40 ENVIRONMENTAL RELATIONS 



V. Thicket or Forest Margin Sub-Formations of the Savanna and Forest 

 Climates. Physiological group in the main though the "candlehead" 

 sub-formation may develop into V, 2, or VI, 7, d 



1. Wet-ground thicket sub-formations (lower strata periodically sub- 

 merged) 



a) River deposit or stream-margin thicket sub-formations. Associa- 

 tion in the development of flood-plain forest 



b) Marsh and pond-margin thicket sub-formations (first association 

 in the development of forests in marshes) 



c) Candlehead or moist forest margin sub-formation of the savanna 

 and deciduous forest climates 



2. Straussia longipennis, or high forest margin sub-formation of the 

 savanna climate (a climatic sub-formation of considerable permanency, 

 probably not usually a genetic type) 



VI. Forest Communities of the Deciduous Forest Climate 



1. Elm-ash series of communities 



a) Low prairie associations (see IV, 1) 



b) Marsh-margin thicket associations (see V, 1, b) 



c) Elm-ash associations 



2. Tamarack or floating-bog series of communities 



a) Low prairie or floating-bog association (pitcher-plant consocies) 



b) Marsh-margin thicket associations (see V, 1 , b) 



c) Tamarack-forest formations 



3. Flood-plain series of communities 



a) Terrigenous river-margin associations 



b) Stream-margin thicket associations (see V, 1, a) 



c) Elm and river-maple associations (not studied) 



4. Clay series of communities 



a) Cicindela purpurea limbalis, or bare clay association 



b) Sweet-clover association 



c) High forest margin associations (see V, 2) 



5. Rock series of communities (little studied) 



a) Bare rock consocies 



b) Thicket association (probably high forest margin, V, 2). Later 

 stages not well represented near Chicago 



6. Sand series of communities 



a) Lake-margin association 



b) Cicindela lepida, or Cottonwood association 



c) Cicindela lecontei, or the pine association 



d) Ant-lion or black-oak association 



7. Climatic forest formation of the deciduous forest climate 



a) Birch-maple association of the tamarack-forest series 



b) Panorpa, or oak-elm-basswood association of the flood-plain and 

 marsh-forest series 



