30 



SAND DUNE REGION OF SAGINAW BAY. 



Local and General Distribution of the Biota. 



In examining the above table account should be taken of the intensity 

 of the environic conditions. If this is done the table expresses the 

 actual conditions which are as follows: 



(1) The sand ridges support a fauna and flora composed principally 

 of those forms that are adapted to xerophytic conditions in this latitude. 



(2) The swales support the mesophytic forms of the region. 



(3) The bogs are dominated by distinctly northern forms, which are 

 also present on shaded rock cliffs. 



(4) There are very few decidedly southern forms in the biota, and 

 of those that occur here some are found on the ridges and some in the 

 lowland habitats. 



This is shown in the following analysis of the fauna and flora. 

 The more distinctly northern and southern forms in each group are 

 in bold-faced type. 



1. Forms that range widely over eastern North America both to the 

 north and south of Michigan, e. g., the pied-billed grebe, wood duck, 

 great blue heron, spotted sandpiper, kingfisher, robin, leopard. frog, 

 American toad, green frog, and a great many plants that do not need 

 to be enumerated. 



2. Southern forms that in Michigan extend considerably north of this 

 latitude, e. g., American beech, white oak, bur oak, swamp white oak, 



