Floristic Heritage

Plant Geography

denali landscape in fallAlaska lies at the edge of the continent Asia and North America. During the past two million years this area has been more closely associated with the biota of northeastern Asia as opposed to that of North America. This is because the periodic formation of continental ice sheets thousands of meters thick (which covered most of Canada and parts of the northern continental U.S.), has periodically separated Alaska from continental North America.

At the same time, the exposure of the Bering Land Bridge allowed plants and animals a wide terrestrial dispersal corridor into Alaska from northern Asia. For this reason, many of the plant species of Denali occur in Alaska and northern Asia, but not elsewhere in North America. These plants are known as Beringian endemic species – species that occur only within the large region that was mostly free of ice during the Pleistocene glacial advances.

Ecological History

The ecological history of the Denali region during the past two million years is characterized by repeated advances and subsequent retreats of massive sheets of glacial ice throughout the Pleistocene Epoch.  These repeated and enormous ecological upheavals have had profound influences on the nature of the biota resident in the Park and the very shape of the Park landscape itself.  In fact, at least half of the Park was intermittently covered by the Cordilleran Ice Sheet during glacial maxima!

alaska range in springAs a result of the formation of the Cordilleran Ice Sheet, only the areas well north of the Alaska Range proper were habitable during the periods of maximum glacial advance.  Holocene sediments within the Park show that the northern lowlands were dominated by dwarf birch low scrub tundra types (similar to what occurs in the subalpine and lower alpine regions of the Park currently), and that coniferous forest have only established in these areas in the last 6,500 years.

denali landscape with spruce treesThe fossil evidence from interior Alaska indicates that the Pleistocene epoch has seen repeated major shifts in the vegetation patterns on the landscape, which correlate with the advance and retreat of glaciers in response to major shifts in climate (specifically temperature and precipitation).  It is this dynamic of change that has profoundly shaped the composition of the endemic flora of this region.

Plants whose evolutionary histories are confined to Beringia are disproportionately plants of dry and open areas of the landscape including tundra, rubble slopes and dry meadow areas devoid of trees.  Conversely, few of Alaska’s endemic plant species occur in forested habitats.