The American continent extends over 12,000 kilometres from Alaska to Cape Horn, and encompasses an enormous variety of environments from arctic to tropical. For the purposes of this discussion, such a huge variety has to be simplified into a few major geographical units within the three regions of North, Central, and South America (Fig. 7.1). Large tracts of Alaska and modern Canada north of the 58th parallel consist of tundra, which extends further south down the eastern coast of Labrador. To the south, boreal coniferous forests stretch eastwards from Lake Winnipeg and the Red River past the Great Lakes to the Atlantic, and westwards from the slopes of the Rockies to the Pacific. The vast prairies in between extend southwards through the central United States between the Mississippi valley and the Rockies, becoming less forested and more open as aridity increases further south. South of the Great Lakes the Appalachian mountains dominate the eastern United States, making a temperate landscape of parallel ranges and fertile valleys, with sub-tropical environments developing in the south-east. The two together are commonly referred to as the ‘eastern Woodlands’ in the archaeological literature. On the Pacific side are more mountain ranges such as the Sierra Nevada, separated from the Rockies by arid basins including the infamous Death Valley. These drylands extend southwards into the northern part of Central America, to what is now northern Mexico, a region of pronounced winter and summer seasonality in temperature, with dryland geology and geomorphology and xerophytic vegetation. The highlands of Central America, from Mexico to Nicaragua, are cool tropical environments with mixed deciduous and coniferous forests. The latter develop into oak-laurel-myrtle rainforest further south in Costa Rica and Panama. The lowlands on either side sustain a variety of tropical vegetation adapted to high temperatures and frost-free climates, including rainforest, deciduous woodland, savannah, and scrub. South America can be divided into a number of major environmental zones (Pearsall, 1992). The first is the Pacific littoral, which changes dramatically from tropical forest in Colombia and Ecuador to desert from northern Peru to central Chile. This coastal plain is transected by rivers flowing from the Andes, and in places patches of seasonal vegetation (lomas) are able to survive in rainless desert sustained by sea fog.
White Christmas? An Application of NOAA’s 1981–2010 Daily Normals
