Studies in Prairie and Woodland 41 



extent of an area occupied by a certain dominant or by ecolog- 

 ically equivalent dominants. Thus beginning with the slope on 

 the extreme left we find the upper portion occupied by a com- 

 munity in which Quercus macrocarpa and Quercus velutina are 

 dominant (27 large trees). Two red oaks and three red elms are 

 also present and with several saplings of red elm, an ironwood 

 and a mulberry, make up the forest. 



On the steeper slopes near the base of the ravine this forest 

 type gives way abruptly to one dominated by Tilia. Here occur 

 36 large linden trees, a few red oaks, considerable green ash, a 

 few elms and a number of the very tolerant ironwoods. It should 

 be noted that a number of trees, especially black oaks, have died. 



Proceeding up the slope we enter the Quercus macrocarpa- 

 Quercus acuminata community. The entire absence of the linden 

 here as on the corresponding opposite slope should be noted. 

 Proceeding once more down the gentle westward slope we pass 

 through a narrow belt of timber dominated by the red oak; the 

 transition being one through the black oak stage. The dead bur 

 and black oaks indicate a rather unsuitable habitat for these 

 species, probably due to the shading by the red oaks. The ap- 

 pearance of linden indicates greater mesophytism, and indeed 

 lower down the slope this species becomes dominant. 



From this transect it appears that the bur oak, yellow oak or 

 black oak communities occupy the higher ridges ; that they give 

 way on the lower slopes to red oak, which is in turn replaced near 

 the foot of the slopes and in the ravines by a community dom- 

 inated by linden. 



We will next examine a transect starting at the top of a ridge 

 91 feet above the ravine and proceeding down a long gentle north- 

 east slope; figure 16. 



The sharp top of this ridge (as is frequently the case on the 

 bluffs) is clothed with grassland. This gives way, through a 

 narrow belt of Rhus glabra and Cornus asperifolia, to a mixed 

 forest community of black, yellow and bur oak. There are a 

 number of representatives of green ash, red elm (mostly small 

 trees) and an occasional shag-bark hickory, which has migrated 

 up from lower down the slope. 



47 



