CLIMATIC FACTORS 



95 



Livingston and Shreve (1921) have plotted the moisture-temperature 

 divisions of the United States from scanty data but with considerable 

 success. 



Ocean Currents and Wind. — The temperature of a land mass is 

 greatly influenced by ocean currents and winds. Currents like the 

 Gulf Stream, which flow poleward, bring water from warm seas and 

 transmit their heat to the overlying air. Ireland is indebted to the 

 Gulf Stream for her colonies of Mediterranean plants such as Arbutus 

 unedo and Ruhia peregrina and for her Tertiary relicts of mosses and 

 liverworts. This distribution is parafleled by the presence of A. 



273 



25'^ 

 223 



c 



• S 177 



C5./27 



|.3 





76 



51 



25 



Fig. 50. 



-11.9" -6.5'' -1° +^M" W 15.5° 21.1''26.70C 

 Mean annua/ -femperafure 

 -Climatic humidity based on precipitation influenced by temperature. 

 McDougall.) 



{After 



menziesii and Quercus garryana, members of the broad sclerophyll 

 forests of California, on Vancouver Island, due to the warm currents 

 of the Pacific. The Gulf Stream also makes possible the advance of 

 tender Atlantic species and communities as far north as western 

 Norway and the Faroe Islands (Fig. 51). Its "Atlantic waters," very 

 rich in plankton, at Iceland still have a temperature of 11° to 13°C. 



Cold ocean currents reduce the temperature of adjacent coastal 

 regions. The southwestern and northwestern coasts of Africa are 

 thus cooled, with corresponding effects upon vegetation. The east 

 Greenland current, poor in plankton, lowers the temperature of the sea 

 water by 1° to 5°C. 



