THE ART OF THE SECOND GROWTH 



Sumac, Sassafras, Locust, etc. These species act as ushers for 

 more exacting forest growth, improving the physical conditions of 

 the soil. Little is known about the nature of the improvement. 



Paragraph IV. The North American sylva. 



The northern limit of the forest coincides with the isothermal 

 line of 30 degrees Faht., which lies on the west side of the continent 

 at Co degrees latitude in Alaska (under influence of the Japan cur- 

 rent), and on the east side at 57 degrees latitude in Labrador and 

 at the Hudson Bay. 



The tropical forest shows no seasons. Its species are evergreen. 

 In the United States it is found at the extreme southern point of 

 Florida and of Texas. 



The sub-tropical forest is characterized by the evergreen broad- 

 leaved trees, and is the zone of rice and oranges, extending in east- 

 ern North America to 35 degrees, in western North America to 40 

 degrees, latitude. 



The moderately warm forest region is the zone of the broad- 

 leaved deciduous trees, of corn, vine and wheat. 



The moderately cold forest region is that too cold for the 

 production of corn. 



In North Carolina a trip from the coast to the high Balsams 

 leads the traveler from the northernmost limit of the sub-tropical 

 through the moderately warm forest region into the southernmost 

 limit of the moderately cold forest region which sets in at about 

 4,000 feet elevation. 



The following table shows the composition of the forest of the 

 United States and of Canada, under the influence of the climate: 



Percentage of forest area occupied by: 



In United States. In Canada. 



Tropical forest i^% 0% 



Sub-tropical forest 15 % 0% 



Forest of the moderately warm zone 75 % 10% 



Forest of the moderately cold and alpine zone... 9V2% 90% 



The United States contain two big and one minor forest region, 

 namely the 



Atlantic forest region; 

 North Mexican forest region; 

 Pacific forest region, 



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