequent use of such simplified classes should not be allowed to dull one's sense of the variation that is contained in any one of them.

Land cover is affected by natural events, including climate variation, flooding, vegetation succession, and fire, all of which can sometimes be affected in character and magnitude by human activities. Both globally and in the United States, though, land cover today is altered principally by direct human use: by agriculture and livestock raising, forest harvesting and management, and construction. There are also incidental impacts from other human activities such as forests damaged by acid rain from fossil fuel combustion and crops near cities damaged by tropospheric ozone resulting from automobile exhaust.

Changes in land cover by land use do not necessarily imply a degradation of the land. Indeed, it might be presumed that any change produced by human use is an improvement, until demonstrated otherwise, because someone has gone to the trouble of making it. And indeed, this has been the dominant attitude around the world through time. There are, of course, many reasons why it might be otherwise. Damage may be done with the best of intentions when the harm inflicted is too subtle to be perceived by the land user. It may also be done when losses produced by a change in land use spill over the boundaries of the parcel involved, while the gains accrue largely to the land user. Economists refer to harmful effects of this sort as negative externalities , to mean secondary or unexpected consequences that may reduce the net value of production of an activity or displace some of its costs upon other parties. Land use changes can be undertaken because they return a net profit to the land user, while the impacts of negative externalities such as air and water pollution, biodiversity loss, and increased flooding are borne by others. Conversely, activities that result in secondary benefits (or positive externalities) may not be undertaken by landowners if direct benefits to them would not reward the costs.

Over the years, concerns regarding land degradation have taken several overlapping (and occasionally conflicting) forms. Conservationism emphasized the need for careful and efficient management to guarantee a sustained supply of productive land resources for future generations. Preservationism has sought to protect scenery and ecosystems in a state as little human-altered as possible. Modern environmentalism subsumes many of these goals and adds new concerns that cover the varied secondary effects of land use both on land cover and on other related aspects of the global environment. By and large, American attitudes in the past century have shifted from a tendency to interpret human use as improving the condition of the land towards a tendency to see human impact as primarily destructive. The term "land reclamation" long denoted the conversion of land from its natural cover; today it is more often used to describe the restoration and repair of land damaged by human use. It would be easy, though, to exaggerate the shift in attitudes. In truth, calculating the balance of costs and benefits from many land-use and land-cover changes is enormously difficult. The full extent and consequences of proposed changes are often less than certain, as is their possible irreversibility and thus their lasting significance for future generations.

Where Are We?

The United States, exclusive of Alaska and Hawaii, assumed its present size and shape around the middle of the 19th century. Hawaii is relatively small, ecologically distinctive, and profoundly affected by a long and distinctive history of human use; Alaska is huge and little affected to date by direct land use. In this review assessment we therefore survey land use and land cover change, focusing on the past century and a half, only in the conterminous or lower 48 states. Those states cover an area of almost 1900 million acres, or about 3 million square miles.

How land is used, and thus how land cover is altered, depends on who owns or controls the land and on the pressures and incentives shaping the behavior of the owner. Some 400 million acres in the conterminous 48 states -- about 21% of the total -- are federally owned. The two largest chunks are the 170 million acres of Western rangeland controlled by the Bureau of Land Management and the approximately equal area of the National Forest System. Federal land represents 45% of the area of the twelve western states, but is not a large share of any other regional total. There are also significant land holdings by state governments throughout the country.

Most of the land in the United States is privately owned, but under federal, state, and local restrictions on its use that have increased over time. The difference between public and private land is important in explaining and forecasting land use and land cover change, but the division is not absolute, and each sector is influenced by the other. Private land use is heavily influenced by public policies, not only by regulation of certain uses but through incentives that encourage others. Public lands are used for many private activities; grazing on federal rangelands and timber extraction from the national forests by private operators are the most important and have become the most controversial. The large government role in land use on both government and private land means that policy, as well as economic forces, must be considered in explaining and projecting changes in the land. Economic forces are of course significant determinants of policy -- perhaps the most significant -- but they remain to some degree an independent variable.

