PLANTS IN ARCTIC-ALPINE EN\r[RONMENT — SHETLER 483 



primary significance of glaciation lies in its historical role in shaping 

 the Arctic as we now know it. Most of the present-day Arctic is 

 simply too arid and flat for large accumulations of ice. There are, 

 however, scattered montane glaciers of local significance in the Low 

 Arctic. Nonetheless, one is conscious of the recent geological past in 

 this youthful land where in many instances primary ecological suc- 

 cession has only just begun since the retreat of Pleistocene ice. In 

 the Alpine, on the contrary, glaciers and glaciation are still a present 

 factor in the environment. This is particularly evident in subarctic 

 Alaska, where receding glaciers annually continue to bare new land 

 surfaces and moraines for plants to colonize (pi. 7, fig. 1) . 



Snow and snow^ accumulations fer se are considerably more im- 

 portant in the Alpine than in the Arctic, at least the nonmontane 

 parts of it. Annual snowfall is usually much heavier, to be measured 

 in feet not inches, and this makes not only for a deeper accumulation, 

 hence later thawing, but also for much greater mechanical hazards. 

 Heavy deposits may crush woody plants, especially at timberline, 

 and violent snowslides may sweep whole slopes clean of vegetation 

 in one swift moment, not just once, perhaps, but again and again. 

 Frequent snowslides apparently accomit for some large open areas 

 at timberline that might otherwise have been overgrown with trees 

 (pL6,fig.l). 



Flooding can be an important influence in the development of vege- 

 tation both in the Arctic and the Alpine, but particularly the former. 

 Annual spring thaws send torrents of meltwater rushing down 

 gulches and ravines, which in the Arctic feed large rivers that flood 

 the tundra slopes and plains, sometimes altering the landscape mark- 

 edly. During unusually rainy summers, as our party experienced 

 in the Alaskan Arctic in 1963, flooding may be prolonged and re- 

 peated. Wliile camped along the lower reaches of the Noatak River 

 (northwestern Alaska) in late June and early July, in less than a 

 week we watched that mighty river rise ominously to a flood stage 

 of more than 5 feet above normal. Virtually every flat and gulch 

 along the river was inundated, as the water backed far up into the 

 tributaries. Many willows, legumes, and other plants in full flower 

 became partially or wholly submerged by the icy water not many 

 degrees above freezing and remained submerged for several days 

 to nearly a week before the flood completely subsided. One small 

 patch of mountain avens {Dryas integrifolia M. Vahl; very similar 

 to other species in pi. 9) stood completely buried in about 6 inches 

 of clear cold water for nearly a week without showing any apparent 

 damage; all the while its big white flowers looked as fresh as ever. 

 It was as though they and many other flowers had been put in the 

 refrigerator for a week to prolong their life, and outside of a little 



