FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 19 



presumably would indicate some form of Arctic or Alpine Life 

 Zone. So far as latitude is concerned, the southernmost island of 

 the Aleutian chain, Amatignak, lies not far north of 51° N., 

 which is the latitude of heavily timbered, coastal British Columbia 

 in the vicinity of Vancouver Island ; however, the treeless Aleu- 

 tians lie hundreds of miles south of the tree limit in the Brooks 

 Range of interior Alaska. Some of the lowest temperatures in 

 Alaska are recorded from the timbered interior, while the 

 temperatures in the Aleutians are uniformly higher in winter, 

 and the adjacent seas are not frozen over. From the standpoint 

 of vegetation growth, summer temperatures are probably of 

 greater significance than winter temperatures, and probably do 

 not show so great a variation. Certainly the temperatures aver- 

 age much lower and have a lower maximum in summer than 

 temperatures found in the forested continental areas. 



Wind is another factor that generally accompanies treelessness 

 at high altitudes and latitudes. There is a treeless coastal strip 

 bordering the Bering Sea, with few interruptions, from Alaska 

 Peninsula to Bering Strait, continuing around to the treeless 

 Arctic coast. This coastal area is characterized by strong winds, 

 as contrasted with the comparative stillness of the interior. We 

 know the effect of wind on tree growth at timberline in moun- 

 tains. In the Aleutians, I found many instances where the wind 

 had scoured out the soil, exposing the roots of such ground- 

 hugging plants as crowberry and dwarf willow. If wind is one 

 of the factors that establish the edge of forests, it is operative to 

 an unusual degree in the Aleutians. 



Forest growth is another important factor to be considered in 

 the Aleutian district. Attention is invited to the series of pub- 

 lications on Alaskan flora by Robert F. Griggs (see bibliog- 

 raphy) — particularly his 1934 report on the edge of the forest, 

 in which he has assembled numerous data to show that the edge 

 of the forest has been advancing in Alaska. This was particu- 

 larly evident on Kodiak Island and in the Katmai region, where 

 Dr. Griggs worked intensively. According to Griggs' studies, we 

 may reason that, since the last glaciation, climate or a combina- 

 tion of other factors has been gradually improving the area 

 toward suitability for forest growth. The forest, however, has 

 not been able to migrate fast enough to keep pace with favorable 

 climatic conditions and has not reached its potential limit. 



Where, then, is the limit of the potential climax forest growth? 

 At the end of the Alaska Peninsula? Farther west? On Mer- 

 riam's life zone map, the Hudsonian Zone is shown extending the 