There is no standard, universally accepted set of categories for classifying land by either use or cover, and the most commonly used, moreover, are hybrids of land cover and land use . Those employed here, which are by and large those of the U.S. National Resources Inventory conducted every five years by relevant federal agencies, are cropland, forest, grassland (pasture and rangeland), wetlands, and developed land.

• Cropland is land in farms that is devoted to crop production; it is not to be confused with total farmland, a broad land- use or land-ownership category that can incorporate many forms of land cover.

• Forest land is characterized by a predominance of tree cover and is further divided by the U.S. Census into timberland and non-timberland. By definition, the former must be capable of producing 20 cubic feet of industrial wood per acre per year and remain legally open to timber production.

• Grassland as a category of land cover embraces two contrasting Census categories of use: pasture (enclosed and what is called improved grassland, often closely tied to cropland and used for intensive livestock raising), and range (often unenclosed or unimproved grazing land with sparser grass cover and utilized for more extensive production).

• Wetlands are not a separate Census or National Resources Inventory category and are included within other categories: swamp, for example, is wetland forest. They are defined by federal agencies as lands covered all or part of the year with water, but not so deeply or permanently as to be classified as water surface per se.

• The U.S. government classifies as developed land urban and built-up parcels that exceed certain size thresholds. "Developed" or "urban" land is clearly a use rather than a cover category. Cities and suburbs as they are politically defined have rarely more than half of their area, and often much less, taken up by distinctively "urban" land cover such as buildings and pavement. Trees and grass cover substantial areas of the metropolitan United States; indeed, tree cover is greater in some settlements than in the rural areas surrounding them.

  By the 1987 U.S. National Resources Inventory, non-federal lands were divided by major land use and land cover classes as follows: cropland, about 420 million acres (22% of the entire area of the 48 states); rangeland about 400 million (21%); forest, 390 million (21%); pasture 130 million (7%); and developed land 80 million (4%). Minor covers and uses, including surface water, make up another 60 million acres (Table 1). The 401 million acres of federal land are about half forest and half range. Wetlands, which fall within these other Census classes, represent approximately 100 million acres or about five percent of the national area; 95 percent of them are freshwater and five percent are coastal.

  These figures, for even a single period, represent not a static but a dynamic total, with constant exchanges among uses. Changes in the area and the location of cropland, for example, are the result of the addition of new cropland from conversion of grassland, forest, and wetland and its subtraction either by abandonment of cropping and reversion to one of these less intensive use/cover forms or by conversion to developed land. The main causes of forest loss are clearing for agriculture, logging, and clearing for development; the main cause of forest gain is abandonment of cropland followed by either passive or active reforestation. Grassland is converted by the creation of pasture from forest, the interchange of pasture and cropland, and the conversion of rangeland to cropland, often through irrigation.

  Change in wetland is predominantly loss through drainage for agriculture and construction. They also include natural gain and loss, but the growing possibilities for wetland creation and restoration are implicit in the Environmental Protection Agency's "no net loss" policy (emphasis added). Change in developed land runs in only one direction: it expands and is not, to any significant extent, converted to any other category.

  Comparison of the American figures with those for some other countries sets them in useful perspective. The United States has a greater relative share of forest and a smaller relative share of cropland than does Europe as a whole and the United Kingdom in particular. Though Japan is comparable in population density and level of development to Western Europe, fully two-thirds of its area is classified as forest and woodland, as opposed to ten percent in the United Kingdom; it preserves its largely mountainous forest area by maintaining a vast surplus of timber imports over exports, largely from North America and Southeast Asia.

