Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 215 



especially noticeable in certain portions of Garden County where 

 the reflected light is so strong that early eye fatigue results and 

 studies are continued under disagreeable conditions unless one is 

 provided with stained glasses. 



The region as a whole is exposed to strong illumination. How- 

 ever it is only in connection with the woodland vegetation and pos- 

 sibly also with certain aquatic and helophilous associations that light 

 becomes an important limiting factor. 



Soil-moisture is the controlling factor in the distribution of the 

 lowland species and associations. Silting-in and chemical compo- 

 sition of the soil solution are additional conditions that aid in the 

 differentiation of the vegetation groups of the lowlands. 



Although there are at present numerous larger or smaller areas 

 in the sandhills where sand movement is extreme, it must be stated 

 that the region as a whole is effectively protected against wind 

 action by an efffcient grassy cover. The region is not a moving 

 dune landscape as some suppose ! The initial practice in dune 

 reclamation has therefore been consummated through the activity 

 of nature herself without the aid of man, but it appears that man 

 has done little to better the uplands after they have been so well 

 and thoroughly stabilized as a result of the interaction of natural 

 forces. Practical methods for the reclamation and utilization of 

 dune areas have been suggested by various investigators, especially 

 Hitchcock (41), Free and Westgate (35), Poisson (52), and Ger- 

 hardt {Z6). 



THE PLANT FORMATIONS 



I do not propose to enter here into a lengthy discussion of the 

 general concept or nature of plant formations and associations. 

 This has been done in a number of cases in the literature cited 

 herewith and the reader is referred to those papers for discussions 

 of this phase of phytoecology. The views of Clements (23, 24, 25), 

 Cowles (31), Moss (49), Tansley (65, 66), Jennings (43), and 

 Warming (71) upon plant formations have had the widest test and 

 application. 



There can be no question of the fact, as Moss (49) has pointed 

 out, that there has been too great a tendency in the past to elevate 

 minor vegetation units to the dignity of plant formations. Errors 

 of this sort may be readily accounted for in some cases from the 



