Land, Water, and Forests
We abuse land because we regard it as a commodity
belonging to us. When we see land as a community
to which we belong we may begin to use it with love
-- Aldo Leopold, 1948
Among physical resources, land is central in importance. By land we mean not only physical space but also the characteristics that govern the uses to which land can be put. Those characteristics include the topography (the shape of the terrain--for example, flat, hilly, or mountainous), the quantity and quality of soil, the availability of water, and the nature of local climates. Of course, those features are interrelated, and together they influence and are influenced by the vegetation that grows on the land: soil is a product of the underlying rock, the climate, the topography, and the creatures living on it and in it; the availability of water depends on how much falls as rain and snow, on how much evaporates, and on how much is retained, where, and for how long; the latter properties depend on local soil and vegetation as much as they influence them.
Many of the basic physical principles underlying these relations am described in Chapter 2, Chapter 3, and Chapter 4. In this chapter we discuss the characteristics of Earth's land and its supplies of fresh water as resources--that is, in terms of their availability and suitability for the support of the human population. The closely related topics of forests and the production of timber are also treated here; production of food is the subject of Chapter 7.
Earth has a land area of 149 million square kilometers (58 million square miles), which in 1975 was occupied at an average density of about 27 people per square kilometer