  Regional patterns within the U.S. (using the four standard government regions of Northeast, Midwest, South, and West) display further variety. The Northeast, though the most densely populated region, is the most heavily wooded, with three-fifths of its area in forest cover. It is also the only region of the four in which "developed" land, by the Census definition, amounts to more than a minuscule share of the total; it covers about eight percent of the Northeast and more than a quarter of the state of New Jersey. Cropland, not surprisingly, is by far the dominant use/cover in the Midwest, accounting for just under half of its expanse. The South as a whole presents the most balanced mix of land types: about 40 percent forest, 20 percent each of cropland and rangeland, and a little more than ten percent pasture. Western land is predominantly rangeland, with forest following and cropland a distant third. Wetlands are concentrated along the Atlantic seaboard, in the Southeast, and in the upper Midwest. Within each region, of course, there is further variety at and below the state level.

  Where Have We Been?

  The public domain, which in 1850 included almost two-thirds of the area of the present conterminous states, has gone through two overlapping phases of management goals. During the first, dominant in 1850 and long thereafter, the principal goal of management was to transfer public land into private hands, both to raise revenue and to encourage settlement and land improvements. The government often attached conditions (which were sometimes complied with) to fulfill other national goals such as swamp drainage, timber planting and railroad construction in support of economic development.

  The second phase, that of federal retention and management of land, began with the creation of the world's first national park, Yellowstone, shortly after the Civil War. It did not begin to be a significant force, however, until the 1890s, when 40 million acres in the West were designated as federal forest reserves, the beginning of a system that subsequently expanded into other regions of the country as well. Several statutory vestiges of the first, disposal era remain (as in mining laws, for example), but the federal domain is unlikely to shrink noticeably in coming decades, in spite of repeated challenges to the government retention of public land and its regulation of private land. In recent years, such challenges have included the "Sagebrush Rebellion" in the rangelands of the West in the 1970s and 1980s calling for the withdrawal of federal control, and legal efforts to have many land-use regulations classified as "takings," or as exercises of the power of eminent domain. This classification, were it granted, would require the government to compensate owners for the value of development rights lost as a result of the regulation.

  Cropland

  Total cropland rose steadily at the expense of other land covers throughout most of American history. It reached a peak during the 1940s and has subsequently fluctuated in the neighborhood of 400 million acres, though the precise figure depends on the definition of cropland used. Long-term regional patterns have displayed more variety. Cropland abandonment in some areas of New England began to be significant in some areas by the middle of the nineteenth century. Although total farmland peaked in the region as late as 1880 (at 50%) and did not decline sharply until the turn of the century, a steady decline in the sub category of cropland and an increase in other farmland covers such as woodland and unimproved pasture was already strongly apparent. The Middle Atlantic followed a similar trajectory, as, more recently, has the South. Competition from other, more fertile sections of the country in agricultural production and within the East from other demands on land and labor have been factors; a long-term rise in agricultural productivity caused by technological advances has also exerted a steady downward pressure on total crop acreage even though population, income, and demand have all risen.

  Irrigated cropland on a significant scale in the United States extends back only to the 1890s and the early activities in the West of the Bureau of Reclamation. Growing rapidly through about 1920, the amount of irrigated land remained relatively constant between the wars, but rose again rapidly after 1945 with institutional and technological developments such as the use of center-pivot irrigation drawing on the Ogallala Aquifer on the High Plains. It reached 25 million acres by 1950 and doubled to include about an eighth of all cropland by about 1980. Since then the amount of irrigated land has experienced a modest decline, in part through the partial depletion of aquifers such as the Ogallala and through competition from cities for water in dry areas.

  Forests

  At the time of European settlement, forest covered about half of the present 48 states. The greater part lay in the eastern part of the country, and most of it had already been significantly altered by Native American land-use practices that left a mosaic of different covers, including substantial areas of open land.

  Forest area began a continuous decline with the onset of European settlement that would not be halted until the early twentieth century. Clearance for farmland and harvesting for fuel, timber, and other wood products represented the principal sources of pressure. From an estimated 900 million acres in 1850, the wooded area of the entire U.S. reached a low point of 600 million acres around 1920 (Fig. 1). It then rose slowly through the postwar decades, largely through abandonment of cropland and regrowth on cutover areas, but around 1960 began again a modest decline, the result of settlement expansion and of higher rates of timber extraction through mechanization. The agricultural censuses recorded a drop of 17 million acres in U.S. forest cover between 1970 and 1987 (though data uncertainties and the small size of the changes relative to the total forest area make a precise dating of the reversals difficult). At the same time, if the U.S. forests have been shrinking in area they have been growing in density and volume. The trend in forest biomass has been consistently upward; timber stock measured in the agricultural censuses from 1952 to 1987 grew by about 30%.

