Plant fossils, such as leaves, wood, cones, pollen, and seeds, provide important evidence of how Alaska's vegetation has responded to climate changes over time periods of centuries to millions of years.
USGS studies of the Alaskan fossil record of plants include data from many natural exposures and sediment cores (fig. Global cooling began about 14.5 Ma, and its influence on Alaskan vegetation was abrupt and dramatic.
Global climate changes during the past 2.5 million years have been extreme, oscillating between relatively long periods (ca. During warm interglacial periods such the one we are currently experiencing (the Holocene, spanning the past 10,000 years), boreal forests of spruce, larch, poplar, birch, alder, and willow spread throughout most of interior Alaska.


During periods of less extreme cool climates (interstadials), Alaskan vegetation was dominated by shrub and herb-shrub tundra communities; boreal forest vegetation was restricted to a few areas in the interior lowlands of Alaska. The study of past climates and ecological changes in Alaska are an important key to understanding the likely consequences of future climate changes in high latitude ecosystems.
Temperate trees disappeared, leaving behind a simpler forest vegetation of hardy birch, alder, and pine species until a more complex conifer-dominated forest developed after about 12 Ma. These data provide the basis for reconstructing the record of past vegetation changes over millions of years of Earth history. The fossil record shows that dramatic changes in high latitude vegetation have occurred many times in the past, primarily in response to global climate changes.


Geological Survey's global change drilling project at Fort Yukon, Alaska recovered a detailed record of climate and environmental change for interior Alaska spanning much of the past 16 million years. The record further suggests that the magnitude of ecological response to global climate change is greater at high latitudes than at low latitudes.



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