ioo The National Geographic Magazine 



Photo from the Biological Survey 

 PRAIRIE DOGS AT MOUTH OP BURROW 



LIFP AND CROP ZONES 



It has long been recognized that plants 

 and animals are not distributed fortui- 

 tously over the earth, but in their distribu- 

 tion are governed by well-defined laws. 

 Certain species and groups of species are 

 restricted to certain regions because of 

 peculiarities of climate, temperature, and 

 soil, summed up under the word environ- 

 ment, essential to their well being. 



Cultivated plants are wild plants 

 tamed — wild plants modified to some ex- 

 tent by care and cultivation — but in their 

 nature and all essentials akin to their un- 

 cultivated ancestors. To a great extent, 

 then, the laws of distribution that apply 

 to wild plants and animals apply equally 

 well to cultivated varieties. The ready 

 application of these facts will appear from 

 an example. If on a certain mountain 

 side a particular crop is found to thrive, 

 and the observer happens to know the 

 particular plants, birds, and mammals 

 natural to the locality, when he visits a 



different region where the same plants 

 and animals find a congenial home' he 

 may be sure that the crop in question 

 will thrive there also. 



Such being the case, it was early per- 

 ceived that a study of the distribution of 

 wild plants and animals and the mapping 

 of the natural areas of distribution could 

 be made to serve a practical use, whereby 

 the farmer would be saved enormous ex- 

 pense in experiments to ascertain the par- 

 ticular crops adapted to new localities. 

 Accordingly, in the summer of 1889 Mer- 

 riam selected the San Francisco mountain 

 region of Arizona for an experimental 

 survey, and it is not too much to say that 

 the results of the work there revolution- 

 ized prevailing conceptions of the princi- 

 ples of geographic distribution. 



In ascending the mountain a succession 

 of climatic belts were traversed, similar 

 to the ones to be noted in traveling from 

 our southern boundaries to the Arctic, 

 each zone or belt being characterized by 

 a distinct set of animals and plants. 



