164 
Ohio Biological Survey 
Here, and on the steeper slopes beneath the cliffs the succession is very 
similar. After the first tree stages are passed, mesophytism increases 
more rapidly on the shale area than above, and the undergrowth becomes 
denser than that found on steeper slopes. 
Bellevue limestone cliffs. —In every situation thus far mentioned, the 
pioneer stages are passed rapidly. This is not the case on the cliffs of 
the Bellevue limestone. No soil is found here except in crevices. The 
rock surfaces are covered with crustose lichens (Endocarpon pusilhim 
Hedw., Verrucaria nigrescens Pers., and Placodhim sideritcs (Tuck.)), 
and patches of xerophytic mosses. In the crevices are a few herbaceous 
plants, Saxifraga virginiensis, Aster Shortii, Solidago canadensis, and 
Poa compressa, with here and there a small red elm, blue ash, or hop 
hornbeam. The cliffs have still but few trees upon them, when the suc¬ 
cession on the slopes below has reached the oak forest stage. Where 
the Bellevue does not cap the bluffs, the slopes are often less steep, and 
the summits rounded instead of cliff-like. In either case the tops of the 
bluffs support a similar vegetation, which is always in a more advanced 
stage than that of the steepest slopes. Thus the cliffs may be bordered 
above by large oaks (Quercus Mulilenbergii, Q. rubra, and Q. coccinea) 
and sometimes sugar maples a short distance back from the edge. 
The succession on the Bellevue limestone cliffs is typical of resistant 
rock bluffs. It is similar to that outlined by Cowles (1901, a) as occur¬ 
ring on limestones and dolomites of the Illinois region, except that the 
conifer stage is here entirely absent. The first tree stage is its ecological 
equivalent, being followed here, as in the Illinois region, by an oak forest. 
The river bluffs nowhere show a later stage in the succession than this 
oak forest. 
The oak forest. —The oak forest varies somewhat on different expo¬ 
sures. On south slopes, oak predominates, and with it are some honey 
locust, hackberry, blue ash, and red elm. The undergrowth is made up 
largely of redbud and Crataegus with saplings of the trees named above. 
Sugar maple is occasionally an important constituent of the younger 
growth. On north slopes, sugar maple is sometimes a secondary species 
of the forest. Sweet buckeye (Aesculus octandra), basswood (Tilia 
americana), wild black cherry (Primus serotina), and walnut (Juglans 
nigra) are also mixed with oak, which is still the most abundant tree. 
Considerable difference is noted in the spring herbaceous growth of 
north and south bluffs. On the north slope, the ground cover is dense, 
and the plants are those commonly found in mesophytic forests—pale 
