Northwestern North America

The mountainous terrain of northwestern North America currently supports a range of vegetation spanning coastal temperate rain forest to sagebrush steppe. Pollen records indicate a diverse set of ecological processes tracking a complex climate history. The region was divided by the Cordilleran ice sheet until close to the end of the Pleistocene. Abrupt climate changes during the deglacial led to rapid vegetation changes in northern areas, but vegetation in southern regions was less sensitive. Early Holocene vegetation indicated warmer and drier climates with more frequent fire from Oregon to central British Columbia, but in Alaska, conifer forest was slower to establish, indicating a complex climatic history. The late Holocene was marked by increased forest density and cool-adapted taxa in Oregon to British Columbia and increased black spruce peatland vegetation in Alaska.