274 



Invading Species 

 Scirpiis auiericaniis Triglochin paliistris 



THE TRIGLOCHIN PALUSTRIS ASSOCIATION 



This association is present every year. It normally occurs along 

 the margins of the beach pools or in moist sand in other depressions. 

 The individual plants of the Triglochin, which comprise about 70 

 per cent, of the area, grow close together in small tufts. The tufts 

 themselves are separated by intervals of two to three to ten centime- 

 ters. Toward the landward side, where the tufts are still farther 

 apart, the secondary species of this association occur. They are pi- 

 oneers of succeeding associations, the most important of which is the 

 Juncus balticus Uttoralis, which grows in higher ground than does 

 the Triglochin. 



LIST OF THE SPECIES OF THE TRIGLOCHIN PALUSTRIS ASSOCIATION 



Dominant Species Relic Species 



Triglochin palustris Juncus alpinus insignis 



Invading Species 



Juncus balticus Uttoralis Juncus torrcyi 



Potentilla anscrina Scirpus aniericanus 



Populus deltoid cs (a few small Cy perns rivularis 

 seedlings under 12 cm. higli) 



THE CARKX OEDEKI PUMILA - CYPERUS RIVULARIS ASSOCIATION 



This association occupies a still higher position on the l)each than 

 the preceding one. It occurs around beach pools, but is more likely 

 to be found in swales between the ridges than on the lake beach it- 

 self. Wherever it occurs, it is characteristic of moist rather than 

 wet sand. It is usually submerged for a time in spring, but the 

 ground becomes dry by the beginning of summer. This association 

 is characterized during the different seasons by well-developed aspects. 

 Throughout the aspects, plants belonging to the sedge family are the 

 dominant species; Carcx oedcri pinuila in late spring and early sum- 

 mer, Rynchospora capillacca leviseta during the serotinal season, and 

 Cyperus rivularis during the fall. Secondary species are somewhat 

 more numerous in point of numbers than in the two previous associa- 

 tions. Most of them are invaders of the different associations that 

 may follow this one. 



