Patterns of Terrestrial Vertebrate Diversity in New World Temperate Rainforests

Abstract

Temperate rainforests occur on the western margins of North and South America between approximately 40°-60°N-S latitude. These occur primarily in the Pacific Northwest region of the United States and Canada and in southern Chile, with extensions into neighboring precordilleran Argentina. The climate of these regions is characterized by high, predominantly winter precipitation as rain and/or snow, averaging 1500 mm to 3000 mm or more annually, and mild maritime conditions. Depending on whether the forests are perhumid or seasonal, summers may also be wet, or relatively dry, but not hot. In both hemispheres, volcanism, orogenic uplifts, and periodic Pleistocene glaciations have played a major role in shaping the modern landscape. The southern temperate forest region has also been affected by marine transgressions, particularly in the early and mid-Cenozoic. Today, the temperate forests of both regions are essentially isolated from coterminous regions by high mountain ranges (the Cascades and Rocky Mountains, for North America, and the Andes, for South America) that produce significant rainshadows to the east and, at the same time, ameliorate conditions to the west. As recently as the Pliocene, the southern temperate forests were much more extensive than at present, extending east through much of what is now semiarid Patagonian steppes.