The vegetation serves as a good indicator of erosion in the 

 ravines. A ravine, or portion of a ravine, with a good mature woods that 

 contains large trees and an abundance of wildflowers has only minimal 

 erosion. The lack of this kind of vegetation indicates that either active 

 erosion is occurring or that there has been some kind of severe disturbance 

 in the past that makes revegetation difficult. 



ECOLOGY OF THE RAVINES 



Plant ecologists call the plant association found in the ravines 

 in Highland Park "maple-basswood woods" because of the prevalence of these 

 kinds of plants; the woods on the tablelands above the ravines are quite 

 different and are called "oak-hickory woods." The ravine woods have sev- 

 eral vertical layers with different kinds of plants in each layer. These 

 layers are 1) the tree canopy; 2) the understory tree layer; 3) the shrub 

 layer; and 4) the herb layer. These are discussed below (also see Fig. 1). 



Tree%:anopy . — This layer contains the tall trees that reach heights 

 up to 70 or even 100 feet and that effectively intercept most of the direct 

 sunlight. The common trees in this layer are sugar and black maples, Ameri- 

 can basswood, red oak, American ash, Norway maple (seeding-ln from trees 

 cultivated in yards and parks), white oak, cottonwood, black locust, willow, 

 and paper birch. The last four species are found primarily toward the Lake 

 Michigan end of the ravine. 



Understory tree layer . — This layer Is composed of trees that are 

 smaller than those in the canopy and that do not receive much direct sun- 

 light. The trees in this category include Ironwood, black cherry, box elder, 

 blue beech, shadbush, and hawthorn. 



Shrub layer . — The small-to-large woody shrubs that grow under the 

 trees are in this layer. These include witch hazel, several dogwoods and 



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