PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 



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and sedges. The following species are typicsX :—Eriophorum 

 gracile, Eriophorum callitrix, Scirpus sylvaticus, Scirpus atro- 

 virens, Scirpus polyphyllus, Carex gijnocrates, Carex tenella, 

 Carex diandra, Carex Frankii, Carex aquatilis, Typha latifolia, 

 Aster puniceiis, Spiranthes cernua, Eupatorium perfoliatum, 

 etc. Many of the rushes develop hummocks which are always 

 typical of the open swamp. It is upon these that the seedlings 

 of invading species usually first appear. 



Fig. 1. The open-swamp stage in which Typha latifolia dominates. This 

 stage is being replaced by the entrance of Alnus incana, Betula Lenta, and Acer 

 rubrum. 



The Shrub Stage 



The open stage very commonly has scattered patches of 'ow 

 shrubs which develop upon the hummocks. These invade from 

 a surrounding zone where this type is dominant in the vegetation. 

 Of these pioneers the most common are Rosa Carolina and Cornus 

 stolonifera. 



There is frequently a well defined bomidary betw^een the open 

 swamp and shrub stages. In the latter the soil has become more 



