Pollen sequence from late quaternary sediments in yellowstone park.

A radiocarbon-dated pollen diagram from a depression near the end of the southeast arm of Yellowstone Lake, Wyoming, records the vegetation sequence from the retreat of Late Wisconsin (Pinedale) ice to the present time. The tundra Picea-Abies-Pinus albicaulis (spruce-fir-whitebark pine) parkland vegetation inferred during late glacial time changed rapidly to a Pinus contorta (lodgepole pine) forest shortly before 11,550 carbon-14 years ago, suggesting a warming trend at that time. The Pinus contorta forest persisted with minor modification throughout postglacial time.