CHAPTER III. 



THE FOREST AS A CONDITION. 



The earth may be said to be a potential forest. 

 A cover of tree growth more or less dense is or has 

 been the natural condition at least of the larger 

 portion of the habitable earth ; and of the entire 

 land surface not less than 60 per cent may be 

 classed as actual or potential woodland. 



In the struggle for existence and for occupancy 

 of the soil between the different forms of vegeta- 

 tion, tree growth has an advantage in its perennial 

 nature and in its elevation above its competitors for 

 light, the most essential element of life for most 

 plants. These characteristics, together with its 

 remarkable recuperative powers, assure to the 

 arborescent flora final victory over its competi- 

 tors, except where climatic and soil conditions are 

 not adapted to it. 



The entire absence of tree growth from some 

 localities, such as the northern tundras and the 

 high peaks above timber line, is due both to tem- 

 perature and soil conditions. Here the two char- 

 acteristics of perennial life and persistent height 

 growth, become unfavorable, since extreme winter 

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