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THE SALIX SYRTICOLA DUNE ASSOCIATION 



In the southern part of the region occur the low fringing dunes 

 which are tenanted by the willow, Saliv syrticola. They are low flat 

 dunes, just a little out of the reach of the winter storms. They tend 

 to grow in width rather than in hight, and consequently this associa- 

 tion is one of the first to make a permanent vegetation on the beach. 



The plant itself grows as a straggly bush, sufficiently dense, ap- 

 parently, to cover the ground with vegetation but not to prevent a 

 strong wind from carrying away sand that may ha.\'e accumulated 

 at the bases of the stems. Because of this the hight of these dunes 

 depends upon the amount of protection that they have from the west- 

 erly winds. From Waukegan to the area of the pines, where there 

 is no such protection, the Sali.v syrticola dunes are from two to four 

 decimeters in hight. When protection is afforded by the pines the 

 dune will keep pace with the blowing sand to a hight of about three 

 meters. Only a few plants of this willow, however, are able to con- 

 tinue their growth upward with the accumulating sand, and the ridge 

 is broken up into a dune-complex in which only a few of tlie dunes 

 belong to this association. 



At the southern end of the area, where the beach is low and very 

 level, seeds of this willow germinate in the Juncus balticus littoralis 

 association. The plants are larger in the PotentiUa association, and 

 reach their average development in size on the low ridge just back 

 from it. This ridge is the typically developed Salix syrticola dune. 

 In this part of the region occur the majority of the secondary species, 

 virtually all of which are relics or invaders. 



A little farther north where the beach is still level, although 

 sloping upward all the way from the lake, the Salix syrticola dune, 

 composed of the dominant species only, occupies the lakeward front. 

 There is more blowing sand there and each plant is partly buried. 

 The plants continue their advance lakeward as fast as they are per- 

 mitted by means of their underground stems. 



EIST OE THE SPECIES OE THE SALIX SYRTICOEA DUNE ASSOCIATION 



Dominant Species ; 



Sali.v syrticola '^' 



Secondary Species 



Blymus canadensis Lathy nis iiiaritiimis (rare) 



Salix longifolia Salix glaiicophylla 

 Popuhis deltoidcs (i m. high) 



