Flora and Vegetation

South America’s shape, size, and geographic position, now and in the past, have acted to influence the development of diverse coverings of land surfaces with plants of different sizes, adaptations, and origins. Underlying geologic structures have been exposed to weathering regimes, thereby resulting in a multiplicity of landforms, soil types, and ecological zones. The most notable large-scale features are the Andes, which curl along the western margin of the continent, and the broad swath of the Amazon lowlands in the equatorial zone. However, there are also extensive, more ancient mountain systems in the Brazilian Shield of east-central Brazil and the Guiana Shield in northern South America. The interplay of environmental factors has given rise to a panoply of vegetation types, from coastal mangroves to interior swamplands, savannas, and other grasslands, deserts, shrublands, and a wide array of dry to moist and lowland to highland forest types. The narrower southern half of South America is also complex vegetationally because of the compression of more vegetation types into a smaller area and the diverse climatic regimes associated with subtropical and temperate middle latitudes. Alexander von Humboldt began to outline the major features of the physical geography of South America in his extensive writings that followed his travels in the early nineteenth century (von Humboldt, 1815–1832). For example, he first documented the profound influences of contemporary and historical geologic processes such as earthquakes and volcanoes, how vegetation in mountainous areas changes as elevation influences the distributions of plant species, and the effect of sea surface temperatures on atmospheric circulation and uplift and their impacts on precipitation and air temperatures (Botting, 1973; Faak and Biermann, 1986). His initial insights, in combination with modern observations (Hueck and Seibert, 1972; Cabrera and Willink, 1973; Davis et al., 1997; Lentz, 2000), still serve to frame our synthesis of the major vegetation formations of South America. In this chapter, we relate vegetation formations to spatial gradients of soil moisture and elevation in the context of broad climatic and topographic patterns.