LAND USE

Humans use the foundation of land for dwellings, the crops of land for eating, the grass of land for grazing, and the timber of land for building. Land brings with it the minerals and fuel beneath, and it receives humanity's waste. People fight over land. Although environmental ethics strengthen human support for natural animals and plants in their competition for habitat, human dominion over the land still leaves for nature only what humanity spares from its own uses. Logically, land cover differs from land use, but it is useful to think of the covers of urban settlement, crop, grass, and forest as four classes or possibilities of land use.

A simple equation connects land use to population times average food requirement divided by food yield per unit area. The German geographer and geologist Albrecht Penck (1858–1945) wrote this equation in a journal of geopolitics in 1924. Earlier the English economist T. R. Malthus (1766–1834) phrased humanity's dependence on food from land in dynamic terms when he wrote that the slow addition of food from land would limit humankind's exponential multiplication.

Location

Before considering global land use in simple equations, the factor of location must be considered. In 1826 the Mecklenburg landowner and economist Johann von Thünen (1783–1850) published Isolated State, a work that introduced location into a model of a conceptually isolated land area surrounding a city. Accessibility was added to the well-known factors of soil and climate that determined land use. Von Thünen assumed, of course, that farmers would maximize their incomes by considering yield, price, and production expense. To these, however, he added the distance to market multiplied by transportation and produce-deterioration rates. The transport cost to the central city of his isolated state creates concentric zones. In the inner zone, gardening prevails but falls off in a short distance because fruit and vegetables deteriorate, and deterioration is part of transport cost. The low value of critical but bulky wood and hay restricts their production to the next zone. A dried crop containing many calories is worth many dollars per ton and does not deteriorate. Hence such crops as grain or onions grow in the third zone. Because cattle go to market on their own legs, the pastoral zone lies farthest from the city.

Beyond raising yields and cutting expenses, farmers soften von Thünen's law in other ways. Trains, trucks, and airplanes cheapen transport, while refrigeration slows deterioration, lowering the obstacle of distance. Nevertheless, as famine in isolated regions can still demonstrate, that the obstacle persists.

Urban Habitat

Location in the city itself imparts a value to developed or urban use that trumps other uses. An ancient city pressed upon local resources and demanded inventions in farming and transport not required by roaming hunters and fishers. A city could finance and build canals, roads, and irrigation, which scattered people could not. Urban use persists, as a ruin like a Roman road attests, whereas crops, grass, and trees can replace one another. Because urban use trumps and outlasts others, it is fortunate, as Ester Boserup argued, that paving and companions elicit

FIGURE 1

more cleverness and invention than wilderness and solitude.

The intensity of urban use is indicated by the area in hectares developed or urbanized per thousand population. Assuming that the area of large cities is fully urbanized, one can calculate the area per thousand persons as less than 4 hectares in Mumbai (Bombay), India, and in Hong Kong in the 1990s. Focusing on smaller areas lowers the estimate of urban use: In 1995 the average use of land per thousand persons in New York City's five boroughs was 11 hectares; on the island of Manhattan, it was only 5 hectares. Twenty-four U.S. counties, including New York in the East and San Francisco in the West, as well as counties in Michigan and Minnesota in the North and Louisiana and Florida in the South, used fewer than 100 hectares per thousand inhabitants–that is, they had population densities of more than 1,000 persons per square kilometer.

Urban use encompasses more than dwellings. In the United States, for example, it includes industrial, commercial, and institutional land; construction and waste disposal sites; railroad yards, airports, and urban transport ways; cemeteries and golf courses; and water structures. The development of land in 49 U.S. states (omitting Alaska) demonstrates that urban use does not increase in proportion to population (see Figure 1). Thus rich as well as poor congregate and use little urban land, making city dwellers, despite their generally higher incomes, the most sparing of land.

At the same time that people congregate on one scale, however, they diffuse on another. Thus in the United States from 1920 to 1990, while the urban proportion grew, the number of persons per occupied housing unit declined from an average 4.3 to2.7. Persistently willing to travel an hour a day in their journey to work while transport speeds increase, people spread from central cities over everlarger metropolitan regions, building suburbs. During the 1990s, the population of metropolitan areas of 2 to 5 million people outgrew that of both more and less populous areas. From 1950 to 1990 urban land expanded at 2.8 percent per year versus total population growth of 1.2 percent, but in 1990 urban use still occupied less than 4 percent of all U.S. land. These trends are echoed in another developed nation, the Netherlands. And some slowing of the growth of urban land use can be seen in both countries.

Cropland

Of the calories and protein supporting people worldwide, 84 percent of the calories and 75 percent of the protein are from crops. Because many animals, bred for human consumption, eat crops, the dominance of crops exceeds even these high percentages. Nevertheless, such a simple proportionality as Penck envisioned between cropland and population must be modified. Dimensions prove that the forces on the right side of the following equation must be identical to the expanse of cropland:

Cropland = Population × Income × Appetite × Yield

where cropland is area in hectares, income is gross domestic product (GDP) per person, appetite is food production divided by GDP, and finally what is termed yield is cropland in hectares divided by food production. This identity implies an independence of the forces. Nevertheless, per capita food consumption rises as income increases, but not in proportion to the rise of income, causing the force of appetite (food per GDP) to fall.

