SUMMAEY. 23 



of young trees, and may even drive back and destroy adjacent forest. 

 As long as the burning continues the grasses remain, but with the 

 cessation of fires the forest growth is renewed. Such processes of 

 alternating denudations and reforestations have evidently continued 

 in Central America for long periods of time. 



It becomes evident that the simple operations of primitive agri- 

 culture, the mere cutting and burning of the natural vegetation, can 

 induce desert conditions, even in naturally forested tropical regions. 

 Though the effects of human activities may not be so direct or so 

 obvious in temperate climates as in tropical countries, it is well 

 to be aware of the fact that natural conditions can be profoundly 

 altered by human agencies. 



Apart from dangers of war or pestilence to which the ancient 

 communities of Central America may have been exposed, their exist- 

 ence was definitely limited by methods of agriculture which denuded 

 the country of its forests and destroyed the fertility of the soil. 

 Civilization is at an end when an agricultural country ceases to be 

 adapted to agriculture. To recognize these natural limitations of 

 the primitive civilizations of Central America should make us more 

 careful to appreciate and to correct the harmful tendencies of some of 

 our own systems of agriculture. 



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