Ecology of the Cincinnati Region 
135 
3. Stages of the succession in depressions and on undrained flats. 
The earliest steps in the hydrarch succession in progress in the de¬ 
pressions and on the undrained flats are problematic. At first, of course, 
the succession was climatic, and the earliest stages were not such as could 
exist in these places today. If we may compare the sequence of events 
here after the retreat of the glaciers, with what we find in the north today, 
we would expect tundra and meadow vegetation, slowly encroached upon 
and restricted by the advancing forests. Today, small natural openings 
are found in the upland forests. Some are still ponds, with their typical 
marginal vegetation of sedges and buttonbush (Cephalanthus occidenta- 
lis). In others (dg. 4 ), are a few red maples and a number of sun plants 
instead of the shade plants of the rest of the forest. Still others are the 
openings about the white oak trees (dg. 12 ), with their more meadow-like 
vegetation. Are these perhaps, relicts of a former and more extensive 
formation, in time doomed to destruction by the encroachment of the 
forests? At least, they give some clue to possible earlier stages leading 
up to the present hydrophytic forests. The succession indicated here is 
also further substantiated by what is now going on in many clearings. 
Upon the broadest uplands, there are no indications of what will 
follow the swamp forest. In the next generation, at least, it will succeed 
itself. But on the smaller uplands, and wherever streams are draining 
the flats, or around the margins of depressions, is developed a mesophytic 
forest. 
4. Drained and gently rolling uplands 
It was shown in discussing the depression forest, that it is being suc¬ 
ceeded by a more mesophytic vegetation, because of the draining and 
gradual filling of the depression. Small streams are working headward 
into the broad flats, carrying off the surface water, and leaving areas 
drained but still moist. Few such upland valleys are cut through the till 
mantle; often indeed, their bottoms are but five or ten feet below the gen¬ 
eral level of the upland. This slight drainage has served to change a 
hydrophytic into a mesophytic habitat. 
Succession .—Occasionally a horizontal succession from the hydro¬ 
phytic to the mesophytic forest is seen. More rarely, the succeeding meso¬ 
phytic vegetation is foretold by the appearance of mesophytic trees in the 
undergrowth of a hydrophytic forest. The succession consists of but few 
stages. Sometimes a mixed forest intervenes between the pure hydro¬ 
phytic and the ultimate association of the succession. Often, however, 
the jump is sudden. If horizontal succession, upon a very gradually 
