- Transition Prairie-Forest District. 521 
priety such timber might have been described as an oak opening and the description included 
here, but as a border forest extending into the prairie and of a greater extent territorily than the 
oak groves in Illinois and elsewhere, it was thought better to consider them as a part of the 
Ozark deciduous forest Area. (See ante Chapter II. $ 3. .) 
The principal trees ofthe deciduous forests in the upper Mississippi 
basin proper are Ouercus alba, O.coccinea, O.tinctoria, O. rubra, O. macrc- 
carpa, Q. bicolor (bottom-land), ©. Muhlenbergü, Acer dasycarpum, A. rubrum 
(on sandy, black loam), Carya porcina (= Hicoria glabra), Juglans cinerea, 
37. nigra, Populus monilifera (in bottoms). The trees of the dry ridges are 
Betula papyrifera, Carya alba (= Hicoria ovata), Ouercus alba, O. macrocarpa, 
Gymnocladus canadensis (dioica), Prunus virginiana, Juniperus virginiana, Tilia 
americana and Celtis occidentalis. These are the trees between Trempealeau, 
Wisconsin and Dubuque, Iowa: Betula papyrifera, B. nigra, Juglans cinerea 
are more abundant north of this territory. The sycamore Platanus occiden- 
talis, Gleditschia triacanthos, Gymnocladus, Fuglans nigra, Qnercus Muhlen- 
bergü and Morus rubra are southern trees which have moved north along the 
great river '). 
e herbs of these moist ae in the upper Mississippi Valley are Actaea alba, A, rubra 
diantum pedatum, Aralia nudicaulis, mosa, oe a triphyllum, Asarım canadense, Dicentra 
cucullaria, Caulophyllum en Hesahn acuta (= H. acutiloba), Hydropkyiiim virginicum, 
Liparis ah ee peltatum, Pedicularis ae Viola pubescens, etc, The phyto- 
geographer is led to believe that this forest formation is an intrusion into the prairie region 
of one ei of de mesophytic forest region of Piedmont-Appalachian-Ozark type. 
The forest of this transition territory occupies three distinct types of 
physiography, viz: ridges and hill slopes, rock ledges and alluvial bottom- 
land. Each physiographic area is characterized by a distinct phytogeographic 
formation. 
Ridge and Hill Slope Forest Formation. The most conspicuous trees on 
the flat slopes are OQuercus alba,' O. rubra, O. tinctoria, Carya 
(= Hicoria ovata), Populus Bemalohdes, P. grandidentata, Tilia americana = 
casional), Os/rya, Carpinus, Fraxinus sambucifolia. — The most conspicuous 
trees of the upper slopes are Beiula papyrifera, Carpinus caroliniana, 
Ostrya virginiana, Tilia americara, Fuglans cinerea. e lower sunny 
clay slopes were in early times covered with Ouercus macrocarpa and 
O. tinctoria, the former species predominating in Wisconsin and Minnesota. 
The shaded slopes were characterized by QOucrcus alba, Q. rubra, Pirus 
tonensis, Prunus americana, P. virginiana, Corylus americana. 
Alluvial Bottom Forest Formation. The higher alluvial soils are charac- 
terized by Acer dasycarpum, Tilia americana, Ulmus americana, Populus 
monilifera, Quercus rubra, Carya amara (= Hicoria minima), Fraxinus viridis 
and occasionally Juglans nigra. The absence of Betula nigra and Onercus 
bicolor (= O. platanoides) is noteworthy. 
ı) PAmMEL, L. H.: Forest Vegetation of the upper Mississippi. Garden and Forest IV: 460, 
472, 531. 
