Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 207 



the transition belt between the eastern humid chmatic conditions 

 and the western arid or semi-arid cHmate that characterizes the 

 great plains between the one hundredth meridian and the foothills 

 of the Rocky Mountains. There can be little doubt that the summa- 

 tion of semi-arid or arid characteristics that are revealed within this 

 region have exerted a very powerful influence upon the maintenance 

 of the general vegetation characteristics of the sandhills for untold 

 years essentially as we find them to-day. 



The normal precipitation in Nebraska varies from about 36 

 inches in the southeastern corner to 15 or 16 inches toward the 

 extreme western end of the state. This is through an interval of 



Fig. 6. Rainfall map of Nebraska. The figures show the normal rainfall in inches. 

 (Adapted from Briggs and Shantz.) 



more than four hundred miles. Briggs (19) and Belz have made 

 an extensive study of dry farming in the United States as related 

 to rainfall and evaporation. Figure 6, which I have adapted from 

 these investigations, portrays at a glance the above precipitation 

 wave as it sweeps from east to west across the state. These figures 

 which have been compiled from the records of the United States 

 Weather Bureau show that the rainfall for the sandhills varies from 

 about 23 inches on the eastern border to about 16 inches near the 

 western limits through a distance of about three hundred miles. 

 The intermediate position between relatively humid and arid con- 

 ditions is thus very clearly indicated. The normal precipitation at 

 various stations within or near the sandhills is shown in the fol- 

 lowing table which has been extracted from the extensive precipita- 

 tion table for Nebraska published by Briggs and Belz ( 19) . 



