NORTHERN LIMITS OF EAST CANADIAN TREES IN 

 RELATION TO THE CLIMATE. 



By H. R. Christie. 



Mayr based his division of forest regions on climate. Tem- 

 perature, precipitation and humidity are the most important 

 climatic features. The average temperature of the tetrahore (i. 

 e. the four growing months) is the most important factor in de- 

 termining the distribution and extension of species in the north- 

 ern hemisphere. 



According to Mayr forest cannot exist if, during the tetrahore, 

 the average temperature is below 50° F; precipitation is less than 

 1.95 inches; average humidity is below 50° and at the same time 

 precipitation less than 3.9, say 4 inches. 



If precipitation exceed 4 inches, a forest will exist even 

 though the air be dry. 



The problem was to ascertain what relation, if any, exists be- 

 tween the climate of the tetrahore and the northern limits of 

 Canadian trees of the Atlantic flora. 



The desired data were obtained from "Canadian Monthly 

 Weather Review", and "Canada's Fertile Northland", through the 

 courtesy of R. S. Stupart, Director of Meteorological Station, 

 Toronto. 



A number of representative stations distributed as evenly as 

 possible along the different parallels of latitude were selected. 

 For these points the tetrahoral average temperatures, as Avell as 

 the total precipitation for the tetrahore, were determined. 

 Humidity was given for so few stations (ranging from 57° to 

 80-I-) that it was neglected. Where the average temperature of 

 any month fell below 40°, it was excluded, and the average tem- 

 perature at such points stated on the map includes only the 

 months of June, July and August. 



Examination of the tables shows that precipitation at practi- 

 cally every station is abundantly sufficient for supporting forest 

 growth, being well above Mayr's 4 inch limit. We may, there- 

 fore, say that the deciding climatic factor in Canada (exclusive 

 of British Columbia and prairie) is temperature. 



