The forest you've just entered is an OAK-HICKORY FOREST - one of several distinct plant communities that make up Severson Dells.  The two trees that characterize this forest are SHAGBARK HICKORIES (Carya ovata), like the tree just off the trail here, as well as BUR OAKS (Quercus macrocarpa), such as the large tree on the opposite side of the trail and to the right.