PLANTS IN ARCTIC-ALPESrE ENVIRONMENT — SHETLER 485 



that the rosette habit is at least in part brought about by the arctic 

 type of light regime. 



In the Alpine the light regime is quite different in temperate regions. 

 Owing to the thinner high-altitude atmosphere, the light is both very 

 intense and high in ultraviolet rays. The days are not abnormally 

 long, of course, and the sun is more directly overhead. 



THE PLANTS 



Every time I step from a "bush" plane into a different part of the 

 Arctic or climb to the Alpine of a new mountain, I am impressed anew 

 with the basic uniformity of their habitats and vegetation. To the 

 biologist, botanist and zoologist alike, it has come to be axiomatic that 

 one encounters fewer and fewer species, which at the same time become 

 more and more widespread, as he moves from tropical to temperate 

 to polar regions or, on a smaller scale, from sea level to higher eleva- 

 tions. Thus, the botanist finds that the arctic-alpine flora is not nearly 

 so diverse and rich in species as temperate and tropical floras, and it 

 has a much smaller endemic element. Arctic-alpine species tend to 

 be circumpolar. This uniformity of the flora clearly reflects the 

 almost tedious uniformity of the environment, which is generally so 

 harsh and hostile to plants that only a small percentage of the earth's 

 flora has been able to invade it. Once successfully adapted, a species 

 is then able to spread throughout the peculiar arctic-alpine environ- 

 ment, and many species have done just that. 



In order that we might get a bird's-eye view of the plants in the 

 arctic-alpine environment, I will attempt in the ensuing discussion to 

 touch briefly on some ecological, morphological, floristic, taxonomic, 

 and geographic aspects. 



LIFE ZONES AND CLIMAX FORMATIONS 



The correlation of certain plants and animals with altitude on the 

 one hand and latitude on the other was first carefully examined by 

 C. Hart Merriam, who, as the result of a biological survey in the San 

 Francisco Mountains of Arizona in 1889, formulated his classic "Life 

 Zone" concept and certain climatic laws to explain it. He was able to 

 recognize rather distinct horizontal vegetation belts on the mountain 

 slopes, which graded from one into another with increasing altitude. 

 He postulated that this rather distinct zonation of the vegetation was 

 due to a climatic zonation, and he went on the generalize that this was 

 not a local phenomenon but that the same zones in the same unique 

 sequence occurred on all high mountains. Depending on the latitude, 

 the whole sequence was shifted up or down in altitude. Further, he 

 proposed that some of these zones had latitudinal counterparts. His 

 zones, from highest to lowest, were : Arctic- alpine, Hudsonian, Cana- 



720-018—64 33 



