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The Migration of the Boreal Forest Over 21,000 Years

The Boreal forests sit in the extreme northern regions of the world and have migrated across the continents over the course of several millennia. During the same time period, the vegetation in the forests has also changed. NASA used paleoclimatological data gathered from everything from fossilized trees to ancient pollen grains to develop the maps featured above showing the migration of the boreal forests over the past 21,000 years.

The maps illustrate the movement of pine, spruce, birch, and non-grass prairie vegetation from 21,000 years ago to present.

Increasing color intensity represents increasing concentration of pollen, which is proportional to the amount of that species in a given area.

The Laurentide Ice Sheet is pale blue, and areas where no data were collected are white.

Spruce and northern pines began to retreat northward on the heels of the ice sheet 18,000 years ago. Nearly 15,000 years ago, the ice age’s dominant spruce species, P. critchfieldii, went extinct. By 12,000 years ago, the southern limit of remaining spruce and northern pines extended little farther than mid-continent, while their northern limit reached almost to Newfoundland, Canada. Fir and birch require more precipitation than spruce, and lagged the northward trek by several thousand years.

Between 12,000 and 9,000 years ago, spruce, fir, northern pines, and birch coexisted south of the edge of the glacier, which still covered much of Canada. Rapid increases in warmth during this period during the summer months caused spruce to decline, and northern pines dominated the early boreal forest.

Even as recently as 9,000 years ago, both spruce and birch, by that time well established in Canada and the northern United States, were still not settled into the present range, and actually began to spread southward once again. Around 6,000 years ago, the last of the continental ice sheets had melted, and the boreal forest was beginning to resemble its current self.