Since 1960, the annual growth of the first force, global population, has slowed from above 2 percent to appreciably below 2 percent. Growth of income also slowed from more than 3 percent to below 2 percent per year. As income rose, the appetite ratio fell. The final force, cropland over food production, fell rather steadily at 2 percent per year. The net of these forces is the rate of expansion of cropland. From 1961 to 1997 cropland expansion averaged about 0.33 percent per year. The decline of the appetite and yield ratios moderated the impact on cropland area that Penck's simple equation would have predicted. The negative income elasticity of the appetite ratio tempered the effect of rising income and, in combination with farmers' improving yields, spared natural habitat from crop use. While benefiting nature, this sparing also benefited humankind, because the area of prime land suitable to be converted to crops is limited.

Grassland

The Food and Agriculture Organization (FAO) reports a category of land use called "permanent pastures," which it defines as land used permanently (five years or more) for herbaceous forage crops, either cultivated or growing wild, but apologizes that the dividing line between this category and "forests and woodland" is rather indefinite. In 1993 permanent pasture comprised 26 percent of global land, slightly more than twice the total area of cropland, slightly less than that of forests and woodlands, and slightly more than the land unaccounted for by FAO.

Demand for the protein in the meat and milk of grazing animals might seem to connect pasture to population. The change in human and animal populations, animal protein production, and the land used for pasture, however, proves that the connection is not a simple proportionality. From 1961 to 1998 humans increased at an average rate of 1.8 percent per year, but cattle increased at only 1 percent per year. The FAO-estimated 0.9 percent rise of protein added to the 1.8 percent increase of people means protein production rose fully 2.7 percent per year, outpacing cattle populations.

Equally surprising, pasture, which might have been thought to expand enough to support the extra protein production, expanded at a rate of only 0.2 percent per year. In an identity connecting population and other factors to pasture, the ratio of protein in the food supply to pasture area had to fall 2.5 percent per year. Although more animals eating feed rather than grazing lay behind some of this finding, the principal explanation must be more productive pastures and animals plus less animal product lost before it reached the table.

Forestland

Humans harvest trees for lumber for construction, pulp for paper, and wood for fuel. They clear forests for crops and pastures. Thus the expectation that rising population will shrink forests comes easily. But, contrary to that expectation, whereas forests shrank in some places, especially Africa, they expanded in Europe and the United States. French forests, for example, began expanding in the nineteenth century despite a French population that kept growing, although relatively slowly. Geographers have labeled the change from a negative to a positive connection between population and forests (from growing population and shrinking forests to expanding forests despite growing population), the forest transition. The annual 0.2 percent shrinkage of the world forest during the 1990s was made up of disparate trends, such as a 0.8 percent shrinkage in Africa but a 0.1 to 0.2 percent expansion in Europe and the United States.

Forests can be converted to farming. Whereas global forests were shrinking by 9 million hectares per year during the 1990s, pasture was expanding only about by 2 million hectares per year and cropland by less than 1 million hectare. Thus a balance of some 6 million hectares must have gone to the residual area–neither forest, cropland, nor permanent pasture–that comprises about a third of global land. Decreasing the encroachment of crops and pasture on forest further, agricultural uses can be subtracted from the residual area, and–with soil improvement and irrigation–even on formerly barren land. Expanding agricultural use by 1 hectare need not shrink forest area by 1 hectare.

Worldwide, foresters annually harvest about 0.4 percent of the 386 billion cubic meter volume of wood standing, calling the harvest "industrial roundwood." Much fuelwood fails to appear in such statistics. Because trees grow, harvesting is not a permanent subtraction from the forest. In the timberland of the United States in 1991, for example, forests grew by 2 cubic meters per hectare, exceeding the harvest by a third. Substitutes such as coal for fuelwood, concrete for poles, electronic documents for paper, and chipboard for planks, plus more efficient mills, steadily lessened the role of timber products in the U.S. economy.

High-yielding trees can spare natural habitat. Plantation trees can grow up to 20 cubic meters per hectare per year, producing the same harvest from 1 hectare as 10 hectares of the average U.S. forest. South Africa has only 4 percent of African land and 1 to 2 percent of its forest cover, but it has 19 percent of all African plantations and in 1994 cut fully 26 percent of industrial roundwood harvested on the continent. The forest area of South Africa scarcely changed from 1990 to 2000, whereas the forest of the entire continent of Africa shrank 0.8 percent annually. Intensive management can lessen the extent of logging use on natural lands.

The Residuum

After subtracting agricultural and forest land from the global supply, a residuum remains. Urban uses, mines, and oil wells occupy a few percent of it, but people leave much dry, infertile, or cold land unused. With effort, irrigation, and fertilizer, people can put some of this residuum to use.

Conclusion

Land use means land use by people. Therefore, population is the first determinant of land use, followed by the income of the population, which multiplies capability per person. Generally, however, the consumption of food and other products of land (from space for foundations to wood for fuel) does not rise in proportion to income, meaning consumption grows more slowly than population multiplied by income. Substitutes such as electronic messages for paper messages and gas fuel for wood fuel are one reason. Other technological developments such as skyscrapers and high-yield grain or trees add further leverage to modify a simple projection of land use in step with population.