TO AN AIR TRAVELER, the equatorial African rain forest looks like a thick, green carpet that stretches to the horizon and beyond. This illusion is interrupted only by occasional roads, rivers, lakes, swamps, patches of intercalary savanna, and clearings for villages and fields. When viewed from the ground, however, the apparent monotony resolves itself into a spectrum of astonishing diversity. The rain forest is home to over 7000 species of flowering plants, and they intermingle promiscuously. More than a hundred species of trees have been identified in a single sample plot the size of three football fields. With so many species competing for space, the floral composition of the forest varies widely from place to place according to altitude, rainfall, slope, ground water, soils, and other factors. The resulting patches, each subtly different from the next, form a mosaic that covers an area roughly the size of continental western Europe.

Human populations inhabit all regions of the rain forest, but they are spread thinly over the land. The estimated population density is less than four inhabitants per square kilometer, and it was roughly the same a century ago. The forest dwellers have nevertheless left their mark on the environment they inhabit. As Paul W. Richards has observed: