130 
Ohio Biological Survey 
anywhere else. In such cases, the trunks usually stand about 8 to 10 
feet apart, and very little herbaceous vegetation is found in the dense 
shade beneath them (iig. p). Again pin oak is mixed with other trees, 
especially white oak (Quercus alba), sour gum (Nyssa sylvatica), sweet 
gum (Liquidambar Styracidua), swamp white oak (Quercus bicolor), red 
maple (Acer rubrum), shell-bark hickory (Carya ovata), and sometimes 
beech (Fagus grandifolia). Where beech occurs in the swamp forest, its 
larger roots may lie on the surface of the ground, or may be raised above 
the surface, appearing as prop roots at the base of the trunk, as illustrated 
in dg. 10. 
With the exception of swamp white oak and red maple, any tree 
which commonly occurs in the pin oak woods, may become dominant. 
Where one tree is dominant, it is usually dominant over large areas, or 
it may give way locally to a primary species. 
Thus, in the northern part of Clermont county (Milford to Blan- 
chester), pin oak is usually dominant, but often mixed with white oak, 
which locally is more abundant than the pin oak. Farther south, in 
Clermont county and in Brown county, in the vicinity of Bethel and 
Hamersville, pin oak, though still common, does not produce the pure 
stands before noted, but is mixed with sweet gum, and indeed, is often 
only one of the primary species in a sweet gum forest. White oak and 
red maple are common here also, but seldom occupy any considerable 
area exclusively. As the sweet gum forest is so similar to the pin oak 
forest in density and in moisture conditions and therefore in under¬ 
growth, it may be considered as belonging to the pin oak type, which in 
this region is the more common. 
The extensive forests of the undissected plateau can not of course 
occur in the immediate vicinity of Cincinnati. But smaller areas of the 
same type are found, wherever similar conditions are imposed. Although 
rather exceptional here, they may be considered as outliers of a prevailing 
forest type of southwestern Ohio, bearing the same relations to their 
surroundings as do the more extensive tracts. 
Much that has been said concerning depression forests, applies 
equally well to those of the flat uplands. All zonation and horizontal 
succession are absent here, except where ponds are present, introducing 
the earlier hydrophytic stages, or ravines are working headward into the 
plateau, introducing drained conditions. 
Pin oak forest. —The pin oak type of forest is well represented by 
small areas. The undergrowth is either very sparce, consisting of Car- 
