Bergman and Siallard: climax I'Okmattons 373 



than in the succession of uncultivated clearings. Furthermore it 

 does not exist long before Populus, Bctula and Salix seedlings enter, 

 and the succession passes rapidly from the shrub associes to the 

 Popidus-Bctiila associes. The chief shrubs found in this associes 

 are: Rubits strigosiis, Rhus glabra, Rhus rydbergii, Rosa blanda 

 and Syuiphoricarpos occidentalis. The herbs present are largely 

 relicts of the preceding associes. After Populus ircmuloides with 

 its accompanying species has invaded, the succession of trees from 

 then to the climax is essentially the same as described for unculti- 

 vated clearings on pages 359 to 361. 



(3) Populiis-Bctula Associes 



The presence of shrubs of the Corylus-Rubus associes by pro- 

 tecting the soil from exposure to the sun and wind maintains a 

 higher water-content in the soil. The shrubs also afford protection 

 to seedlings of Populus and Betida from excessive transpiration, 

 thereby permitting them to become established. 



Consocies : The consocies of this stage are Populus trermdoides, 

 P. grandidentata and Bettda papyrifera. Populus seedlings very 

 soon appear after the establishment of Corylus and Rubus in the 

 spaces not occupied by the latter. Their growth is slower than 

 Corylus, and several years are sometimes required for Populus to 

 rise above the tops of Corylus. Populus appears in practically all 

 clearings. The occurrence of Befula papyrifera is somewhat irreg- 

 ular. In some localities it is absent, while in others it is sparse. In 

 its range it is a very prominent consocies. Sometimes species of 

 Salix, especially 6". discolor, are numerous in the early stage of the 

 Populus-Betula associes. The most important shrubs are as follows : 



Amelanchier canadensis Rlius Jiirta 



Amelanchier spicafa Rosa blanda 



Cornus paniculafa Sambucus racevnosa 



Prunus serotina Xanfhoxyluni americanuni 

 Prunus virginiana 



Occasionally Celastrus scandens, Parthenocissiis occidentalis and 

 Vitis vulpina are found. 



The herbs common to this associes are : 



