SAND DUNE REGION OF SAGINAW BAY. 



29 



Saginaw Bay and the westward bend of Lake Huron exert some in- 

 fluence upon the western shores of the lake. 



Although Winchell states (pp. 282-283) that the mean annual tem- 

 perature is also slightly higher along the west coast of Michigan than on 

 corresponding latitudes west of Lake Michigan, the annual mean in 

 Huron County (as shown by Da\is) is practically the same as obtains at 

 points on corresponding parallels on the great plains so that in this re- 

 gion the lakes operate principally to check oscillations and extreme va- 

 iations. As said above, just what effect the more ecjuable temperature 

 of this coast has upon the fauna and flora cannot be determined until 

 the fauna of the remainder of Huron County and the interior of the 

 state has been worked in much greater detail. That we may expect 

 more southern forms than occur in the interior seems to be shown 

 by the biota of the west coast, where the flora at least is decidedly more 

 southern than in the interior at a given latitude.* 



It should be pointed out, also, that within the sand region on this 

 coast peculiar local conditions prevail, for the sparse vegetation and 

 consequent exposure, and the rapidity with which the sand heats up 

 acts to produce higher summer temperatures. That this is true for 

 our region is shown by a comparison of our temperature records for 

 July with the corresponding records for Hayes (in the clay country). 



'These records are taken from the July report of the Michigan Section of the chmatological 

 service of the Weather Bureau, and may be taken as representative of the conditions in the 

 clay country adjacent to the sand region. Letters represent number of days for which reccids 

 are wanting. 



^Records secured by this expedition. Thermometer placed in the woods and sheltered 

 from the sun. These records are comparable with those of Hayes. ' 



^Records secured by this expedition. Thermometer fully exposed to the sun on the 

 • north beach. 



Of the temperature conditions the most important from the stand- 

 point of the plants and animals are undoubtedly the checking of extreme 

 oscillations and the higher summer temperatm-e. Considering then 

 the physical conditions discussed we may group them on the basis 

 of their effects as follows: 



*Beal, W. J., Michigan Flora, Fifth Ann. Rept. Mich, Acad. Sci. (1903), p. 20. 



