276 



Invading Species (of relatively frequent occurrence) 

 Jitncus balficiis litforalis 



Invading Species (of rather rare occurrence) 

 Sali.r lougifolia Panicum sp. 



Sali.v glaucophylla ArctostapJiylos nva-ursi 



Sali.v syrticola Pctalostcmuni purpureum 



THE JUNCUS BALTICTTS LITTORAUS ASSOCIATION 



One of the first indications of the first type of upper beach, d.)s 

 Cowles (1899:167 et seq.) terms that part of the beach which is en- 

 tirely without wa\'e action throughout the year, is the presence of the 

 rush Jiinciis bolticus litforalis. It grows from straight rhizomes 

 which may be over three meters in length. The lines of plants cross 

 and recross each other in every direction. Expansion on the land- 

 ward side is ecologically impossible because of the closed association 

 behind it. Progress out on to the middle beach is limited only by 

 the action of the waves in winter and by the winds which keep un- 

 covering the outermost rootstalks. As the lines grow outward the 

 shifting sand is retained around the bases of the plants. It may even 

 form embryonic dunes to the bight of a few centimeters. This work, 

 however, is nearly always destroyed when the westerly winter winds, 

 with nothing to impede them, carry the sand back into the lake. The 

 Jitncus itself does not seem to be able to fix the dunes, but it is a 

 pioneer that enables dune-fixing plants to gain a foothold on a low 

 and level beach like that which, in the southern part of this area, 

 extends from Beach to Waukegan. There is no Jitncus where the 

 slope of the shore is 15° or more. The lakeward side of this associa- 

 tion is composed of just the one species, Jitncus halticus littoralis. 

 In the middle and in the landward side other plants appear. The 

 most abundant of these is silverweed (Potcntilla anserina), of which 

 more will be said in connection wdth the following association. Small 

 straggling plants of SqUa- syrticola occur at intervals, but as a com- 

 ponent part of this association they are not well developed. Occa- 

 sionally a dwarfed, small-leaved plant of Cottonwood, Populus dd- 

 toides, may be seen. Because of the deficiency of nutriment in the 

 soil the cottonwoods grow very slowly — sometimes not more than a 

 couple of centimeters in a season. Scirpiis anicricanits occurs here 

 more frequently than in the Triglochin palitstris association, but still 

 is not abundant. It has a remarkable tendency to grow in a spiral 

 form when it grows in the sand. 



