47 



D. The vegetation is dense and closed, dominated by trees or avevectent shrubs, 

 or by herbs in the immediate vicinity of shrubs ; the sand is stable, with 

 usually low water-content. 



The Forest Formation of the Deciduous Forest Province. 



a. The vegetation is dominated bv herbs. t-u c •; • a i^^.-^^ 



"= - The Siiiilaciua Association. 



The Physalis Association. 



b. The vegetation is dominated by shrubs, with numerous lianes, the sec- 



ondary species are of a mesophytic type. 



1. On the crests of dunes or other areas of deposition. 



The Dune Thicket Association. 



2. In blowouts The Blowout Thicket Association. 



c. The vegetation is dominated by trees. 



1 . The secondary species are generally xerophytic ; avevectent shrubs 

 or lianes are few or absent; the leaf-mold is thin or absent. 



The Black Oak Association. 



2. The secondary species are generally mesophytic; avevectent shrubs 

 and lianes are abundant ; a superficial layer of humus is de- 

 veloped. 



a. The dominant species are bur oak and white oak. 



The Bur Oak Association. 



b. The dominant vegetation is composed largely of black oak, 

 but with numerous other arborescent species. 



The Mixed Forest Association. 



The; Prairik Formation 

 the bunch-grass association 



The bimch-g'rass association formerly occupied probably more 

 than nine tenths of the iinforested portion of the sand areas. It ex- 

 tended over hill and dale, interrupted only by the blowouts and their 

 related associations, and was by far the most important association 

 of the unforested area. Monotonously uniform floristically, its eco- 

 logical structure showed an obvious differentiation into several con- 

 socies, each characterized by the preponderance of one or a few 

 species of grass, and often sharply distinct from its surroundings. 

 These are considered to be consocies instead of associations because 

 they can not be referred to any apparent difference in the environment, 

 and because they exhibit no successional relations to each other. 



The best development of the bunch-grass association was, and is, 

 in the Hanover sand area. By far the larger portion of the area was 

 originally unforested. Large fields are still in a virgin condition, 

 and hundreds of acres have been but little pastured. The area in- 

 cludes most of the consocies described and offers without doubt the 

 best conditions for ecological study. The Winnebago area includes, 

 so far as observed, but one small area of bunch-grass, not more than 

 an acre in extent, entirely surrounded by forest. It is evidently a 