  National totals of forested area again represent the aggregation of varied regional experiences. Farm abandonment in much of the East has translated directly into forest recovery, beginning in the mid- to late nineteenth century (Fig. 2). Historically, lumbering followed a regular pattern of harvesting one region's resources and moving on to the next; the once extensive old-growth forest of the Great Lakes, the South, and the Pacific Northwest represented successive and overlapping frontiers. After about 1930, frontier-type exploitation gave way to a greater emphasis on permanence and management of stands by timber companies. Wood itself has declined in importance as a natural resource, but forests have been increasingly valued and protected for a range of other services, including wildlife habitat, recreation, and streamflow regulation.

  Grassland

  The most significant changes in grassland have involved impacts of grazing on the Western range. Though data for many periods are scanty or suspect, it is clear that rangelands have often been seriously overgrazed, with deleterious consequences including soil erosion and compaction, increased streamflow variability, and floral and faunal biodiversity loss as well as reduced value for production. The net value of grazing use on the Western range is nationally small, though significant locally, and pressures for tighter management have increasingly been guided by ecological and preservationist as well as production concerns.

  Wetland

  According to the most recent estimates, 53% of American wetlands were lost between the 1780s and the 1980s, principally to drainage for agriculture. Most of the conversion presumably took place during the twentieth century; between the 1950s and the 1970s alone, about 11 million acres were lost. Unassisted private action was long thought to drain too little; since mid-century, it has become apparent that the opposite is true, that unfettered private action tends to drain too much, i.e., at the expense of now-valued wetland. The positive externalities once expected from drainage -- improved public health and beautification of an unappealing natural landscape -- carry less weight today than the negative ones that it produces. These include the decline of wildlife, greater extremes of streamflow, and loss of a natural landscape that is now seen as more attractive than a human-modified one. The rate of wetland loss has now been cut significantly by regulation and by the removal of incentives for drainage once offered by many government programs.

  Developed Land

  As the American population has grown and become more urbanized, the land devoted to settlement has increased in at least the same degree. Like the rest of the developed world, the United States now has an overwhelmingly non-farm population residing in cities, suburbs, and towns and villages. Surrounding urban areas is a classical frontier of rapid and sometimes chaotic land-use and land cover change. Urban impacts go beyond the mere subtraction of land from other land uses and land covers for settlement and infrastructure; they also involve the mining of building materials, the disposal of wastes, the creation of parks and water supply reservoirs, and the introduction of pollutants in air, water, and soil. Long-term data on urban use and cover trends are unfortunately not available. But the trend in American cities has undeniably been one of residential dispersal and lessened settlement densities as transportation technologies have improved; settlement has thus required higher amounts of land per person over time.

  Where Are We Going?

  The most credible projections of changes in land use and land cover in the United States over the next fifty years have come from recent assessments produced under the federal laws that now mandate regular national inventories of resource stocks and prospects. The most recent inquiry into land resources, completed by the Department of Agriculture in 1989 (and cited at the end of this article), sought to project their likely extent and condition a half- century into the future, to the year 2040. The results indicated that only slow changes were expected nationally in the major categories of land use and land cover: a loss in forest area of some 5% (a slower rate of loss than was experienced in the same period before); a similarly modest decline in cropland; and an increase in rangeland of about 5% through 2040. Projections are not certainties, however: they may either incorrectly identify the consequences of the factors they consider or fail to consider important factors that could alter the picture. Because of the significant impacts of policy and of market forces, the role of policy -- notoriously difficult to forecast and assess -- demands increased attention, in both its deliberate and its inadvertent effects.

