311 



Invading species from the 

 Liatris scariosa 

 Potcntilla fritticosa 

 Poa coniprcssa 

 Poa pratcnsis 

 Trifoliwn hybrid itin 

 Plant ago in a j or 

 PycnantJicinuni virginiannni 

 Taraxacum erythrospcrniuni 

 Lobelia s pi cat a 

 Satureja glabra 



prairie and prairie-like associations 

 Zizia anrea 

 Hypo. vis hirsuta 

 Sisyrinchiitm sp. ? 

 Phlox pilosa 

 Castilleja sessiliflora 

 Tradcscantia reflexa 

 Coniandra unibellata 

 Ccanothiis ovatiis 

 Bpilobium densiim 

 Bqtiisetuni laevigatuni 



Invading species from 

 HeliantJieniiini in a jus 

 Fragaria virginiana 

 Rubus occidentalis 

 Verbascnm thapsus 

 Rum ex aceto sella 

 Querciis velutina 

 Salix spp. 



Asparagus oMcinalis 

 Solidago serotina 

 Lonicera dioica 



the oak forest 



Vitis vulpina 

 Maianthenium canadense 

 Lunula cauipestris iniiltiHora 

 Helianthus occidentalis i. illinoen- 



sis 

 Ceanothus aniericanus 

 Geranium carolinianuni 

 Lactuca canadensis * 



Rosa humilis 

 Pediciilaris canadensis 



THE QUERCUS VElvUTINA ASSOCIATION 



As the climax stage of the successions on the ridges of the sand- 

 plain, this forest association exists. The association obtains its start 

 in either of the prairie or coniferous types of vegetation, quite often 

 in broken places in them. It can obtain a slight foothold upon open 

 sand, but more usually the young oaks obtain their foothold in the 

 humus of the prairie or the pines. Development then is quite certain. 

 It is rather more rapid in the prairie situations. As development pro- 

 ceeds the prairie gives way. After a time the ground begins to be 

 more open as the ground-carpet disintegrates to a greater or less ex- 

 tent. Thereupon eremacausis, at least with respect to the upper layers 

 of ground, begins again to be the usual state of affairs. This, coupled 

 with the winds of the more violent storms, causes the surface to 

 reassume a sandy appearance. The sand itself is more or less easily 

 blown, especially where the removal of any of the trees permits a 

 more open exposure. Such blowing results in the formation of what 

 are known as blowouts. While the upper layers may be sandy and 

 the secondary vegetation that of true sand ridges, in which there has 



