Introduction to the Amazon

Abstract

Abstract There are various ways to define and delimit the Amazon in order to convey it as a natural, biogeographic region. Within Brazil it is sometimes defined as Amazonia Legal (Legal Amazon; see Mahar, 1989), but this is a political and economic entity that not only excludes the Amazon regions of adjacent countries, but also includes large areas of non-Amazon vegetation in the south. The watershed of the Amazon river and its tributaries is a better definition, but this excludes large areas of Amazon rain forest in the Guianas and Venezuela that are drained by other rivers, and again includes non-Amazon vegetation in the south. I have therefore followed the floristic criteria of Daly and Prance (1989) and defined the area, henceforth referred to as the Amazon region, as the extent of the lowland rain forest, roughly corresponding to Humboldt’s hylaea(a term that has come to mean the lowland rain forest, adapted by Humboldt from the Greek word hyle,meaning “forest”). This is a phytogeographic definition, and in the distribution maps used here the area is delimited by the dotted line. The western margin is the 500 m contour of the Andes, and the eastern margin is the Atlantic Ocean. As pointed out by Daly and Prance, however, the northern and southern limits of the lowland rain forest are difficult to define, for several reasons. All along the periphery of the region there are transitions to other vegetation types, and the boundaries between these are not always clear. In Colombia, I use the Rio Meta as northern boundary rather than the Rio Guaviare, in order to include the gallery forests of Vichada. Ducke and Black (1953) noted: “The only natural limits of Amazonia are the Atlantic and the Andes; on the north and south extremes the rain forest is gradually replaced by the flora of the neighboring countries.” The Amazon region thus includes, from the northeast, all of French Guiana, Surinam, and Guyana; southern Venezuela; southeastern Colombia; eastern Ecuador; eastern Peru; northeastern Bolivia; and all of northern Brazil (Figure 1.1). This is an enormous area of over 6.5 million km