274 A NATURALIST IN THE GREAT LAKES REGION 



conspicuous. This zone is very evidently the willow zone on its 

 plant side and may be designated the cecropia larva zone on its 

 animal side. 



Farther back from the stream is the flood-plain forest proper. 

 Red and white elms, white and black and blue ash, basswood, 

 soft maple, hackberry, black cherry, black walnut, sycamore, and 

 black willow are the common trees, with white elm, white ash, and 

 soft maple dominant members of the association. In addition, 

 the Kentucky coffee tree, Gymnocladus dioica (Fig. 414), is com- 

 mon a little farther south, and when one gets away from the lake 

 in the Chicago area, the tulip tree, pawpaw, flowering dogwood, 

 and redbud are often found in the river-bottom association. 



FIG. 425. Short-tailed shrew, Blarina brevicaudata, and footprints 



Of the smaller trees the hawthorn, American crab, chokecherry, 

 and the hop tree are conspicuous. The shrubs that are character- 

 istic are buttonbush, burning bush, or wahoo, elderberry, bladder 

 nut (Fig. 416), nannyberry, prickly ash (Fig. 417), and in some 

 places the strawberry bush covers large areas of the ground. 



The river bottom association is characterized by many woody 

 vines, some of which climb up the low trees and drape them with 

 dense festoons (Fig. 415). Such are the Virginia creeper, poison 

 ivy, bittersweet, honeysuckle, moonseed (Fig. 418), and the 

 wolf grape. Several species of smilax are also common (Fig. 419). 



As in the climax forest there is present here an abundance of 

 spring herbs that bear blossoms and set their fruit before the 

 dense shade of summer is produced by the thick foliage of the 

 trees and shrubs. Skunk cabbage (Fig. 420) and marsh mari- 



