340 



THE JUNCUS TORREYI ASSOCIATION 



This small association, composed virtually of only the dominant 

 species, occupies very definitely the tension line between the blazing 

 star (Liafris spicata) and the Liatris scariosa associations. It may 

 extend slightly into both of them, but in such cases is evidently act- 

 ing as an invader in one and a relic in the other. This depends upon 

 which Liatris association is succeeding the other, since that succes- 

 sion is reversible and bears a seemingly definite relation to elevation 

 or depression of the water-table. The large dark green to brown 

 heads of the dominant species make this association stand out very 

 distinctl}^ from each of its neighbors. The usual width of the asso- 

 ciation is five to twenty-five centimeters, though it may be greater 

 or less according to the slope of the land. In blowouts where neither 

 Liatris is present, this Juncus occupies very definitely the median 

 position between the sets of plants which represent those two associa- 

 tions. 



I.IST OF THE SPECIES OE THE JUNCUS TORREYI ASSOCIATION 



Dominant Species 

 Junciis torreyi 



Relic or Invading Species (depending on the direction of succession) 

 Rynchospora capillacea Icviseta Stcironcma quadrifionim 



The Thicket Associations 



THE POPUEUS-SALIX-CORNUS THICKET ASSOCIATION 



This association is one of the usual steps in the succession from 

 marsh to oak forest. It is quite general in its distribution through- 

 out the central part of the Beach area. It may invade almost any as- 

 sociation, but it is most successful in the Liatris spicata, Calaiuagros- 

 tis canadensis, Iris versicolor, and blowout associations. 



Physical and Ecological Characteristics. — This association grows 

 in soil varying from sandy loam to the black soil of the prairie. The 

 water supply is always ample on account of the proximity of the 

 water-table level of Lake Michigan. The growth of the thickets is 

 very dense, and in the protection thus afforded considerable humus 

 may be formed. 



The Association. — The association is composed of any one of 

 the dominant species or of different combinations of them. Dogwood 

 (Cornus stolonifera) and the species of willow (Sali.v) are each 

 much more abundant than the species of Populus. There seems to 



