284 cook: vegetation in southern peru 



BOTANY. — Agriculture and native vegetation in Peru. 0. F. 

 Cook, Bureau of Plant Industry. 



Alternation of forests with open grass lands or sparse desert 

 vegetation is one of the most striking of the biological phenomena 

 of tropical countries. Since the time of Humboldt many travelers 

 in tropical America have sought to explain the presence or absence 

 of the different types of vegetation by reference to differences 

 of geological formations, altitudes, prevailing winds, or other 

 natural features. More recent observations in Central America 

 have led to the opinion that the chief factors governing the 

 distribution of the forest vegetation are the agricultural occupa- 

 tion of the land and the continued action of fire on lands aban- 

 doned from cultivation. 



There are reasons for believing that most of the forests of Central 

 America do not represent original or virgin growth, but different 

 stages of reforestation. Likewise most of the open grass lands 

 and deserts appear to be consequences of the native system 

 of farming — to be interpreted as artificial conditions rather than 

 as natural features. The climatic, geologic, or topographic 

 factors, though not without influence in determining the rate 

 of reforestation, seem in general to have very little importance 

 in comparison with human activities and exposure to fire. The 

 complete reforestation of fireswept grass lands is a long and 

 gradual process, but the successive stages can be recognized 

 by taking account of the habits of the different kinds of trees. 1 



Opportunities of studying the relations of agriculture to forest 

 vegetation under a different combination of natural conditions 

 have been afforded during four months (April to July, 1915) 

 spent in southern Peru and Bolivia as a member of the Expedi- 

 tion conducted by Professor Hiram Bingham, under the aus- 

 pices of Yale University and the National Geographic Society, 

 with the cooperation of the United States Department of Agri- 

 culture. Most of the time was spent in the region traversed 

 by the Urubamba River and its tributaries, from the Pass of 



1 Cook, O. F. Vegetation Affected by Agriculture in Central America. Bull. 

 145, Bureau of Plant Industry, U. S. Dept. of Agriculture. 1909. 



