372 MIN'XESOTA I50TAXICAL STUDIES 



area may be invaded by Corylus, Riibiis, Rhus and Rosa. This oc- 

 curs always when a prairie area near woodland ceases to be burned 

 repeatedly, so that the shrubs become established. The covering 

 of grasses and herbs protects the seedlings of the shrubs which soon 

 grow up. As these increase in number by the appearance of other 

 seedlings and by sprouts from roots of older plants, the grasses are 

 killed out and the typical shrub associes takes its place. Clearing 

 alone usually results in the initiation of a secondary sviccession be- 

 ginning with this stage. When the forest is removed and the land 

 left uncultivated, the shrubs which have been suppressed because of 

 shade can now develop. Corylus soon becomes the dominant shrub. 

 Riibiis, if not present in the climax forest, is one of the earliest in- 

 vaders. 



Consocies : Corylus americana and Rubus strigosus are the us- 

 ual consocies. Rhus hirfa and R. glabra often occur as socies in this 

 associes. 



Secondary species : The most abundant secondary shrubs are 

 Rosa blanda. R. arkansana, Symphoricarpos occidcutalis, Ribes 

 gracile and Rhus rybergii. 



Herbs common to this associes will depend on many conditions, 

 as the character of the surface soil, the plants present in the sur- 

 rounding region, the time of clearing and the rapidity with which 

 Corylus makes a covering. The following may be carried over from 

 the climax association and persist under the Corylus if it is not too 

 dry from the time of clearing until shade is reestablished : 



Actaca rubra Sanicula niarilandica 



Aralia uudicaulis Suiilacina stellata 



Erigeron phUadelphicus Vvularia grandiflora 



Fragaria virginiana Vkia americana 



Lathyrus ochrolcucus Viola papiliouacca 



Lathyrus venosus Viola sororia 



Maianthonum canadcnsc IVashingtonia longistylis 



Poh'goiiatuiu coiuiiiutatum 

 Those present as a result of invasion are Aster laevis, Erigeron 



canadensis, Onagra biennis, Solidago canadensis, Ziaia aurea, and 



such grasses as Elymus canadensis, E. virginicus, Agropyron cani- 



num, A. tenermn and Agrostis alba. 



When the climax forest is removed and the land cultivated for 



a time and then abandoned, the shrub associes is slower in forming 



