287 



THE POPULUS CANDICANS DUNE ASSOCIATION 



In a restricted area between Beach and Zion City occnr the dunes 

 of maximum hight. They are surmounted by narrow groves of bahn 

 of Gilead {Fopidus candicans). The tree trunks show no evidence 

 of being buried. On the other hand, at the ends of the association 

 there is every evidence to show that sand is being blown lakeward, 

 and, to a shght degree, landward, upon an adjoining prairie or heath, 

 as the case may be. 



Populus candicans is a plant which facilitates the growth of dunes 

 but it does not originate them. The plants of the dunes are all trees 

 of average size. The young plants, when present on dunes at all, oc- 

 cur among other species, especially with Pruniis pnmila. By far the 

 greater number of the young plants occur in the heath and the Liatris 

 scariosa associations. There they grow, and by their shade the den- 

 sity of the ground flora is reduced. As this disappears sand is set 

 free to the wiml, and may then form a ridge dune. These dunes are 

 quite similar to those found by Jennings (1909:338) on Presque Isle. 

 There, however, it is cottonwood {Populus dcltoidcs) that is the dune 

 nucleus. Populus deltoid es occurs in the Beach region along the mar- 

 gins of either permanent or temporary lagoons but the individuals 

 are separated and do not show a tendency to become dune- formers. 

 A Populus candicans dune is shown in the background of Figure 2, 

 Plate XLVIII. 



UST OF THE SPECIES OF THE POPULUS CANDICANS DUNE ASSOCIATION 



Dominant Species Secondary Species 



Populus candicans Prunus pnmila 



THE ELYMUS CANADENSIS DUNE ASSOCIATION 



Dunes of this type are infrequent and of little importance in this 

 region. They are low (3 dm.) with a rather steep front towards the 

 lake and a very gradual slope away from the lake. The crest is occu- 

 pied by wild rye (Elyinus canadensis) and the slope by that species 

 mixed in with Sporobolus cryptandrus and Artemisia caudata. West- 

 ward of these dunes is an open area from which sand has been re- 

 moved by man to the lake-level. The Blymus dunes keep the lake 

 from flooding the area and the spring rains from running directly 

 into the lake. 