  Trends in the United States stand in some contrast to those in other parts of the developed world. While America's forest area continues to decline somewhat, that of many comparable countries has increased in modest degree, while the developing world has seen significant clearance in the postwar era. There has been substantial stability, with slow but fluctuating decline, in cropland area in the United States. In contrast, cropland and pasture have declined modestly in the past several decades in Western Europe and are likely to decline sharply there in the future as long-standing national and European Community agricultural policies subsidizing production are revised; as a result, the European countryside faces the prospect of radical change in land use and cover and considerable dislocation of rural life.

  Why Does It Matter?

  Land-use and land-cover changes, besides affecting the current and future supply of land resources, are important sources of many other forms of environmental change. They are also linked to them through synergistic connections that can amplify their overall effect.

  Loss of plant and animal biodiversity is principally traceable to land transformation, primarily through the fragmentation of natural habitat. Worldwide trends in land-use and land cover change are an important source of the so-called greenhouse gases, whose accumulation in the atmosphere may bring about global climate change. As much as 35% of the increase in atmospheric CO2 in the last 100 years can be attributed to land-use change, principally through deforestation. The major, known sources of increased methane -- rice paddies, landfills, biomass burning, and cattle -- are all related to land use. Much of the increase in nitrous oxide is now thought due to a collection of sources that also depend upon the use of the land, including biomass burning, cattle and feedlots, fertilizer application, and contaminated aquifers.

  Land-use practices at the local and regional levels can dramatically affect soil condition as well as water quality, and water supply. And finally, vulnerability or sensitivity to existing climate hazards and possible climate change is very much affected by changes in land use and cover. Several of these connections are illustrated below by examples.

  Carbon emissions

  In most of the world, both fossil-fuel combustion and land transformation result in a net release of carbon dioxide to the atmosphere. In the United States, by contrast, present land use and land cover changes are thought to absorb rather than release CO2 through such processes as the rapid growth of relatively youthful forests. In balance, however, these land-use-related changes reduce U.S. contributions from fossil fuel combustion by only about 10%. The use of carbon-absorbing tree plantations to help diminish global climate forcing has been widely discussed, although many studies have cast doubt on the feasibility of the scheme. Not only is it a temporary fix (the trees sequester carbon only until the wood is consumed, decays, or ceases to accumulate) and requires vast areas to make much of a difference, but strategies for using the land and its products to offset some of the costs of the project might have large and damaging economic impacts on other land-use sectors of the economy.

  Effects on arable land

  The loss of cropland to development aroused considerable concern during the 1970s and early 1980s in connection with the 1981 National Agricultural Lands Study, which estimated high and sharply rising rates of conversion. Lower figures published in the 1982 National Resource Inventory, and a number of associated studies, have led most experts to regard the conversion of cropland to other land use categories as representing something short of a genuine crisis, likely moreover to continue at slower rather than accelerating rates into the future. The land taken from food and fiber production and converted to developed land has been readily made up for by conversion of land from grassland and forest. The new lands are not necessarily of the same quality as those lost, however, and some measures for the protection of prime farmland are widely considered justified on grounds of economics as well as sociology and amenities preservation.

  Vulnerability to climate change

  Finally, patterns and trends in land use and land cover significantly affect the degree to which countries and regions are vulnerable to climate change -- or to some degree, can profit from it. The sectors of the economy to which land use and land cover are most critical -- agriculture, livestock, and forest products -- are, along with fisheries, among those most sensitive to climate variation and change. How vulnerable countries and regions are to climate impacts is thus in part a function of the importance of these activities in their economies, although differences in ability to cope and adapt must also be taken into account.

