478 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



in every month. Note that I said helow zero^ not merely below freez- 

 ing. But, while summer temperatures average dangerously close to 

 freezing, winter averages are milder than one might expect, and there 

 obviously cannot be many — 56's coming along to allow such a relatively 

 mild January mean of —17° F. Nonetheless, even a single —56° 

 cannot be ignored as a factor in the destiny of arctic plants. 



Barrow gets neither the most extreme nor the mildest temperatures 

 of the Arctic, but on the average it is reasonably typical. Despite 

 increasing latitude, average temperatures are remarkably uniform 

 throughout the Arctic, owing largely to the ameliorating effects on all 

 sides of the polar sea. The average temperature for the warmest 

 month is commonly between 40° F. and 50° F,, and in fact the 50° F. 

 isotherm is often taken as the climatological southern limit of the 

 Arctic. 



Temperature is an extremely capricious variable anywhere in the 

 arctic-alpine environment, and its effects are not all measured by means 

 and long-term extremes. Drastic short-term or sustained fluctuations 

 during the critical growing period are common fare year in and year 

 out for arctic-alpine plants, which must be adapted to withstand 

 these hazards. In the Arctic of Alaska I have frequently seen the 

 temperature fluctuate 40° F. or more in less than 24 hours, going in one 

 case from near 80° F. down to very near freezing. Porsild (1951) 

 recounts a fascinating experience he had east of Great Bear Lake, 

 northern Canada, one April, watching the frost play with a clump 

 of Richardson's willow {Salix richardsonii Hook.). During a brief 

 thaw the buds swelled to the point where the catkins were ready to 

 expand, even while the basal parts of the clump were buried in 3 

 feet of ice and snow. Then, abruptly, freezing temperatures set in 

 for another 3 weeks, and the buds froze solid. When the final thaw 

 came, thoy began where they had quit and went on quickly to flower and 

 produce seed, apj)arently unaffected by the frigid interlude. He tells 

 also of one July night in the Yukon when he saw the large purple 

 flowers of Epilohiwrn latifoliuTn L. freeze solid like wax flowers, only 

 to thaw out again next day looking no worse for having frozen. One 

 need not reflect long on his own experience to realize that these are 

 not ordinary tolerances. 



Along the Arctic coast fog and cloud cover are significant factors 

 in regulating surface temperatures during the growing season, and 

 they can be responsible for very rapid fluctuations. As anyone knows 

 who has ever been to Barrow, for example, the skies can be bright and 

 sunny one moment and almost the next be blanked out by a "soupy" 

 fog. In a land of frozen ground, where the surface holds little residual 

 heat, temperatures spiral downward rather dramatically sometimes 

 when the skies become even partially overcast. 



