358 MINNESOTA BOTANICAL STUDIES 



are usually found with A. furcatiis, but not very abundantly. Ap- 

 parently it happens that Danthunia and various herbs as described 

 above come in first, only to be replaced by Audropogun, which 

 crowds out the other plants. Other secondary species occurring 

 with A. furcatiis are the following: 



Achillea lanulosa Campanula rotundifoUa 



Agastachc anctliiodora Equisetum hiemale 



Agrostis hicmalis lirigeron ramosus 



Artemisia caudafa H clianthemum canadense 



Aster laevis Hieracimn umbellatum 



Bromus Kalmii Laciuaria scariosa 



When an area has been plowed after clearing and then aban- 

 doned, it grows up for a few years to ruderals and semi-ruderals, 

 such as Leptilon canadense, Chowpodium album, Amaranthus retro- 

 flexus, A. graecizans, Onagra biennis, Achillea lanulosa, Erigeron 

 ramosus and such grasses as Agropyron tenermn, A. caninum, Ely- 

 inus canadensis and Agrostis alba. The grasses tend to increase and 

 crowd out the weeds, but before the grasses gain control the area 

 is usually invaded by shrubs and trees, which become dominant at 

 the expense of both weeds and grasses. 



(3) Coryhis-Rubus Associes 



Following fires of less intensity and following the removal of 

 the forest by clearing, secondary succession may begin with an 

 associes of Rubus strigosus and Corylus americana. This is more 

 often true after clearing than after burning, since the former does 

 not destroy any under-shrubs which may be present. In a secondary 

 succession beginning with one of the lower stages, the shrubs in- 

 vade the herbaceous associes and soon become dominant by crowd- 

 ing out the herbs. Usually the invasion begins with the appearance 

 of Diervilla lonicera in the herbaceous associes, to be followed soon 

 by Corylus and Rubus. In the area near Ely where the surface is 

 largely of rock, Comptonia peregrina, Pteris aquilina and Diervilla 

 lonicera with Chamaenerion and Aster constitute a stage prior to 

 the appearance of the Rubus-Corylus associes. 



Consocies : The species most often found as dominants of this 

 associes, as indicated in the name, are Rubus strigosus and Corylus 

 americana. Alnus crispa and Prunus pcnnsylvanica may be found 

 as consocies, or in places may replace one or both of the usual con- 