  These three climate-sensitive activities have steadily declined in importance in recent times in the U.S. economy. In the decade following the Civil War, agriculture still accounted for more than a third of the U.S. gross domestic product, or GDP. In 1929, the agriculture-forest-fisheries sector represented just under ten percent of national income. By 1950, it had fallen to seven percent of GDP, and it currently represents only about two percent. Wood in 1850 accounted for 90 percent of America's total energy consumption; today it represents but a few percent. These trends suggest a lessened macroeconomic vulnerability in the U.S. to climate change, though they may also represent a lessened ability to profit from it to the extent that change proves beneficial. They say nothing, however, about primary or secondary impacts of climate change on other sectors, about ecological, health, and amenity losses, or about vulnerability in absolute rather than relative terms, and particularly the potentially serious national and global consequences of a decline in U.S. food production.

  The same trend of lessening vulnerability to climate changes is apparent even in regions projected to be the most exposed to the more harmful of them, such as reduced rainfall. A recent study examined agro-economic impacts on the Missouri-Iowa-Nebraska- Kansas area of the Great Plains, were the "Dust Bowl" drought and heat of the 1930s to recur today or under projected conditions of the year 2030. It found that although agricultural production would be substantially reduced, the consequences would not be severe for the regional economy overall: partly because of technological and institutional adaptation and partly because of the declining importance of the affected sectors, as noted above. The 1930s drought itself had less severe and dramatic effects on the population and economy of the Plains than did earlier droughts in the 1890s and 1910s because of land-use, technological, and institutional changes that had taken place in the intervening period.

  Shifting patterns in human settlement are another form of land-use and land cover change that can alter a region's vulnerability to changing climate. As is the case in most other countries of the world, a disproportionate number of Americans live within a few miles of the sea. In the postwar period, the coastal states and counties have consistently grown faster than the country as a whole in population and in property development. The consequence is an increased exposure to hazards of hurricanes and other coastal storms, which are expected by some to increase in number and severity with global warming, and to the probable sea-level rise that would also accompany an increase in global surface temperature. It is unclear to what extent the increased exposure to such hazards might be balanced by improvements in the ability to cope, through better forecasts, better construction, and insurance and relief programs. Hurricane fatalities have tended to decline, but property losses per hurricane have steadily increased in the U.S., and the consensus of experts is that they will continue to do so for the foreseeable future.

  Conclusions

  How much need we be concerned about changes in land use and land cover in their own right? How much in the context of other anticipated environmental changes?

  As noted above, shifting patterns of land use in the U.S. and throughout the world are a proximate cause of many of today's environmental concerns. How land is used is also among the human activities most likely to feel the effects of possible climate change. Thus if we are to understand and respond to the challenges of global environmental change we need to understand the dynamics of land transformation. Yet those dynamics are notoriously difficult to predict, shaped as they are by patterns of individual decisions and collective human behavior, by history and geography, and by tangled economic and political considerations. We should have a more exact science of how these forces operate and how to balance them for the greatest good, and a more detailed and coherent picture of how land in the U.S. and the rest of the world is used.

  The adjustments that are made in land use and land cover in coming years, driven by worldwide changes in population, income, and technology, will in some way alter the life of nearly every living thing on Earth. We need to understand them and to do all that we can to ensure that policy decisions that affect the use of land are made in the light of a much clearer picture of their ultimate effects.

  For Further Reading

  Americans and Their Forests: A Historical Geography, by Michael Williams. Cambridge University Press, 599 pp, 1989.

  An Analysis of the Land Situation in the United States: 1989- 2040. USDA Forest Service General Technical Report RM- 181. U.S. Government Printing Office, Washington, D.C., 1989.

  Changes in Land Use and Land Cover: A Global Perspective. W. B. Meyer and B. L. Turner II, editors. Cambridge University Press, 537 pp, 1994.

  "Forests in the Long Sweep of American History," by Marion Clawson. Science, vol. 204, pp. 1168-1174, 1979

  Reviewers

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  Prof. Michael Williams is a geographer at Oxford University, England, who has specialized in the history of initial settlement and landscape evolution in Britain, Australia, and the U.S. Currently he is writing a historical geography of global deforestation from earliest times to the present.

  Dr. Donald W. Jones is an economist in the Energy Division of Oak Ridge National Laboratory in Oak Ridge, Tennessee. His research interests include land-use and location theory and the role of energy in economic development.

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